# Quality Control in Veterinary Laboratory Testing: A Practical Guide


## Key Takeaways

- Internal Quality Control (IQC) involves running control materials with patient samples at least once daily for tests used daily, or each day of use for infrequent tests, to detect analytical drift and imprecision.
- External Quality Assessment (EQA), or proficiency testing, evaluates a laboratory's performance against peer laboratories using unknown samples, and participation in veterinary-specific programs with quarterly review of reports is recommended.
- Levey-Jennings charts are essential for visualizing control values over time, enabling the detection of trends and shifts, and should be interpreted using multi-rule criteria like Westgard rules to identify when a run must be rejected.
- Method validation, including precision and accuracy studies, must be performed before introducing any new test or instrument into clinical service, followed by ongoing calibration verification after calibration, major maintenance, or reagent lot changes.
- Reference intervals must be verified for the specific instrument, reagent system, and patient population in use, and re-verified whenever any of these components change to ensure accurate interpretation of patient results.
- Documentation of all QC results, control lot numbers, reagent lot numbers, and corrective actions is critical for identifying recurring failure patterns and ensuring the reliability of reported diagnostic data.

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Veterinary practice laboratories generate results that directly inform diagnosis, treatment, and monitoring decisions. Those results are only as trustworthy as the quality systems surrounding them. This guide provides a practical framework for implementing quality control (QC) in veterinary practice laboratories, covering internal quality control, external quality assessment, and the interpretive logic that connects QC data to clinical decisions. It is written for practicing veterinarians who supervise in-house testing, whether in a small animal clinic, an ambulatory equine practice, or a production animal setting.

The distinction between quality assurance, quality control, and quality assessment is frequently blurred in everyday use, but each term names a different layer of the same system. Quality assurance is the overarching program of policies and procedures that ensure testing is fit for purpose. Quality control refers to the operational techniques and activities used to verify that test performance remains within acceptable limits. External quality assessment, sometimes called proficiency testing, evaluates a laboratory's performance against peer laboratories using unknown samples. All three layers are needed, and none substitutes for another. The [American Society for Veterinary Clinical Pathology quality assurance guidelines](https://www.asvcp.org/page/QALS_Guidelines) provide a structured framework for building these layers into a veterinary laboratory.

## At a Glance

| Parameter | What to Know | Action |
|---|---|---|
| Internal quality control (IQC) | Runs control materials with patient samples to detect drift and imprecision | Run at least one control level per test per day of use |
| External quality assessment (EQA) | Unknown samples from a provider, compared against peer laboratories | Enroll in a veterinary-specific program, review reports within 30 days |
| Control material | Commercial or in-house material with an assigned target value | Store per manufacturer instructions, record lot numbers |
| Levey-Jennings charts | Plot control values over time to visualize drift and shifts | Apply Westgard rules when control limits are exceeded |
| Calibration verification | Confirms the analytical measurement range remains valid | Perform after calibration, major maintenance, or reagent lot change |
| Reference intervals | Must be verified for the instrument and population in use | Re-verify whenever the instrument, reagent, or population changes |
| Method validation | Establishes precision, accuracy, and reportable range before clinical use | Document before introducing any new test or instrument |

## The Scientific Basis of Quality Control

Laboratory measurements are subject to two classes of error. Random error, or imprecision, reflects the inherent variability of the analytical system and appears as scatter around a mean value. Systematic error, or bias, is a consistent displacement of results from the true value. QC materials are designed to detect both. A control material is a stable sample with a known concentration of the analyte of interest, run through the entire testing process alongside patient samples. When control values fall outside expected limits, the analytical system has likely drifted or shifted, and patient results generated during that period are suspect.

The statistical logic of QC rests on the assumption that control values follow a predictable distribution around their target mean. Under ideal conditions, 95% of control measurements fall within two standard deviations of the mean, and 99.7% fall within three standard deviations. A single control value beyond two standard deviations may occur by chance in 1 of 20 runs, which is why modern QC practice uses multi-rule interpretation instead of a single threshold. The Westgard rules, named for their originator, provide a structured set of decision criteria that balance the detection of true error against the rejection of acceptable runs. These rules are widely implemented in veterinary laboratory software and are described in the [ASVCP quality assurance and laboratory standards guidelines](https://www.asvcp.org/page/QALS_Guidelines).

