Laboratory Proficiency Testing: A Guide to Providers and Program Selection

Laboratory proficiency testing (PT) is a structured external assessment in which a provider distributes unknown samples to participating laboratories, the laboratories test those samples using their routine methods, and the provider evaluates each laboratory's results against established targets or peer group performance. For laboratory managers, PT serves as both a regulatory compliance requirement and a practical tool for detecting systematic errors that internal quality control may miss. This guide explains what proficiency testing measures, how to evaluate PT providers, and how to build a defensible PT selection process for a clinical or research diagnostic laboratory.

What Proficiency Testing Measures in the Clinical Laboratory

Proficiency testing evaluates the analytical phase of laboratory testing by comparing results across laboratories using identical or similar samples. The World Health Organization's Laboratory Quality Management System Handbook describes PT as a component of a broader quality management approach that supports laboratory accreditation and continuous improvement. PT does not measure the entire testing process. It focuses on whether a laboratory can produce accurate results for the specific analytes or organisms included in the survey challenge.

The distinction between proficiency testing and internal quality control matters for laboratory managers. Internal quality control uses materials with known or assigned values that the laboratory tests at regular intervals to monitor day to day precision and drift. Proficiency testing uses blinded or unknown samples that the laboratory receives from an external provider, typically two to four times per year. A laboratory can pass internal quality control while failing PT if its internal control materials share the same matrix or calibration bias as its patient testing. PT provides an independent check because the provider assigns target values through reference methods or consensus of peer laboratories.

A 1998 review in Archives of Pathology and Laboratory Medicine noted that PT data are an indicator, but not a measure, of laboratory performance. The review identified several limitations including incomplete assessment of the total testing process, PT materials being treated differently than patient samples, and matrix effects where the PT material behaves differently than fresh clinical specimens. Laboratory managers should treat PT as one quality indicator among several, not as a standalone guarantee of clinical accuracy.

The Role of Allowable Total Error in PT Program Design

Allowable total error (ATE) defines the maximum amount of error permitted for an assay when judging acceptability. According to a 2024 review in Advances in Clinical Chemistry, ATE limits are performance specifications predefined for a variety of laboratory analytes. These limits define the maximum error allowed when judging a new assay during method verification or validation, evaluating patient or instrument comparison data, or designing a quality control strategy.

The review explains that ATE resources come from several sources. They may be based on legal requirements or set by providers of proficiency testing and external quality assessment schemes. ATE can also be determined by professional expert groups or based on biological variation of an analyte. Because multiple resources exist, consensus on which ATE resource should receive preference has been difficult to reach. The review also distinguishes between allowable total error and observed total analytical error. ATE is the predefined limit, while observed total analytical error is what the laboratory actually measures during validation or PT participation.

For laboratory managers selecting a PT provider, the ATE criteria used by the provider directly affect pass or fail decisions. A provider using a stringent ATE based on biological variation will flag more laboratories than a provider using a looser legal requirement. When comparing providers, laboratory managers should request the grading criteria for each analyte or test category before enrollment. The criteria should be documented in the provider's program description or participant manual.

At a Glance: PT Provider Comparison Framework

The following table summarizes the key dimensions laboratory managers should evaluate when comparing proficiency testing providers. Use this framework during vendor assessment and before renewing annual contracts.

Core Principles of PT Provider Accreditation

ISO/IEC 17043 is the international standard that specifies general requirements for proficiency testing providers. Providers that achieve accreditation under this standard have demonstrated competence in designing PT programs, preparing and characterizing samples, analyzing participant results, and reporting outcomes. The standard also requires providers to operate a quality management system covering their PT activities.

The experience of India's first accredited EQA program in transplant immunology and immunophenotyping illustrates what provider accreditation involves. According to a 2025 report in Human Immunology, the Chimera Translational Research Fraternity conducted a gap analysis in 2019 and found strong demand for a locally accessible, cost-effective EQA program tailored to transplant immunology. The program's implementation included recruiting qualified personnel, forming a core committee to develop technical protocols, establishing a quality management system, conducting pilot surveys and internal audits, and then applying for ISO/IEC 17043 accreditation through the National Accreditation Board for Testing and Calibration Laboratories. The program obtained accreditation covering 25 analytes.

This example shows that ISO/IEC 17043 accreditation is not automatic. It requires documented procedures, pilot testing, internal audits, and successful closure of nonconformities. Laboratory managers should verify that a PT provider's accreditation certificate is current and that the accredited scope includes the specific analytes or test categories the laboratory needs.

