Selectivity and Specificity in Method Validation

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-08-27

Quick Answer

• Selectivity describes a method's ability to measure a target analyte distinctly from other components, while specificity is the stronger claim of measuring only the target without any interference.
• For validation protocols, use interference testing and matrix effect experiments to demonstrate selectivity, and reserve specificity claims for methods with proven absolute response to one analyte.
• The distinction matters because regulatory language in ICH and FDA guidance uses both terms, and mislabeling a method as specific when it is only selective can undermine validation credibility.

At a Glance

Defining Selectivity and Specificity in Analytical Validation

The terms selectivity and specificity describe how well an analytical method distinguishes the target analyte from everything else in the sample. In practice, laboratories often use these words interchangeably, but validation protocols require a precise distinction. Selectivity means the method can measure the target analyte without significant bias from other components. Specificity means the method responds to the target analyte alone, with no measurable response from any other substance under the validated conditions.

The International Council for Harmonisation guidance Q2(R1) on validation of analytical procedures uses selectivity as the preferred term for most methods. This choice reflects the practical reality that most analytical methods respond to a family of related compounds or to the target plus some background signal. A method that is selective can still produce a small response from a structurally similar compound, but that response must be small enough to not affect the accuracy of the target measurement.

The United States Food and Drug Administration guidance for bioanalytical method validation uses specificity in a stricter sense. A specific method produces a response that comes entirely from the target analyte. This standard is difficult to meet for complex biological samples, so most validated methods are selective instead of specific. When a validation protocol claims specificity, the evidence must show that no other substance in the sample matrix contributes to the measured signal.

Why the Distinction Matters for Validation Protocols

The choice between selectivity and specificity changes the experimental design and the strength of the claim you can make. If you validate a method as selective, you must demonstrate that known interferents do not bias the measurement beyond an acceptable threshold. If you validate a method as specific, you must demonstrate that the response is attributable to the target analyte alone, often using orthogonal techniques such as mass spectrometry or a second chromatographic method.

For diagnostic assays, the distinction has direct consequences for clinical interpretation. A selective assay may produce a small response from a structurally similar compound, which could matter if that compound is present at high concentration in a patient sample. A specific assay does not have this limitation. The validation report must state which claim the method supports, because the clinical laboratory uses that claim to decide how to interpret borderline results.

The National Institute of Standards and Technology laboratory programs emphasize measurement science and calibration quality. In that context, the distinction between selectivity and specificity affects the uncertainty budget of a measurement. A method that is only selective has a known source of potential bias from interferents, and that bias must be quantified and documented. A method that is specific has no such bias, but the evidence for specificity must be rigorous.

Regulatory Definitions and Guidance

ICH Validation Guidance

The ICH guidance on validation of analytical procedures describes the parameters that should be evaluated when validating a method. The guidance uses selectivity as the term for the ability to measure the analyte in the presence of other components. This includes impurities, degradation products, and matrix components. The guidance does not require that a method be specific in the absolute sense, because most methods cannot meet that standard.

For a chromatographic method, selectivity is demonstrated by showing that the target analyte peak is resolved from other peaks in the chromatogram. The resolution factor between the target peak and the nearest interfering peak must be sufficient for accurate integration. For a spectroscopic method, selectivity is demonstrated by showing that the target analyte spectrum is not distorted by the presence of other compounds.

The ICH approach is practical because it acknowledges that methods operate in complex matrices. A method that is selective for the target analyte in the presence of known interferents is acceptable for most applications. The validation protocol should list the interferents that were tested and the concentration range over which the method remained selective.

FDA Bioanalytical Method Validation Language

The FDA guidance for bioanalytical method validation uses specificity to describe a method that measures the target analyte without interference from other substances. This is a stronger claim than selectivity. The guidance requires that the method be able to distinguish the analyte from endogenous matrix components, metabolites, and co-administered drugs.

For a bioanalytical method, specificity is demonstrated by analyzing blank matrix samples from multiple sources. The blank samples should show no response at the retention time or mass transition of the target analyte. If a blank sample shows a response, the method is not specific for that matrix source, and the validation must document the limitation.

The FDA guidance also requires that the method be able to distinguish the analyte from its metabolites. This is particularly important for drugs that are metabolized to compounds with similar structure. The method must be able to separate the parent drug from the metabolite, or the validation must show that the metabolite does not contribute to the measured response.