## Internal Quality Control

Internal quality control is the daily verification that a test system is performing within its established limits. The core components are control materials, defined acceptance criteria, and a documented response to out-of-range results.

### Control Materials and Their Limitations

Commercial control materials are manufactured to be stable across reagent lots and instrument platforms. They are available in multiple concentration levels, typically low, normal, and high, which allows detection of errors that affect only part of the analytical range. Some veterinary practices use pooled patient serum as a low-cost alternative, but this approach carries risks. In-house pools lack assigned target values, may vary between batches, and can be affected by the same matrix interferences that affect patient samples. Commercial controls are preferred for most analytes, particularly when the laboratory is subject to accreditation or regulatory oversight.

### Frequency and Placement of Controls

The frequency of control runs should reflect the risk of undetected error. For a chemistry analyzer used daily, one control level per test per day is the minimum standard. For tests used infrequently, controls should be run on each day of use. For point-of-care instruments, controls should be run at the frequency specified by the manufacturer, and at least once per day when the instrument is in continuous use. Controls should be positioned in the run to detect errors that may develop during the analytical session, which means placing them at the beginning, and for longer runs, at intervals throughout.

### Interpreting Control Results

Control results should be plotted on a Levey-Jennings chart, a simple graph of control value against time, with lines marking the mean and one, two, and three standard deviations. This visual record reveals trends that a single out-of-range value cannot. A gradual drift across several consecutive runs suggests reagent deterioration or instrument wear. A sudden shift suggests a change in reagent lot, calibration, or environmental conditions. The Westgard rules provide specific decision criteria: for example, a single control value beyond three standard deviations, or two consecutive values beyond two standard deviations on the same side of the mean, both indicate the run should be rejected. When a run is rejected, patient results from that run should not be reported until the cause is identified and corrected.

## External Quality Assessment

External quality assessment (EQA) provides an independent check on laboratory performance. An EQA provider distributes unknown samples to participating laboratories, which test them and return results. The provider then compares each laboratory's results against a peer group mean or a reference method value. This process detects bias that internal QC cannot, because internal QC materials are tested by the same instrument, reagents, and operator that produce patient results. A systematic error present in the entire system will not be visible in internal control data, but will appear when results are compared against other laboratories.

Veterinary-specific EQA programs are available through several professional organizations and commercial providers. Participation should be scheduled at least quarterly for each major instrument platform. When EQA results indicate a problem, the laboratory should review the previous internal QC data, check for reagent or calibration changes, and investigate potential preanalytical factors such as sample handling or storage. The [MSD Veterinary Manual](https://www.msdvetmanual.com/) provides background on the clinical significance of common laboratory analytes, which helps interpret whether an EQA discrepancy is likely to affect clinical decisions.

## Method Validation and Verification

Before a new test or instrument enters clinical service, its performance must be established. Full method validation, which includes precision, accuracy, linearity, and interference studies, is the responsibility of the instrument manufacturer or reference laboratory. The practice laboratory performs method verification, a more limited process that confirms the instrument performs as claimed in the specific setting where it will be used. Verification should include a precision study using control materials, a comparison of patient samples against a reference method if available, and confirmation that the reportable range covers the clinically relevant interval. The [ASVCP guidelines](https://www.asvcp.org/page/QALS_Guidelines) specify the minimum verification studies required for different test categories.

## Reference Intervals and Their Maintenance

A reference interval is only valid for the instrument, reagent system, and population on which it was established. When any of these change, the interval must be re-verified. This is a common source of error in veterinary practice, where an instrument may be replaced with a different model that uses the same reagents, or a reagent lot change may shift results by a small but clinically meaningful amount. Reference interval verification can be performed with a small number of samples from healthy animals, typically 20 per species, with the interval accepted if a defined proportion of results fall within the existing range. The [MSD Veterinary Manual](https://www.msdvetmanual.com/) offers species-specific guidance on expected values for common analytes, which serves as a useful cross-check when verifying intervals.