Evaluating PT Program Design and Sample Quality

The quality of PT samples determines whether the exercise provides meaningful information. Poorly characterized or unstable samples can produce false failures that waste laboratory time and false passes that hide real problems. Laboratory managers should ask providers for sample characterization data before enrollment.

A 2026 study on proficiency samples for highly pathogenic avian influenza H5N1 detection in milk demonstrated the importance of rigorous sample development. The study used reverse transcriptase digital PCR to obtain precise genome copy measurements of virus stock and spiked samples, producing accurate quantification even at low viral loads. The researchers reported low between-sample standard deviations ranging from 0 to 0.10 real-time RT-PCR cycle threshold values for replicate samples, which fell below the theoretical threshold indicative of heterogeneity. Parallel analysis of milk-based and buffer-based samples showed no indication of a matrix effect, and samples remained stable for at least 28 days when stored at minus 80 degrees Celsius.

For laboratory managers, these findings translate into specific questions for PT providers. Ask whether the provider has performed homogeneity testing on the sample lot. Ask whether stability studies have been conducted under the shipping conditions used for distribution. Ask whether the provider has characterized the sample matrix and whether that matrix matches or approximates the clinical specimens the laboratory routinely tests.

A 2026 study on external quality assessment for yaws elimination in low and middle income countries used plasmid-based proficiency test items containing gene target sequences for Treponema pallidum and Haemophilus ducreyi. The proficiency testing panel included seven swabs loaded with different concentrations of plasmids in different combinations, plus human cells to simulate sample background. The plasmid-based items proved stable in dry conditions with no significant loss of copy number. Participating laboratories achieved quantitative PCR concordance of 95.0 to 100.0 percent with the provider, while loop-mediated isothermal amplification results showed lower concordance, particularly for low target levels combined with high background levels.

This study illustrates two practical points. First, synthetic or plasmid-based PT materials can be stable and suitable for molecular testing programs, especially in settings where live organisms are difficult to distribute. Second, PT results can vary by method type. A laboratory using a less sensitive method may fail PT challenges that a more sensitive method passes. When selecting a provider, laboratory managers should confirm that the program's peer groups account for method differences.

Practical Workflow for PT Program Selection

Laboratory managers need a repeatable process for evaluating and selecting PT providers. The following workflow can be adapted to any laboratory setting.

Step 1: Define the PT Requirement

List every test or analyte the laboratory reports clinically. For each test, determine whether PT is required by an accrediting body, a regulatory agency, or a professional standard. The College of American Pathologists proficiency testing surveys, for example, are used by many laboratories to meet accreditation requirements. The World Health Organization Laboratory Quality Management System Handbook describes PT as part of the quality system essential for accreditation.

Step 2: Identify Candidate Providers

Search for providers that offer PT for the laboratory's test menu. Consider both large international providers and regional or specialty providers. The 2025 report on India's transplant immunology EQA program noted that a significant gap existed in accredited EQA providers specializing in that field, which prompted the development of a new program. Specialty providers may exist for niche testing areas where large providers do not offer coverage.

Step 3: Request Documentation

Ask each candidate provider for the following documents before enrollment:

• Current ISO/IEC 17043 accreditation certificate and scope
• Program description including grading criteria and target value assignment methods
• Sample preparation and characterization procedures
• Homogeneity and stability data for the relevant sample types
• Participant manual including reporting deadlines and result submission procedures
• Fee schedule including any additional charges for late enrollment or extra surveys

Step 4: Compare Grading Criteria

For each analyte the laboratory needs covered, compare how each provider assigns target values and defines acceptable performance. A 2024 review of external quality assessment for semen analysis in Clinical Chemistry and Laboratory Medicine found that different EQA organizers choose different ways to calculate assigned values and acceptance limits. The review reported large coefficients of variation across participating laboratories for concentration, motility, morphology, and viability. This variability means that the same laboratory could pass one provider's program and fail another's for the same analyte.

Step 5: Assess Sample Matrix Compatibility

Review whether the provider's PT samples match the laboratory's routine specimen types. For molecular testing, determine whether the samples are nucleic acid extracts, dried specimens, or whole organisms. For microbiology, determine whether the samples are viable organisms, inactivated organisms, or nucleic acid targets. A laboratory that routinely tests formalin-fixed paraffin-embedded tissue should seek a provider that distributes similar material for molecular PT challenges.

Step 6: Check Peer Group Composition

Ask the provider for the number of participants in each peer group relevant to the laboratory's methods. Small peer groups can produce unstable consensus targets. A 2018 study of multi-laboratory proficiency testing for clinical cancer genomic profiling by next-generation sequencing involved 15 European molecular diagnostic laboratories using three different platforms and multiple target enrichment systems. The study demonstrated high inter-laboratory agreement after implementing a multi-level filtering strategy. This study shows that PT can work across platforms, but it also shows that peer group composition and data analysis methods affect outcomes.