How the Two Guidance Documents Relate

The ICH and FDA guidance documents use different terms for similar concepts. ICH uses selectivity as the general term for the ability to measure the analyte in the presence of other components. FDA uses specificity for the stricter claim that the method responds only to the target analyte. In practice, a method that meets the FDA specificity requirement also meets the ICH selectivity requirement, but the reverse is not necessarily true.

For a validation protocol, the choice of term depends on the intended use of the method. A method used for drug release testing may only need to be selective, because the formulation is known and the interferents are limited. A method used for a bioanalytical study in a complex matrix may need to be specific, because the matrix is variable and the interferents are not fully known.

The National Library of Medicine provides access to molecular biology and laboratory methods references that describe the practical details of these validation approaches. These references can help a laboratory design the experiments needed to demonstrate selectivity or specificity for a particular method.

Experimental Design for Demonstrating Selectivity

Interference Testing

Interference testing is the primary experimental design for demonstrating selectivity. The method is tested with the target analyte in the presence of other compounds that might be in the sample. The other compounds include matrix components, degradation products, and structurally similar compounds.

The design of an interference test depends on the method type. For a chromatographic method, the test involves injecting a solution containing the target analyte and a potential interferent. The chromatogram is examined to see if the interferent produces a peak that overlaps with the target peak. For a spectroscopic method, the test involves measuring the spectrum of the target analyte in the presence of the interferent and comparing it to the spectrum of the target alone.

The concentration of the interferent should be relevant to the sample type. For a method that measures a drug in plasma, the interferent concentration should be the maximum concentration expected in a patient sample. For a method that measures a contaminant in water, the interferent concentration should be the maximum concentration expected in the water source.

Matrix Effect Evaluation

Matrix effects are a common cause of poor selectivity. The matrix is everything in the sample except the target analyte. The matrix can contain salts, proteins, lipids, and other compounds that affect the method response.

For a chromatographic method with mass spectrometric detection, matrix effects are often evaluated by comparing the response of the analyte in a neat solution to the response of the analyte in a matrix extract. If the matrix suppresses or enhances the response, the method is not selective for the matrix.

The evaluation of matrix effects should include multiple matrix sources. A method that is selective for one plasma source may not be selective for another plasma source. The validation should include matrix from at least six different sources to demonstrate that the method is selective across the expected range of matrix variability.

Blank Sample Testing

Blank sample testing is a direct way to demonstrate selectivity. A blank sample is a sample that does not contain the target analyte. The blank sample is processed through the method and the response is measured. If the blank sample produces a response at the target analyte signal, the method is not selective.

The blank sample should be representative of the sample matrix. For a method that measures a drug in plasma, the blank sample should be plasma from a person who has not taken the drug. For a method that measures a contaminant in water, the blank sample should be water from the source that does not contain the contaminant.

The number of blank samples tested should be sufficient to demonstrate that the method is selective. The FDA guidance recommends testing blank samples from multiple sources. The response of the blank samples should be below the limit of detection of the method.

Experimental Validation for Demonstrating Specificity

Orthogonal Method Confirmation

Specificity is a stronger claim than selectivity, so the experimental design must be more rigorous. One approach is to confirm the identity of the measured response using an orthogonal method. An orthogonal method is a method that uses a different physical principle to measure the same analyte.

For example, a liquid chromatography method with ultraviolet detection can be confirmed using liquid chromatography with mass spectrometric detection. If the ultraviolet method shows a peak at the retention time of the target analyte, the mass spectrometric method can confirm that the peak has the mass of the target analyte. This confirmation demonstrates that the response is attributable to the target analyte and not to a co-eluting compound.

The orthogonal method should be validated to the same standard as the primary method. The orthogonal method should be able to distinguish the target analyte from the same interferents that were tested in the primary method. The confirmation should be performed on samples that contain the target analyte and on samples that contain potential interferents.

Mass Spectral Confirmation

Mass spectral confirmation is a powerful tool for demonstrating specificity. A mass spectrometer can measure the mass-to-charge ratio of the target analyte and its fragments. The mass spectrum of the target analyte is a fingerprint that can be used to distinguish it from other compounds.

For a method that uses mass spectrometric detection, the specificity is demonstrated by monitoring the mass transitions that are specific to the target analyte. The method should monitor at least two mass transitions, one for the target analyte and one for a stable isotope-labeled internal standard. The ratio of the two transitions should be consistent with the expected ratio for the target analyte.