## Building the QC Schedule

A practical QC schedule balances statistical rigor against the realities of a working practice laboratory. The schedule must specify which assays receive daily control testing, which receive weekly or monthly testing, and which require lot-to-lot verification only. The decision criteria depend on test volume, clinical consequence of error, and the stability of the analytical system.

High-volume hematology and biochemistry analyzers used for sick-patient assessment warrant daily controls. Low-volume tests performed on stable platforms, such as urine chemistry strips, may require weekly controls with lot-level verification. Coagulation analyzers, given their sensitivity to reagent and sample handling, justify controls with every run or at least daily when the instrument is in use. The [American Society for Veterinary Clinical Pathology quality assurance guidelines](https://www.asvcp.org/page/QALS_Guidelines) provide a structured framework for assigning control frequency based on assay risk and clinical use.

### Template: Core QC Schedule

| Assay Category | Control Frequency | Minimum Materials | Action on Failure |
|---|---|---|---|
| In-clinic hematology (CBC) | Daily, plus after reagent lot change | Commercial 2-level control (normal, abnormal) | Repeat control, if still out, run patient samples on backup method or refer |
| In-clinic biochemistry | Daily, plus after cuvette or reagent change | Commercial 2-level control covering reportable range | Document, troubleshoot per algorithm, hold patient results |
| Coagulation (PT, aPTT) | Each run or daily | 2-level control, verify reagent lot with parallel testing | Recalibrate or change reagent lot, verify with fresh normal sample |
| Urine dipstick | Weekly and with each new bottle | Manufacturer control strip or in-house known sample | Discard bottle, open new lot, re-test |
| Electrolyte/ blood gas | Daily or per manufacturer | 2-level aqueous control | Flush system, recalibrate, repeat |
| Fecal flotation | Monthly or with new flotation solution batch | Known positive sample or commercial control | Remake solution, verify specific gravity |
| Cytology stains | With each new stain batch | Known smear or commercial control slide | Adjust staining time or replace stain |

The schedule must be written, posted near the analyzer, and assigned to a named individual. Rotating responsibility without a written schedule reliably produces gaps. The schedule should also include calendar-based tasks: monthly review of control data, quarterly verification of pipette accuracy, and annual review of the entire program.

## Troubleshooting Out-of-Range QC Results

When a control result falls outside the established range, the first decision is whether to report patient results. The default position is to hold patient results until the problem is resolved. Exceptions exist for stat results with immediate clinical consequence, but these must be flagged as potentially compromised and repeated when the system is restored.

Work through the troubleshooting sequence in a fixed order. This prevents random component replacement and wasted time.

### Step 1: Rule Out Operator and Sample Error

Confirm the correct control lot was used and that the vial was not expired. Check that the control was reconstituted with the correct volume of the correct diluent and that it was used within its stated stability window. Verify the control was at room temperature before testing. A control vial left on the bench for hours or repeatedly warmed and cooled will drift.

### Step 2: Check the Analyzer State

Review the instrument log for error codes, incomplete cycles, or interrupted runs. Confirm the reagent pack has sufficient volume and has not expired. Check that the waste line is not full and the sample probe is clear. For hematology analyzers, verify the diluent and lyse reagents are in date and that the instrument passed its last background count.

### Step 3: Examine the Pattern of Failure

A single control level failing while the other passes suggests a problem near that concentration range. Both levels failing in the same direction suggests a systematic issue: reagent degradation, calibration drift, or temperature failure. Both levels failing in opposite directions suggests a matrix or interaction problem with the control material itself, often after a lot change.

### Step 4: Repeat the Control

Run a fresh aliquot from a newly opened control vial. If the repeat is in range, the original failure was likely a handling or stability issue. Document the event and continue. If the repeat is still out, proceed to calibration verification or instrument maintenance per the manufacturer protocol.

### Step 5: Escalate

If the problem persists after recalibration, contact the instrument manufacturer technical support. Document all steps taken, including dates, times, lot numbers, and results. This record is essential for identifying recurring failure patterns and for defending the quality of reported results if questions arise later.

A structured troubleshooting guide should be posted at each analyzer. It should include the most common failure modes for that specific instrument, the likely causes, and the corrective action. The [MSD Veterinary Manual](https://www.msdvetmanual.com/) provides species-specific reference information that can help determine whether a control failure is clinically significant for the patient population being tested.