Step 7: Review Corrective Action Support

Determine what happens after a failed PT event. Does the provider offer root cause analysis guidance? Does the provider provide educational feedback explaining the expected results? Does the provider allow the laboratory to submit a corrective action report? A 2005 study on detection and correction of systematic laboratory problems by analysis of clustered proficiency testing failures addressed how laboratories can use patterns of PT failures to identify systematic issues. Providers that support this type of analysis add more value than providers that only report scores.

Step 8: Pilot the Program

If feasible, enroll in one survey cycle before committing to a multi-year contract. Use the pilot cycle to evaluate sample quality, shipping reliability, result submission processes, and report clarity. Document any issues and discuss them with the provider before renewal.

Records and Measurements for PT Oversight

Laboratory managers should maintain structured records for PT participation. These records support accreditation audits, regulatory inspections, and internal quality reviews.

Required Records

Maintain the following for each PT event:

• Provider name and program identifier
• Survey or challenge identifier
• Date samples received and date results submitted
• Analyst or technologist who performed the testing
• Method, instrument, and reagent lot numbers used
• Results submitted for each sample
• Provider evaluation report including scores and target values
• Any corrective action documentation

Performance Tracking

Track PT performance over time using the following measures:

• Percentage of acceptable results per survey event
• Number of unacceptable results per analyte or test category
• Trends in bias or imprecision across consecutive surveys
• Time from PT failure to corrective action completion
• Recurrence of failures for the same analyte or method

A 2024 study of drinking water microbiology proficiency testing in Canada evaluated 150 rural and metropolitan testing sites between 2016 and 2022. The study used multivariable logistic regression to examine the impact of testing method and laboratory accreditation status on proficiency scores. This type of longitudinal analysis can reveal whether laboratory characteristics such as accreditation status or method choice are associated with PT performance. Laboratory managers can apply similar analysis to their own PT records to identify patterns.

Common Failure Patterns in Proficiency Testing

Understanding why laboratories fail PT helps managers design effective corrective actions. The following patterns appear across multiple studies and program types.

Matrix Effects

PT materials may behave differently than fresh patient samples. The 1998 review in Archives of Pathology and Laboratory Medicine identified matrix effects as a limitation of current PT practices. A laboratory may perform well with patient samples but fail PT because the PT material produces different results with the laboratory's method. When this pattern appears, the laboratory should document the matrix issue and communicate with the provider. Some providers can supply alternative sample formats or clarify whether the matrix effect is a known limitation.

Method Sensitivity Differences

PT challenges may include samples at concentrations near the detection limit of certain methods. A 2026 study of African swine fever virus detection in Chinese provincial veterinary laboratories found that all 37 participating laboratories achieved 100 percent consistency in qualitative results. However, in the quantitative assessment, 89.19 percent of participants qualified in 2020 and 94.6 percent qualified in 2021. Among the four participants with unsatisfactory results in 2020, one failed to detect two diluted weak positive samples while the other three failed to detect strong positive samples. This pattern shows that failures can occur at both high and low concentrations, and that weak positive samples challenge method sensitivity.

Transcription and Data Entry Errors

PT failures sometimes result from errors in recording or submitting results instead of from analytical problems. Laboratories should implement a second-person review of PT results before submission. The review should confirm that the correct units were used, that results were transcribed accurately from the instrument, and that the correct sample identifiers were matched to the correct results.

Calibration Drift

A laboratory may pass internal quality control while failing PT because its calibration has drifted relative to the reference method or peer group. The 2024 review in Advances in Clinical Chemistry noted that ATE limits define the maximum error allowed when evaluating patient or instrument comparison data. When PT failures cluster around a specific analyte or instrument, the laboratory should perform a calibration verification and compare results against a reference method if available.

Clustered Failures

A 2005 study on detection and correction of systematic laboratory problems by analysis of clustered proficiency testing failures addressed how laboratories can identify systematic issues from patterns of PT failures. When multiple analytes fail in the same survey event, the cause may be a common preanalytical step, a shared reagent, or an instrument malfunction. When the same analyte fails across multiple survey events, the cause may be a method-specific bias or an ATE criterion that the method cannot meet.

Limitations of Proficiency Testing

Laboratory managers should understand what PT cannot do. The 1998 review in Archives of Pathology and Laboratory Medicine emphasized that PT data are an indicator, not a measure, of laboratory performance. PT does not assess the preanalytical phase including specimen collection, transport, and processing. PT does not assess the postanalytical phase including result reporting, interpretation, and clinical communication.