The mass spectral confirmation should be performed in the presence of the matrix. The matrix can contain compounds that produce the same mass-to-charge ratio as the target analyte. The method must be able to distinguish the target analyte from these matrix components.

The Limits of Specificity Claims

Specificity is a strong claim, and it is not always possible to demonstrate. For a method that measures a compound in a complex matrix, there may be compounds that produce a response that cannot be distinguished from the target analyte. In this case, the method cannot be called specific, and the validation must state the limitation.

The limitation should be described in the validation report. The report should list the compounds that were tested and the compounds that could not be distinguished from the target analyte. The report should also describe the conditions under which the method is selective, even if it is not specific.

The practical consequence of a specificity limitation is that the method may produce a false positive result. If a sample contains a compound that produces the same response as the target analyte, the method will report the target analyte as present. The validation report should state this limitation so that the user of the method can interpret the results correctly.

Practical Workflow for Validation

Step 1: Define the Method and Its Intended Use

The first step in validation is to define the method and its intended use. The method should be described in detail, including the sample preparation, the separation, and the detection. The intended use should be described in terms of the sample matrix, the concentration range, and the required accuracy.

The definition of the intended use determines the validation experiments. A method that is used for a clinical diagnostic will have different validation requirements than a method that is used for a research study. The validation should be designed to demonstrate that the method is fit for its intended use.

Step 2: Identify Potential Interferents

The second step is to identify the potential interferents. The interferents are the compounds that could be present in the sample and could affect the method response. The interferents should be identified based on the sample matrix, the sample preparation, and the detection method.

For a method that measures a drug in plasma, the potential interferents include the metabolites of the drug, the other drugs that the patient may be taking, and the endogenous compounds in the plasma. For a method that measures a contaminant in water, the potential interferents include the other contaminants in the water and the matrix components.

The list of potential interferents should be as complete as possible. The validation should test the method against the interferents that are most likely to be present and that are most likely to interfere.

Step 3: Design the Interference Experiments

The third step is to design the interference experiments. The experiments should be designed to test the method against the potential interferents. The experiments should include the target analyte at a known concentration and the interferent at a concentration that is relevant to the intended use.

The experiments should be designed to detect both false positive and false negative results. A false positive result is a response that is attributed to the target analyte but is actually caused by an interferent. A false negative result is a response that is not attributed to the target analyte but should be.

The experiments should be repeated to demonstrate that the results are reproducible. The number of replicates should be sufficient to demonstrate that the method is selective or specific.

Step 4: Run the Experiments and Record the Results

The fourth step is to run the experiments and record the results. The results should be recorded in a validation report. The report should include the method description, the interferents tested, the results of the experiments, and the conclusions.

The results should be recorded in a way that is clear and reproducible. The report should include the raw data, the calculations, and the statistical analysis. The report should be reviewed by a second person to ensure that the results are correct.

Step 5: Interpret the Results and Make a Claim

The fifth step is to interpret the results and make a claim. The claim should be based on the results of the experiments. If the method can measure the target analyte in the presence of the interferents, the method is selective. If the method can measure the target analyte in the presence of the interferents and the response is attributable to the target analyte alone, the method is specific.

The claim should be stated in the validation report. The claim should be supported by the data. The claim should be consistent with the intended use of the method.

Records and Measurements

What to Record in a Validation Report

The validation report should record the method description, the experimental design, the results, and the conclusion. The method description should include the sample preparation, the separation conditions, the detection conditions, and the data analysis. The experimental design should include the interferents tested, the concentrations used, and the number of replicates.

The results should be recorded in a table or a graph. The table should include the response of the target analyte in the presence of each interferent. The graph should show the response of the target analyte as a function of the interferent concentration.

The conclusion should state whether the method is selective or specific. The conclusion should be supported by the data. The conclusion should be consistent with the intended use of the method.

How to Measure Selectivity

The selectivity of a method can be measured by the resolution between the target analyte peak and the nearest interfering peak. The resolution is a measure of the separation between the two peaks. A resolution of 1.5 or greater is generally considered to be acceptable for a chromatographic method.

The selectivity can also be measured by the recovery of the target analyte in the presence of the interferent. The recovery is the ratio of the measured concentration to the true concentration. A recovery of 100 percent indicates that the interferent does not affect the measurement.