## Documentation and Data Management

Every QC result must be recorded, whether in a paper log, spreadsheet, or laboratory information system. The record should include the date and time, operator initials, control lot number and expiration, instrument used, and the numeric result for each analyte. Levey-Jennings charts should be maintained for quantitative assays so that trends and shifts are visible before a control exceeds its range.

A trend is defined as six consecutive control values moving in the same direction. A shift is six consecutive values on one side of the mean. Both warrant investigation even when all values remain within the accepted range. These patterns often indicate reagent aging, gradual instrument drift, or a change in environmental conditions such as ambient temperature.

Review QC data monthly. Calculate the mean and standard deviation for each control level and compare them to the manufacturer's stated values. If your laboratory's mean differs consistently from the manufacturer's, this may reflect local conditions such as altitude, water quality, or reagent handling. Document the reason for any adjustment to the acceptable range.

## Species and Setting Considerations

The QC program must reflect the species being tested. A practice seeing predominantly dogs and cats can rely on commercial controls formulated for those species. A practice seeing exotic species, birds, or production animals must verify that the analyzer and reagents perform acceptably for those samples. Some analyzers have species-specific modes or algorithms, and the [American Society for Veterinary Clinical Pathology quality assurance guidelines](https://www.asvcp.org/page/QALS_Guidelines) address method validation for non-standard species.

Reference intervals are species-specific, and QC targets must be interpreted accordingly. A control value that falls outside the manufacturer's stated range may still be acceptable for a particular species if the laboratory has verified the method for that species. The converse also applies: a control value within the manufacturer's range may be unacceptable if the laboratory's own verified range for that species is narrower.

Production animal practice introduces additional considerations. Testing performed in the field with portable analyzers is subject to temperature extremes, vibration, and variable power supply. The QC schedule must account for these conditions. Controls should be transported and stored according to manufacturer specifications, and their performance verified at the point of use. The [World Organization for Animal Health terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) address quality assurance expectations for laboratories supporting animal health surveillance and trade, which may apply to practices performing regulatory testing.

Point-of-care instruments used in ambulatory practice require a different QC cadence than fixed laboratory analyzers. Verify control performance at the start of each day of field use, after any drop or impact, and after battery replacement. Document these checks in the same manner as in-clinic controls.

## When to Refer

A practice laboratory has limits. When QC failures cannot be resolved after systematic troubleshooting, when the analyzer requires repeated repair, or when the test volume does not justify the cost of maintaining a robust QC program, referral to a commercial veterinary laboratory is the appropriate choice. The decision to refer should be based on the laboratory's ability to produce reliable results, not on convenience or cost alone. The [American Veterinary Medical Association practice resources](https://www.avma.org/resources-tools) provide guidance on professional standards for in-house testing and referral relationships.

Similarly, some assays are better performed at reference laboratories regardless of in-house capability. Endocrine testing, therapeutic drug monitoring, and specialized coagulation panels typically require methods and quality controls that are not feasible in a practice setting. The QC burden for these assays rests with the reference laboratory, and the practice should verify that the laboratory participates in external quality assessment and can provide evidence of its own QC performance on request.

## Recognized Failure Modes and Early Detection

Quality control programs fail in predictable ways. The most common is the accumulation of unreviewed control data. A technician runs controls daily, the analyzer plots them, and nobody examines the trend until a patient result looks implausible. By then, the analyzer may have been producing biased results for days. Review control charts weekly, not monthly, and look at the pattern, also the last point.

The second failure mode is the control material itself. Lyophilised controls degrade after reconstitution, absorb moisture when opened, and vary between lots. A shift that coincides with a new control lot is usually a lot-to-lot difference, not an analyzer fault. Record lot numbers and reconstitution dates on every run. When changing lots, run old and new controls in parallel for at least five days to establish the new baseline.

The third failure mode is matrix mismatch. Control material is not patient sample. Some analyzers handle animal blood differently from human-based controls, particularly for platelet counts and hematocrit. A control within range does not guarantee that patient samples are accurate. This is why method validation with species-specific samples matters, and why external quality assessment with veterinary-specific schemes is essential.