PT samples are often treated differently than patient samples. Laboratory staff may give PT samples special attention, run them in duplicate, or verify results before submission. This practice, sometimes called the PT effect, can produce artificially good results that do not reflect routine performance. The 1998 review suggested that occasional use of blind PT, where samples are submitted without staff knowledge, could address this limitation.

PT programs may not cover all tests the laboratory performs. For rare analytes or emerging methods, no PT program may exist. In these cases, laboratories should consider alternative assessment strategies such as inter-laboratory comparison with a partner laboratory, split sample testing with a reference laboratory, or participation in research-based PT programs. A 2019 pilot study of inter-laboratory proficiency testing for tumor next-generation sequencing in Ontario involved one reference laboratory providing samples to four participating laboratories. This type of collaborative arrangement can fill gaps when commercial PT is unavailable.

Safety and Regulatory Context for PT Participation

PT participation intersects with laboratory safety and regulatory requirements in several ways.

Biosafety Considerations

PT samples may contain infectious agents or hazardous materials. The World Health Organization Laboratory Biosafety Manual provides guidance on safe handling of biological materials in the laboratory. Laboratory managers should ensure that PT samples are handled according to the same biosafety level as patient specimens with similar risk characteristics. Providers should ship PT samples in compliance with applicable transport regulations for infectious substances or diagnostic specimens.

For molecular PT programs using synthetic materials such as plasmids, the biosafety risk may be lower than for programs using live organisms. The 2026 yaws EQA study used plasmid-based proficiency test items, which are stable and do not require propagation of live Treponema pallidum. Laboratory managers should review the provider's safety data sheets and shipping documentation before accepting PT shipments.

Regulatory Requirements

Many accreditation programs require PT participation as a condition of accreditation. The World Health Organization Laboratory Quality Management System Handbook describes PT as part of the quality system essential for laboratory accreditation. Laboratory managers should verify the specific PT requirements of their accrediting body, including the number of surveys per year, the analytes that must be covered, and the acceptable performance threshold.

Some regulatory programs require laboratories to take corrective action after PT failures. The corrective action should include root cause analysis, implementation of corrective measures, and verification that the measures resolved the problem. The laboratory should document all steps and retain records for inspection.

Professional Escalation Criteria

Laboratory managers should escalate PT issues to senior leadership or external authorities under specific conditions:

• Repeated PT failures for the same analyte despite corrective action
• PT failures that suggest a patient safety risk
• PT failures involving multiple analytes or multiple instruments
• Inability to identify the root cause of a PT failure
• Disagreement with the provider's grading that cannot be resolved through the provider's appeal process

A 2022 study in Archives of Pathology and Laboratory Medicine on incidental and secondary germline findings during tumor testing noted that robust recommendations must take into account test design and validation, reimbursement, cost, infrastructure, impact on reflex testing, and maintenance of proficiency. This finding applies to PT oversight as well. Laboratory managers should consider whether PT failures indicate a need for method changes, additional validation, or consultation with the test manufacturer.

PT for Molecular and Genomic Testing

Molecular and genomic testing presents specific PT challenges that laboratory managers should understand when selecting providers.

Next-Generation Sequencing PT

Next-generation sequencing (NGS) enables parallel analysis of multiple genomic targets. A 2018 study in Pathology, Research and Practice described a multi-laboratory PT program in which formalin-fixed paraffin-embedded specimens from eight lung and eight colon cancers were analyzed by 15 European molecular diagnostic laboratories on three different platforms. The study demonstrated accuracy, scalability, and robustness of NGS through PT, serving as a benchmark for detecting clinically actionable molecular alterations.

A 2019 pilot study of tumor NGS PT in Ontario found excellent technical concordance across participating institutions. All sites achieved 100 percent concordance in the technical identification of 98 exonic variants across 10 cases. However, variability between laboratories in the choice of variants considered clinically reportable was significant. Of 38 variants reported as clinically relevant by at least one site, only 3 were concordantly reported by all participating centers.

For laboratory managers, these findings have two implications. First, technical accuracy for NGS can be assessed through PT, and high concordance is achievable. Second, PT programs for NGS should assess also variant identification but also reporting practices. When selecting an NGS PT provider, laboratory managers should ask whether the program evaluates clinical reporting or only technical variant calling.