The selectivity should be measured at multiple concentrations of the target analyte. The selectivity at the low concentration is important because the method is more likely to be affected by the interferent at the low concentration.

How to Document the Matrix Effect

The matrix effect should be documented in the validation report. The matrix effect is the ratio of the response of the analyte in the matrix to the response of the analyte in a neat solution. A matrix effect of 100 percent indicates that the matrix does not affect the response.

The matrix effect should be measured for each matrix source. The matrix effect should be measured at multiple concentrations of the analyte. The matrix effect should be reported as a percentage with the standard deviation.

The matrix effect should be evaluated in the context of the method. A matrix effect of 90 percent may be acceptable for a method that has a low limit of detection. A matrix effect of 90 percent may not be acceptable for a method that has a high limit of detection.

Common Failure Patterns

Interfering Peaks That Overlap

A common failure pattern is the presence of an interfering peak that overlaps with the target peak. The interfering peak can be caused by a matrix component, a degradation product, or a structurally similar compound. The overlapping peak can cause the method to overestimate the concentration of the target analyte.

The failure is detected by the interference testing. The method is tested with the target analyte and the potential interferent. The chromatogram shows two peaks that overlap. The resolution between the two peaks is less than the acceptable threshold.

The failure is corrected by changing the separation conditions. The mobile phase composition can be changed to improve the resolution. The column type can be changed to improve the separation. The detection conditions can be changed to reduce the response of the interfering peak.

Matrix Suppression or Enhancement

The matrix suppression or enhancement is a common failure pattern for mass spectrometric methods. The matrix components can suppress or enhance the ionization of the target analyte. The suppression or enhancement can cause the method to underestimate or overestimate the concentration of the target analyte.

The matrix effect is detected by comparing the response of the analyte in the matrix to the response of the analyte in a neat solution. The matrix effect is measured as a percentage. A matrix effect of less than 100 percent indicates suppression. A matrix effect of greater than 100 percent indicates enhancement.

The matrix effect is corrected by using an internal standard. The internal standard is a compound that is similar to the target analyte but is not present in the sample. The internal standard is added to the sample before the extraction. The response of the target analyte is normalized to the response of the internal standard.

Carryover from a Previous Sample

The carryover is a common failure pattern for methods that use a shared injection system. The carryover is the response of the target analyte in a blank sample that is injected after a sample that contains a high concentration of the target analyte. The carryover can cause the method to report a false positive result for the blank sample.

The carryover is detected by injecting a blank sample after a sample that contains a high concentration of the target analyte. The blank sample shows a response at the target analyte signal. The carryover is measured as the ratio of the response of the blank sample to the response of the high-concentration sample.

The carryover is corrected by changing the injection system. The injection needle should be washed between injections. The injection system should be flushed with a solvent that can remove the target analyte.

Quality Controls and Documentation

The Role of Quality Controls in Validation

Quality controls are samples that contain a known concentration of the target analyte. The quality controls are used to monitor the performance of the method during the validation. The quality controls are analyzed at the beginning, the middle, and the end of the validation.

The quality controls should be prepared in the same matrix as the samples. The quality controls should be prepared at multiple concentrations. The quality controls should be prepared from a separate stock solution than the calibration standards.

The quality controls are used to calculate the accuracy and the precision of the method. The accuracy is the difference between the measured concentration and the true concentration. The precision is the variability of the measured concentration.

Documentation Standards for Validation

The validation report should be documented in a way that is clear and reproducible. The report should include the method description, the experimental design, the results, and the conclusion. The report should be reviewed by a second person to ensure the accuracy.

The documentation should be consistent with the standards of the laboratory. The laboratory should have a standard operating procedure for the validation. The standard operating procedure should describe the steps of the validation and the documentation requirements.

The documentation should be stored in a secure location. The documentation should be available for review by the regulatory authorities. The documentation should be retained for the period required by the laboratory.

The MIQE Guidelines for qPCR Methods

The MIQE guidelines provide a framework for the reporting of qPCR methods. The guidelines are intended to improve the transparency of qPCR experiments. The guidelines require that the method report the key parameters of the experiment, including the sample preparation, the amplification conditions, and the data analysis.

The MIQE guidelines are relevant to the validation of qPCR methods. The guidelines require that the method report the specificity of the amplification. The specificity is demonstrated by the melting curve analysis or the gel electrophoresis. The guidelines require that the method report the efficiency of the amplification.