The fourth failure mode is selective reporting. Laboratories that record only the controls that pass, or repeat controls until they pass and then record the passing result, destroy the statistical basis of QC. The control result is a random draw from the analyzer's current performance. Discarding draws because they are inconvenient is not QC, it is record keeping.

## Common Errors and Corrective Action

Less experienced staff make characteriztic mistakes. They run controls at the wrong time, for example only after calibration or after a service visit, instead of at the start of each patient run. They place controls in the wrong position in the run, for example at the end, so that a drift developing during the run is missed. They use expired controls, or controls that have been left at room temperature overnight.

The corrective action is procedural. Write the QC schedule into the standard operating procedure, specify the position of controls in the run, and train staff to check expiry dates and storage logs before each run. A simple rule helps: if the control was not stored correctly, the result does not count, and the run should be repeated.

A second common error is misinterpreting a single out-of-range control as an analyzer failure. A single 1:2s violation, where one control exceeds two standard deviations, has a false alarm rate of roughly 5% per control per run. With two controls per run, the chance of at least one such violation by chance alone is near 10%. The response should be to examine the other control, check the pattern, and repeat if needed. Only a 1:3s violation, where one control exceeds three standard deviations, or two consecutive controls on the same side of the mean, warrants immediate troubleshooting.

A third error is failing to document corrective actions. The record should show what was checked, what was found, and what was done. Without this, the next shift cannot tell whether a problem was resolved or merely ignored.

## Limitations of the Evidence and Areas of Expert Disagreement

The evidence base for veterinary laboratory QC is thinner than for human laboratory medicine. Most published work comes from human clinical laboratories, and the transferability of specific rules and thresholds to veterinary analyzers is assumed instead of proven. The ASVCP guidelines provide a structured framework, but they are consensus guidance, not trial-derived evidence, and they acknowledge that some recommendations rest on expert opinion [ASVCP quality assurance and laboratory standards guidance](https://www.asvcp.org/page/QALS_Guidelines).

Expert opinion differs on several points. The frequency of internal QC is one. Some authorities recommend controls with every run, others accept daily controls for stable analyzers, and a few argue that weekly controls suffice for low-throughput point-of-care devices. The correct answer depends on the analyzer, the species mix, and the clinical consequences of an error. A practice running sick feline patients on a coagulation analyzer should control more frequently than a practice running routine canine wellness panels.

Another area of disagreement is the acceptable performance of point-of-care devices. These instruments trade analytical precision for speed and convenience. Some experts argue that the clinical benefit of immediate results outweighs the reduced precision, while others maintain that any result used for treatment decisions should meet the same standards as a reference laboratory result. The practitioner must decide where the threshold lies for each test and each clinical context.

A further limitation is the scarcity of published data on the performance of veterinary medicines and reagents. A regulatory study of veterinary medicines in Ethiopia found that 6.9% of tested products failed assay specifications, with 60 samples below the minimum limit [quality survey of veterinary medicines in Ethiopia](https://pubmed.ncbi.nlm.nih.gov/35241169/). This finding, from one country's regulatory program, illustrates that product quality cannot be assumed. It also shows why batch verification and external assessment matter, and why the evidence base for veterinary product quality is uneven across regions.

## When to Refer, Escalate, or Report

Referral is appropriate when the problem exceeds the practice's capacity. If the analyzer fails repeated controls, if the pattern suggests a hardware fault, or if the practice cannot identify the cause of a persistent shift, contact the manufacturer's technical support or the laboratory that services the instrument. Do not continue running patient samples on an analyzer that cannot produce in-range controls.

Specialist consultation is warranted when QC results suggest a method problem that affects a particular species or analyte. A veterinary clinical pathologist can advise on whether a control shift reflects a genuine analyzer problem or a matrix effect specific to the species being tested. This is particularly relevant for exotic species, where control materials may not exist and where method validation data are sparse.