Whole Genome Sequencing PT

Whole genome sequencing (WGS) has been incorporated into routine reference laboratory practice for pathogen surveillance. A 2024 study in Pathology described a PT program that evaluated the capacity and capability of one New Zealand and 14 Australian public health laboratories to perform WGS of SARS-CoV-2. Participants were assessed on genome coverage, Pango lineage, and sequence quality. The study found that more participants would have failed the 2021 assessment when the more stringent 2022 metrics were applied, highlighting the importance of choosing appropriate performance metrics.

Laboratory managers should review the assessment metrics used by WGS PT providers. Metrics that focus only on consensus sequence accuracy may miss problems with coverage or quality. The 2024 study showed that refining assessment metrics can change pass or fail outcomes significantly.

Fragile X and Repeat Expansion Testing

Molecular genetic testing of the FMR1 gene is commonly performed in clinical laboratories. A 2021 technical standard from the American College of Medical Genetics and Genomics noted that the ACMG Laboratory Quality Assurance Committee reviews the outcome of national proficiency testing in the genetics area and may focus on specific diseases or methodologies in response to those results. Fragile X syndrome was selected as a focus topic because it is one of the most frequently ordered genetic tests and has many alternative methods with different strengths and weaknesses.

For laboratory managers, this example shows that PT programs for genetic tests must account for methodological diversity. Southern blot analysis and polymerase chain reaction amplification of FMR1, including triplet repeat-primed and methylation-specific PCR, have different performance characteristics. When selecting a PT provider for genetic testing, laboratory managers should confirm that the provider's peer groups account for method differences.

Glioma Biomarker Testing

A 2022 study in Archives of Pathology and Laboratory Medicine used College of American Pathologists proficiency testing survey results from 96 laboratories performing molecular testing for diffuse gliomas. The study found that more than 98 percent of participating laboratories performed testing for glioma biomarkers recognized as diagnostic for specific subtypes, including IDH. More than 60 percent of laboratories used molecular markers to differentiate between astrocytic and oligodendroglial lineage tumors. Almost all laboratories tested for MGMT promoter methylation.

The study highlighted gaps between laboratory practices in 2020 and recommendations in the 2021 World Health Organization Classification of Central Nervous System Tumors. For laboratory managers, this finding shows that PT survey data can reveal the state of laboratory practice and identify areas where testing is not universal. When selecting PT programs, laboratory managers should consider whether the program reflects current classification standards and whether it includes emerging biomarkers.

PT for Microbiology and Infectious Disease Testing

Microbiology PT programs present unique considerations related to sample viability, biosafety, and method diversity.

Bacterial Detection and Quantification

A 2024 study of drinking water microbiology PT in Canada evaluated Escherichia coli detection by environmental testing laboratories. The program provided PT challenges twice per year, with each challenge consisting of four samples containing unknown concentrations of E. coli and Enterobacter species. The study examined the impact of testing method and laboratory accreditation status on proficiency scores.

For laboratory managers, this study demonstrates that PT programs can assess both qualitative and quantitative performance in microbiology. When selecting a microbiology PT provider, laboratory managers should confirm that the program includes samples at clinically relevant concentrations and that the provider's grading criteria account for method-specific performance characteristics.

Viral Detection

A 2026 study on proficiency samples for highly pathogenic avian influenza H5N1 detection in milk demonstrated the development of fit-for-purpose samples for interlaboratory evaluation of RT-PCR detection. The study used reverse transcriptase digital PCR to quantify genome copies and validated sample homogeneity and stability. The defined assay sensitivity, expressed as the level of detection 50 percent, was determined for the reference assay.

Laboratory managers should ask microbiology PT providers whether their samples have been characterized using reference methods and whether homogeneity and stability data are available. Samples that are not well characterized can produce misleading PT results.

Telemicrobiology and Digital PT

A 2016 review in Archives of Pathology and Laboratory Medicine examined telemicrobiology, which enables remote interpretation of digital images of microbiology specimens. The review noted that telemicrobiology has been successfully implemented for several applications including routine primary diagnosis, expert teleconsultation, and proficiency testing. Static image capture techniques have been the most widely used modality.

For laboratory managers, digital PT formats may offer advantages for morphology-based assessments such as parasite identification, fungal morphology, or Gram stain interpretation. Digital PT eliminates shipping and stability concerns for these sample types. However, laboratory managers should verify that the digital images are of sufficient quality for the intended assessment.

PT for Specialized Testing Areas

Several specialized testing areas have unique PT considerations that laboratory managers should evaluate when selecting providers.

Hemostasis Testing

A 2019 article in Clinical Chemistry and Laboratory Medicine addressed harmonization of external quality assessment and proficiency testing in hemostasis. The article's title indicates that harmonization efforts are needed in this area. Laboratory managers should be aware that hemostasis PT programs may vary in their target value assignment methods and grading criteria. When selecting a hemostasis PT provider, laboratory managers should compare how the provider handles reagents, instruments, and method differences.