The MIQE guidelines are a useful reference for the validation of qPCR methods. The guidelines provide a checklist of the parameters that should be reported. The guidelines help to ensure that the method is reproducible and that the results are interpretable.

Biosafety and Regulatory Context

Biosafety Principles for Laboratory Methods

The laboratory methods used for the validation of selectivity and specificity may involve the use of biological samples. The biological samples may contain infectious agents. The laboratory should follow the biosafety principles to protect the laboratory workers and the environment.

The biosafety principles are described in the Biosafety in Microbiological and Biomedical Laboratories. The principles include the risk assessment, the containment, and the institutional oversight. The risk assessment should identify the hazards of the biological samples. The containment should be appropriate for the risk of the biological samples.

The laboratory should follow the biosafety principles for the validation of the method. The laboratory should use the appropriate personal protective equipment. The laboratory should use the appropriate containment for the biological samples.

Institutional Oversight for Recombinant Nucleic Acid Work

The validation of a method that involves recombinant or synthetic nucleic acid molecules should follow the NIH Guidelines for Research Involving Recombinant or Synthetic Nucleic Acid Molecules. The guidelines describe the oversight for the research. The oversight includes the institutional biosafety committee and the institutional review board.

The guidelines describe the containment for the recombinant or synthetic nucleic acid molecules. The containment should be appropriate for the risk of the molecules. The containment should be described in the protocol.

The laboratory should follow the NIH guidelines for the validation of the method. The laboratory should obtain the approval of the institutional biosafety committee before the work. The laboratory should follow the containment requirements of the guidelines.

Professional Escalation Criteria

The validation of a method should be performed by a qualified person. The qualified person should have the training and the experience to perform the validation. The qualified person should be able to interpret the results and make the claim.

The validation should be reviewed by a second person. The second person should be a person who is qualified to review the validation. The second person should be able to identify the errors in the validation.

The validation should be escalated to the laboratory director if the results are not clear. The laboratory director should be able to interpret the results and make the decision. The laboratory director should be able to determine the next steps for the validation.

Decision Framework for Claiming Selectivity Versus Specificity

The choice between claiming selectivity and claiming specificity is not a matter of preference. It is a decision that determines the experimental burden, the regulatory defensibility, and the clinical or manufacturing consequences of the method. A structured decision framework helps validation teams avoid overclaiming specificity without adequate evidence and underclaiming selectivity when the data already support a stronger statement.

Step 1: Classify the Method by Detection Principle

The detection principle sets the ceiling for what claim is even possible. Methods that rely on a single physical measurement, such as ultraviolet absorbance, fluorescence, or a single mass transition, cannot support a specificity claim without orthogonal confirmation. The measurement itself cannot distinguish the target analyte from a co-eluting compound that shares the same spectral or mass characteristics.

Methods that use two or more independent measurement principles, such as tandem mass spectrometry with two product ion transitions and an ion ratio check, can approach specificity. But the claim still requires evidence that the ion ratio is stable across matrix sources and that no tested interferent produces the same ratio. The National Institute of Standards and Technology laboratory programs describe measurement science principles that apply here, including the need to quantify uncertainty from every step of the measurement process.

Step 2: Assess the Matrix Variability

The matrix variability determines how many sources must be tested and whether a specificity claim is defensible. A method that measures a drug in a well-characterized formulation buffer has a limited set of potential interferents. A method that measures a biomarker in human plasma drawn from a diverse patient population has an unknown set of endogenous compounds that could interfere.

For a method with a variable matrix, the decision framework requires a specificity claim to be supported by testing across at least six independent matrix sources. The blank samples from each source must show no response at the target signal. If any source produces a response, the method is selective for the tested sources but not specific across the expected population. The validation report must state this limitation.

Step 3: Assess the Consequences of a False Positive

The consequence of a false positive result determines the acceptable risk. A method used for a screening assay where a positive result triggers a confirmatory test can tolerate a lower level of selectivity. A method used for a release test where a positive result leads to product rejection needs a higher level of confidence.

The decision framework should include a risk assessment that answers three questions. First, what is the cost of a false positive result? Second, what is the cost of a false negative result? Third, which interferents are most likely to be present at a concentration that would cause a false result? The answers to these questions determine whether the method needs to be selective or specific.