Regulatory reporting applies to specific circumstances. If a quality control failure suggests that a batch of veterinary medicines or biological products is defective, the manufacturer and the relevant regulatory authority should be notified. The World Organization for Animal Health sets international standards for veterinary product quality and surveillance, and practitioners should be aware of the reporting pathways in their jurisdiction [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/). Reporting requirements differ between countries, and the practitioner should know the local pathway before a crisis occurs.

| Observation | Likely cause | Discriminating check |
|---|---|---|
| Single control exceeds 2 SD | Random chance | Check other control, repeat once |
| Both controls exceed 2 SD on same side | Calibration drift | Recalibrate, run fresh controls |
| Shift after new control lot | Lot-to-lot difference | Run old and new lots in parallel |
| Trend across several days | Reagent or sensor deterioration | Check reagent expiry, run calibration verification |
| One analyte out, others in range | Reagent or cuvette problem for that channel | Replace reagent, check for clots or bubbles |
| Controls pass, patient results implausible | Matrix mismatch or species effect | Run patient sample on reference analyzer |

## Frequently Asked Questions

### How Do I Build a Meaningful QC Program When My Practice Has a Tight Budget?

Prioritize internal quality control for the tests you run most often and that drive the highest-risk clinical decisions. A single daily level of control for a hematology analyzer is more valuable than no control at all, but you must document the limitation. External quality assessment participation is non-negotiable even on a small budget, because it is the only way to detect systematic bias that internal controls cannot reveal. The [American Society for Veterinary Clinical Pathology quality assurance guidelines](https://www.asvcp.org/page/QALS_Guidelines) provide tiered recommendations that scale with laboratory complexity. Consider sharing EQA enrollment with nearby practices or using regional laboratory cooperatives to reduce per-practice costs while maintaining independent result comparison.

### What Should I Do When My Practice Cannot Afford a Commercial Control Material?

Commercial controls are preferred because their assigned values are validated across many instruments, but a carefully prepared in-house pool can serve as an interim substitute. Use surplus patient samples with normal and abnormal values, aliquot them into single-use vials, and store them under the same conditions as patient samples. Establish your own target mean and acceptable range from at least 20 runs over several weeks. This approach cannot detect lot-to-lot reagent shifts as reliably as commercial controls, so flag any change in control mean after reagent lot changes. Document the preparation date, expiry, and storage conditions for every aliquot. The [MSD Veterinary Manual](https://www.msdvetmanual.com/) notes that in-house laboratory quality depends on consistent technique, which becomes more critical when control materials are non-standardized.

### How Does QC Differ for a Reference Laboratory Versus a Practice Point-of-Care Instrument?

Reference laboratories operate under continuous quality management with multiple control levels per shift, daily calibration verification, and mandatory EQA enrollment. Point-of-care instruments in practice settings require a pragmatic adaptation: run at least one control level each day of use, verify the control lot against the instrument after every reagent lot change, and perform EQA at least twice yearly. The critical difference is the consequence of failure. A reference laboratory can quarantine results and repeat testing before release, while a practice instrument often produces results that are acted upon immediately. This means the practice must have a lower threshold for repeating patient samples when control values drift toward the edge of the acceptable range, even before they exceed it. The [AVMA practice resources](https://www.avma.org/resources-tools) emphasize that point-of-care testing oversight is part of professional responsibility.

### When Should I Repeat a Patient Sample Because of QC Concerns instead of Accept the Result?

Repeat the patient sample when any control value falls outside two standard deviations from the established mean, when a control shows a trend across three consecutive runs, or when the patient result is clinically unexpected and the analyzer flags a warning. Also repeat when the patient result falls near a clinical decision threshold, such as a platelet count near the transfusion trigger or a glucose value near the hypoglycemic range. If the repeat result agrees with the first within the analyzer's stated repeatability, the result is likely reliable. If the repeat differs substantially, suspect a clot, analyzer drift, or sample degradation. The [evaluation of the Cell-Dyn 3500 in extreme values](https://pubmed.ncbi.nlm.nih.gov/7971261/) demonstrated that linearity and repeatability can degrade at very high or low cell concentrations, so exercise particular caution with extreme patient values.

### How Should I Explain a QC Failure to a Client Whose Pet's Results Are Affected?

Be direct and factual without overstating the risk. Explain that the laboratory runs quality checks on the analyzer each day, that today's check fell outside the acceptable range, and that the practice is repeating the affected tests to ensure accuracy. Do not speculate about the cause until the investigation is complete. Offer a concrete timeline for when the repeated results will be available. If the QC failure occurred before the patient's sample was run, the initial results may still be valid, but the practice should confirm this by repeating the sample after the analyzer passes QC. The [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) emphasize that transparency in diagnostic processes supports trust in veterinary services, and the same principle applies at the individual practice level.