Drug of Abuse Testing

A 2020 article in Archives of Pathology and Laboratory Medicine addressed interpretation and utility of drug of abuse screening immunoassays, with insights from laboratory drug testing proficiency surveys. The article's title indicates that PT surveys can provide insights into how laboratories interpret drug screening results. Laboratory managers should ensure that their PT provider covers the specific drug classes and cutoff concentrations relevant to their testing menu.

Semen Analysis

A 2024 review in Clinical Chemistry and Laboratory Medicine examined how external quality assessment and proficiency testing of semen analysis has developed over 34 years. The review found inconsistent implementation of EQA across different countries and no global consensus. Policies vary from country to country, with some countries mandating participation and others permitting voluntary involvement. The review reported large coefficients of variation for concentration, motility, morphology, and viability across participating laboratories.

For laboratory managers, this review highlights the importance of understanding the PT provider's assigned value calculation and acceptance limits. The same laboratory could receive different PT outcomes from different providers for the same semen analysis parameters.

Transplant Immunology and Immunophenotyping

A 2025 report in Human Immunology described the establishment of India's first accredited EQA program in transplant immunology and immunophenotyping. The program obtained ISO/IEC 17043 accreditation covering 25 analytes. The report noted that external quality assessment is mandated by international standards such as ISO/IEC 15189 to ensure laboratory competence and comparability across institutions.

For laboratory managers in specialized fields, this example shows that accredited PT programs may not exist for all testing areas. When no accredited provider exists, laboratory managers should consider whether a non-accredited provider with documented quality systems can meet their needs, or whether inter-laboratory comparison with partner laboratories is a viable alternative.

Building a PT Program Evaluation Checklist

Laboratory managers can use the following checklist when evaluating PT providers. The checklist consolidates the considerations discussed throughout this guide.

Provider Qualifications

• Does the provider hold current ISO/IEC 17043 accreditation?
• Does the accreditation scope include the analytes or test categories the laboratory needs?
• Has the provider published its quality management system documentation?
• Does the provider participate in any oversight or peer review programs?

Program Design

• How are target values assigned for each analyte?
• What ATE sources or performance specifications are used for grading?
• Are the grading criteria published and available before enrollment?
• How many survey events are offered per year?
• What is the deadline for result submission?

Sample Quality

• Has the provider performed homogeneity testing on the sample lot?
• Have stability studies been conducted under shipping conditions?
• What is the sample matrix and does it match the laboratory's routine specimens?
• Are sample characterization data available on request?

Peer Groups

• How many participants are in each peer group?
• How are peer groups defined for method, instrument, and reagent differences?
• What happens when a peer group has fewer than a minimum number of participants?

Reporting and Support

• What information is included in the PT report?
• Does the report include target values, acceptable ranges, and peer group statistics?
• Does the provider offer educational feedback or root cause analysis guidance?
• Is there an appeal process for disputed grades?
• What corrective action support does the provider offer after failures?

Logistics

• What are the shipping methods and delivery times?
• Are samples shipped with appropriate temperature control?
• What is the fee structure and are there additional charges?
• What is the enrollment deadline and is late enrollment permitted?

Common Failure Patterns and Corrective Actions

Laboratory managers should develop a structured approach to PT failure investigation. The following table summarizes common failure patterns, likely causes, and recommended corrective actions.

A 2026 study of African swine fever virus detection in Chinese provincial veterinary laboratories found that among four participants with unsatisfactory quantitative results in 2020, one failed to detect two diluted weak positive samples while the other three failed to detect strong positive samples. This pattern shows that both weak and strong positive samples can produce failures, and the corrective actions differ. Weak positive failures suggest sensitivity issues, while strong positive failures suggest hook effects, dilution errors, or calibration problems.

Professional Escalation Criteria

Laboratory managers should escalate PT issues beyond the laboratory when specific conditions are met. The following criteria define when to involve senior leadership, the provider, or external authorities.