Step 4: Match the Claim to the Evidence

The claim must match the evidence. If the evidence shows that the method can measure the target analyte in the presence of tested interferents, the claim is selectivity. If the evidence shows that the method produces a response only from the target analyte across all tested matrix sources and interferents, the claim is specificity.

The decision framework should be documented in the validation protocol before the experiments begin. The protocol should state which claim the method is expected to support and what evidence would be required. If the evidence does not support the expected claim, the protocol should describe the conditions under which the claim would be downgraded from specificity to selectivity.

Step 5: Document the Decision and the Rationale

The decision should be recorded in the validation report with the rationale. The report should state the claim, the evidence that supports the claim, and the limitations of the claim. The report should also state the conditions under which the claim would not apply, such as a matrix source that was not tested or an interferent that was not evaluated.

The documentation should be reviewed by a second qualified person. The reviewer should confirm that the evidence supports the claim and that the limitations are stated clearly. The reviewer should also confirm that the claim is consistent with the intended use of the method.

Record System for Selectivity and Specificity Evidence

A record system for selectivity and specificity evidence should be designed before the validation experiments begin. The system should capture the interferents tested, the matrix sources used, the concentrations evaluated, and the results of each experiment. The system should also capture the conditions of the method, including the sample preparation, the separation conditions, and the detection conditions.

The Interferent Log

The interferent log is a table that lists each interferent tested, the concentration tested, the matrix used, and the result. The result should be recorded as the response of the interferent relative to the response of the target analyte at the limit of quantitation. The log should also record the source of the interferent, such as a reference standard, a degradation product, or a matrix component.

The interferent log should be updated as new interferents are identified. The log should be reviewed at the end of the validation to confirm that all potential interferents have been tested. The log should be included in the validation report.

The Matrix Source Table

The matrix source table should record each matrix source tested, the source identifier, the date of collection, and the response of the blank sample. The response of the blank sample should be recorded as the signal at the target analyte retention time or mass transition. The table should also record the matrix effect for each source, calculated as the ratio of the response of the analyte in the matrix to the response of the analyte in a neat solution.

The matrix source table should include at least six sources for a method intended for a variable matrix. The table should be reviewed to confirm that the method is selective across the tested sources. If any source shows a response above the limit of detection, the method is not specific for that source.

The Claim Decision Record

The claim decision record should state the claim, the evidence, and the rationale. The record should be completed after the experiments are finished and the results are reviewed. The record should be signed by the analyst and the reviewer.

The claim decision record should include the conditions under which the claim would not hold. The conditions should include the matrix sources that were not tested, the interferents that were not evaluated, and the concentration range over which the claim is valid. The record should be stored with the validation report.

Troubleshooting When the Claim Is Not Supported

When the evidence does not support the expected claim, the method should be examined to identify the source of the interference. The troubleshooting should follow a systematic process that isolates the source of the problem.

Isolate the Interference Source

The first step is to determine whether the interference comes from the matrix, the sample preparation, or the detection system. The method should be run with a neat solution of the target analyte to confirm that the detection system is working correctly. The method should then be run with a blank matrix sample to determine whether the matrix produces a response. The method should then be run with the target analyte in the matrix to determine whether the matrix affects the response.

The comparison of the three runs identifies the source of the interference. If the blank matrix produces a response, the interference comes from the matrix. If the target analyte in the matrix produces a different response than the target analyte in the neat solution, the interference comes from the matrix effect.

Adjust the Separation or Detection Conditions

If the interference comes from the matrix, the separation conditions should be adjusted. The mobile phase composition can be changed to improve the resolution between the target peak and the interfering peak. The column type can be changed to provide a different selectivity. The detection conditions can be changed to reduce the response of the interfering compound.

If the interference comes from the detection system, the mass transitions should be reviewed. The method should use a mass transition that is specific to the target analyte. The method should monitor at least two mass transitions and the ion ratio should be consistent with the expected ratio.

Re-test and Document the Change

The method should be re-tested after the change. The re-test should include the interferents that were tested in the original validation. The re-test should also include the matrix sources that were tested in the original validation. The results should be recorded in the validation report.

The change should be documented in the validation report. The report should state the original method, the change, and the reason for the change. The report should also state the results of the re-test and the new claim.