### What Records Must I Keep for QC, and for How Long?

Maintain a permanent log of every control run, including date, time, operator, control lot number, instrument readings, and any corrective action taken. Record reagent lot numbers and their dates of first use. Document all EQA submissions, results, and any follow-up investigations. Keep calibration and maintenance records separate from daily QC logs but cross-reference them when troubleshooting. Retention periods vary by jurisdiction and accreditation body, but a minimum of two years is a reasonable baseline for practice records, while longer retention is advisable for controlled substances testing or medicolegal cases. The [quality control laboratory study of veterinary medicines in Ethiopia](https://pubmed.ncbi.nlm.nih.gov/35241169/) illustrates that systematic documentation of quality failures is essential for identifying recurring problems, a lesson that applies equally to practice laboratories.

## Related Clinical & Scientific Guides

* [Peripheral Blood Smear Evaluation: A Step-by-Step Guide](/knowledge/veterinary-medicine/clinical-pathology/peripheral-blood-smear-evaluation-guide)
* [Reticulocyte Counts in Veterinary Medicine: Clinical Utility and Interpretation](/knowledge/veterinary-medicine/clinical-pathology/reticulocyte-counts-veterinary-medicine)
* [Cerebrospinal Fluid Analysis in Veterinary Neurology: Collection and Interpretation](/knowledge/veterinary-medicine/clinical-pathology/cerebrospinal-fluid-analysis-veterinary)


## References and Further Reading

- [Applicability of the Monocyte Activation Test (MAT) for hyperimmune sera in the routine of the quality control laboratory: Comparison with the Rabbit Pyrogen Test (RPT).](https://pubmed.ncbi.nlm.nih.gov/26688320/). 2016.
- [Study on identification, assay and organoleptic quality of veterinary medicines in Ethiopia.](https://pubmed.ncbi.nlm.nih.gov/35241169/). 2022.
- [Study of LAL and Recombinant Cascade Reagents Methods for Bacterial Endotoxin Testing in Pharmaceutical Products.](https://pubmed.ncbi.nlm.nih.gov/41844320/). 2026.
- [[Evaluation of Cell-Dyn 3500 in extreme values].](https://pubmed.ncbi.nlm.nih.gov/7971261/). 1994.
- [Abstract 18 Developing a Potency Assay for Cord Tissue MSCs](https://europepmc.org/article/PMC/PMC9446954). 2022.
- [American Society for Veterinary Clinical Pathology Guidelines](https://www.asvcp.org/page/QALS_Guidelines). American Society for Veterinary Clinical Pathology.
- [MSD Veterinary Manual, Professional Edition](https://www.msdvetmanual.com/). MSD Veterinary Manual.
- [American Veterinary Medical Association Practice Resources](https://www.avma.org/resources-tools). American Veterinary Medical Association.
- [WOAH Terrestrial Animal Health Code](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/). WOAH.

## Related Articles

- [Coagulation Testing in Veterinary Medicine: A Practical Guide](/knowledge/veterinary-medicine/clinical-pathology/coagulation-testing-veterinary-practical-guide)
- [Laboratory Monitoring of Anemia: Reticulocyte Response and Beyond](/knowledge/veterinary-medicine/clinical-pathology/laboratory-monitoring-anemia-reticulocyte)
- [Preanalytical Errors in Veterinary Laboratory Testing: Prevention and Troubleshooting](/knowledge/veterinary-medicine/clinical-pathology/preanalytical-errors-veterinary-laboratory)
- [Serial Fecal Testing for Monitoring Parasite Control Programs](/knowledge/veterinary-medicine/clinical-pathology/serial-fecal-testing-monitoring-parasite-control-programs)
- [Point-of-Care Testing in Veterinary Practice: Benefits and Limitations](/knowledge/veterinary-medicine/clinical-pathology/point-of-care-testing-veterinary)

> This article is educational professional reference material for veterinary audiences. It is not a substitute for veterinary diagnosis, individual clinical judgment, current product labeling, or applicable regulatory requirements.