Escalate to Senior Leadership When

• PT failures recur for the same analyte after two corrective action cycles
• PT failures suggest a risk to patient safety
• PT failures involve multiple instruments or multiple sites
• The laboratory cannot identify the root cause of a PT failure
• PT failures require capital investment for new equipment or methods

Escalate to the PT Provider When

• The laboratory disagrees with the grading or target value assignment
• The PT samples appear damaged, degraded, or improperly shipped
• The provider's report lacks sufficient information for root cause analysis
• The provider's peer group composition is inadequate for the laboratory's method

Escalate to External Authorities When

• PT failures indicate a systemic quality problem that could affect patient results
• The laboratory is unable to resolve PT failures despite documented corrective action
• Regulatory or accreditation requirements mandate reporting of PT failures
• PT failures suggest a public health concern

The 2022 study on incidental and secondary germline findings during tumor testing noted that maintenance of proficiency is one of several factors that must be considered in robust testing recommendations. Laboratory managers should treat PT as a continuous quality activity instead of a periodic compliance exercise. PT failures should trigger investigation, corrective action, and verification, beyond documentation.

Frequently Asked Questions

What is the difference between proficiency testing and external quality assessment?

Proficiency testing and external quality assessment are often used interchangeably, but they have distinct meanings. Proficiency testing is a specific type of external quality assessment in which a provider distributes samples to multiple laboratories and evaluates their results against established targets or peer group performance. External quality assessment is a broader term that includes proficiency testing as well as other activities such as on-site assessment, split sample testing with a reference laboratory, and educational surveys. The World Health Organization Laboratory Quality Management System Handbook describes external quality assessment as a component of laboratory quality management. Laboratory managers should verify whether their accrediting body requires proficiency testing specifically or accepts other forms of external quality assessment.

How often should a laboratory participate in proficiency testing?

Participation frequency depends on regulatory requirements, accreditation standards, and the laboratory's test menu. Most accreditation programs require participation at least two times per year for each regulated analyte or test category. Some programs require quarterly participation. The drinking water microbiology PT program described in a 2024 study provided challenges twice per year. Laboratory managers should verify the specific requirements of their accrediting body and enroll in programs that meet or exceed those requirements. For tests without mandated PT, laboratories should consider voluntary participation at least annually to monitor performance.

What should a laboratory do after failing a proficiency testing event?

The laboratory should immediately investigate the failure, document the investigation, and implement corrective action. The investigation should include review of the PT samples, the testing method, the instrument, the reagents, and the personnel involved. The laboratory should determine whether the failure was due to an analytical problem, a sample handling issue, a transcription error, or a method limitation. Corrective action should address the root cause and include verification that the action resolved the problem. The laboratory should retain all records for accreditation audits and regulatory inspections. If the laboratory disagrees with the provider's grading, it should use the provider's appeal process.

Can a laboratory use proficiency testing results to evaluate new methods?

Proficiency testing results can inform method evaluation, but they should not be the sole basis for method selection. The 2024 review in Advances in Clinical Chemistry noted that ATE limits define the maximum error allowed when judging acceptability of a new assay during method verification or validation. PT results can show whether a method meets the ATE criteria used by the provider. However, PT samples may not represent the full range of patient samples the method will encounter. Laboratory managers should combine PT results with method validation data, comparison studies, and clinical correlation when evaluating new methods.

What is a matrix effect in proficiency testing?

A matrix effect occurs when the PT sample material behaves differently than fresh patient samples in the laboratory's testing method. The 1998 review in Archives of Pathology and Laboratory Medicine identified matrix effects as a limitation of current PT practices. PT samples may be lyophilized, frozen, or otherwise processed to improve stability and homogeneity. These processes can alter the sample matrix and affect certain methods. When a laboratory suspects a matrix effect, it should document the issue, compare results across multiple survey events, and communicate with the provider. Some providers can supply alternative sample formats or provide information about known matrix limitations.

How does proficiency testing differ for qualitative and quantitative tests?

Qualitative tests report the presence or absence of a target, while quantitative tests report a measured value. PT grading differs accordingly. For qualitative tests, the provider evaluates whether the laboratory's result matches the expected result. For quantitative tests, the provider evaluates how close the laboratory's value is to the target value, using criteria such as ATE or z-scores. A 2026 study of African swine fever virus detection used qualitative evaluation based on consistency with reference results and a z-score evaluation system for quantitative assessment. A 2024 article in Accreditation and Quality Assurance described an S-score for binary qualitative proficiency testing schemes that is interpretable as the z-score. Laboratory managers should understand which grading approach applies to each of their tests.

What is the role of peer groups in proficiency testing?

Peer groups are groups of laboratories that use similar methods, instruments, or reagents. The provider calculates peer group statistics, including the consensus mean and standard deviation, for each group. Target values may be based on the peer group consensus or on a reference method. Peer group composition affects the stability and validity of the target value. Small peer groups can produce unstable consensus targets. A 2018 study of NGS proficiency testing involved 15 laboratories using three different platforms, and the study demonstrated high inter-laboratory agreement after implementing a multi-level filtering strategy. Laboratory managers should ask providers about peer group size and composition before enrollment.