Professional Escalation Criteria

The decision to claim selectivity or specificity should be escalated to the laboratory director when the evidence is not clear. The escalation should occur when the method cannot be made selective for the intended matrix, when the method cannot be made specific for the intended use, or when the claim is not supported by the evidence.

The laboratory director should review the evidence and the decision. The director should determine whether the method is fit for the intended use. The director should also determine whether the method needs to be changed or whether the intended use needs to be changed.

The escalation should be documented in the validation report. The report should state the reason for the escalation, the decision of the director, and the next steps. The report should be retained with the validation documentation.

Frequently Asked Questions

What is the difference between selectivity and specificity in method validation?

Selectivity is the ability of a method to measure the target analyte in the presence of other components. Specificity is the ability of a method to measure the target analyte alone. Selectivity is a weaker claim than specificity. A method that is selective can be affected by the other components, but the effect is small enough to be acceptable. A method that is specific is not affected by the other components.

Why does the FDA use the term specificity while ICH uses selectivity?

The FDA guidance for bioanalytical method validation uses specificity to describe a method that measures the target analyte without interference. The ICH guidance for drug validation uses selectivity to describe a method that measures the target analyte in the presence of other components. The difference in the terms reflects the different requirements of the two guidance documents.

How do I demonstrate selectivity for a chromatographic method?

The selectivity of a chromatographic method is demonstrated by the interference testing. The method is tested with the target analyte and the potential interferents. The chromatogram is examined to see if the target peak is resolved from the interfering peaks. The resolution should be greater than the acceptable threshold.

How do I demonstrate specificity for a mass spectrometric method?

The specificity of a mass spectrometric method is demonstrated by the mass spectral confirmation. The method is tested with the target analyte and the potential interferents. The mass spectrum of the target analyte is compared to the mass spectrum of the interferents. The method should be able to distinguish the target analyte from the interferents.

What is the matrix effect and why does it matter?

The matrix effect is the effect of the matrix on the response of the target analyte. The matrix can suppress or enhance the response. The matrix effect matters because it can cause the method to underestimate or overestimate the concentration of the target analyte. The matrix effect should be evaluated in the validation.

What should I do if my method is not specific?

If the method is not specific, the validation should state the limitation. The validation should describe the compounds that could not be distinguished from the target analyte. The validation should describe the conditions under which the method is specific. The user of the method should be aware of the limitation.

What is the role of quality controls in validation?

The quality controls are used to monitor the accuracy of the method. The quality controls are samples that contain a known concentration of the target analyte. The quality controls are analyzed at the beginning, the middle, and the end of the validation. The quality controls are used to calculate the accuracy and the precision of the method.

What are the biosafety considerations for validation?

The validation of a method may involve the use of biological samples. The biological samples may contain infectious agents. The laboratory should follow the biosafety principles to protect the safety of the laboratory and the environment. The laboratory should follow the guidelines for the containment of the biological samples.

Using the Evidence

Related Diagnostic Guides

• Method Validation in Clinical Laboratories: A Practical Protocol
• Biosafety Cabinet Principles: How They Work and How to Use Them Effectively
• Biosafety Level 4 Laboratories: Design, Operational Protocols, and Diagnostic Applications
• Biosafety Protocols for Diagnostic Specimen Transport: Ensuring Safety and Compliance
• Cell Viability Assays: Choosing the Right Method for Your Experiment

References and Further Reading

• Molecular Biology and Laboratory Methods. National Library of Medicine.
• Biosafety in Microbiological and Biomedical Laboratories. CDC and NIH.
• NIH Guidelines for Recombinant or Synthetic Nucleic Acid Molecules. National Institutes of Health.
• Addgene Protocols. Addgene.
• MIQE Guidelines. Clinical Chemistry.
• NIST Laboratory Programs. National Institute of Standards and Technology.
• Laboratory Biosafety Manual. World Health Organization.
• NCBI Literature Resources. National Center for Biotechnology Information.
• Nutritional risk screening (NRS 2002): a new method based on an analysis of controlled clinical trials.. Clinical nutrition (Edinburgh, Scotland), 2003.
• Prediction of Bacteremia and Bacterial Meningitis Among Febrile Infants Aged 28 Days or Younger.. JAMA, 2026.
• 2020 list of human papillomavirus assays suitable for primary cervical cancer screening.. Clinical microbiology and infection : the official publication of the European Society of Clinical Microbiology and Infectious Diseases, 2021.

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