How can a laboratory verify that a proficiency testing provider is accredited?

Laboratory managers should request a copy of the provider's ISO/IEC 17043 accreditation certificate and verify that the certificate is current. The certificate should list the accredited scope, including the specific PT programs or analytes covered. Laboratory managers can also check with the accreditation body that issued the certificate to confirm its validity. The 2025 report on India's transplant immunology EQA program described the process of obtaining ISO/IEC 17043 accreditation through the National Accreditation Board for Testing and Calibration Laboratories. Laboratory managers should verify that the provider's accreditation covers the specific programs they intend to enroll in, beyond the provider's overall operations.

Related Diagnostic Guides

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References and Further Reading

• Laboratory Quality Management System Handbook. World Health Organization.
• Laboratory Biosafety Manual. World Health Organization.
• Assay Guidance Manual. National Center for Advancing Translational Sciences.
• Bioanalytical Method Validation Guidance. U.S. Food and Drug Administration.
• NCBI Literature Resources. National Center for Biotechnology Information.
• Defining allowable total error limits in the clinical laboratory.. Advances in clinical chemistry, 2024.
• Laboratory testing for fragile X, 2021 revision: a technical standard of the American College of Medical Genetics and Genomics (ACMG).. Genetics in medicine : official journal of the American College of Medical Genetics, 2021.
• Laboratory and Clinical Implications of Incidental and Secondary Germline Findings During Tumor Testing.. Archives of pathology & laboratory medicine, 2022.
• Multi-laboratory proficiency testing of clinical cancer genomic profiling by next-generation sequencing.. Pathology, research and practice, 2018.
• Proficiency testing in laboratory medicine: uses and limitations.. Archives of pathology & laboratory medicine, 1998.
• Review of Telemicrobiology.. Archives of pathology & laboratory medicine, 2016.
• Clinical Laboratory Testing Practices in Diffuse Gliomas Prior to Publication of 2021 World Health Organization Classification of Central Nervous System Tumors.. Archives of pathology & laboratory medicine, 2022.
• Inter-laboratory proficiency testing scheme for tumour next-generation sequencing in Ontario: a pilot study.. Current oncology (Toronto, Ont.), 2019.
• Establishing India's first accredited EQA program in transplant immunology and Immunophenotyping: The CHIMERA® EQA experience.. 2025.
• Evaluation of capabilities of Chinese provincial veterinary laboratories in detection of African swine fever virus: a proficiency testing program.. 2026.
• Development of Fit-for-Purpose, High Quality Proficiency Samples for Interlaboratory Evaluation of RT-PCR Detection of HPAI H5N1 in Milk.. 2026.
• External quality assessment for yaws elimination in low- and middle-income countries using plasmid-based proficiency test items.. 2026.
• S-score: a new score for binary qualitative proficiency testing schemes interpretable as the z-score. Accreditation and Quality Assurance, 2024.
• Continued improvement in the development of the SARS-CoV-2 whole genome sequencing proficiency testing program.. Pathology (Sydney), 2024.
• Improving drinking water quality through proficiency testing-the impact of testing method and accreditation status on Escherichia coli detection by Canadian environmental testing laboratories. Frontiers in Molecular Biosciences, 2024.
• How has the external quality assessment/proficiency testing of semen analysis been developed in the past 34 years: a review. Clinical Chemistry and Laboratory Medicine, 2024.
• EXPLORING ANXIETY, WILLINGNESS TO COMMUNICATE AND LANGUAGE PROFICIENCY AMONG KAZAKHSTANI EFL LEARNERS. Bulletin of Toraighyrov University Pedagogics Series, 2025.
• Doctors should choose communication strategies based on the patient's attitude toward disease and healthcare workers: a study in Jiangsu, China. Frontiers in Health Services, 2025.
• Supplementing provider counseling with an educational video prior to scheduled induction of labor. BMC Pregnancy and Childbirth, 2024.
• Navigating a ‘Perfect Storm’ on the Path to Prevention of Type 2 Diabetes Mellitus After Gestational Diabetes: Lessons from Patient and Provider Narratives. Maternal and Child Health Journal, 2019.
• New criteria for proficiency assessment of clinical laboratories by interlaboratory comparisons. Journal of Physics Conference Series, 2018.
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• Interpretation and utility of drug of abuse screening immunoassays: Insights from laboratory drug testing proficiency surveys. Archives of Pathology and Laboratory Medicine, 2020.

This article is educational and does not replace validated laboratory procedures, institutional biosafety review, manufacturer instructions, or professional interpretation.