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When a laboratory instrument produces drifting controls, disagreement between replicates, or unexpected run-to-run differences, pause and determine whether the analytical process is in control before releasing more results. If an internal quality-control result is outside its acceptable range, stop testing, withhold patient results, investigate the entire testing system, correct the cause under the laboratory’s procedures, and verify acceptable controls before repeating patient samples. Do not treat repeated testing as a diagnosis.
The instrument is only one possible cause. Sample condition, collection and storage, reagents, control material, calibration, utilities, software, operator technique, current instructions, maintenance, and the equipment itself can all create inconsistent results. Use the instrument manual, method SOP, internal QC procedure, and applicable local requirements for the exact response; general guidance cannot replace an instrument-specific troubleshooting process.
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First decide whether testing is in control
Define the signal precisely. Inconsistency may appear as a gradual drift in control or calibrator values, an unexpected difference between replicates, a sudden change between runs, or an obvious instrument malfunction. A single implausible patient result can be the first visible sign, but control trends often show a developing problem earlier.
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When controls are outside the laboratory’s acceptable range, treat the testing process as out of control. The World Health Organization (WHO) quantitative quality-control guidance states: “Patient results must not be reported until the problem is resolved and the controls indicate proper performance.” Stop the affected testing, place results on hold, and follow the laboratory’s authorization and notification rules. Do not release a result merely because it appears clinically plausible.
If controls are in range but patient replicates or runs disagree, do not assume the instrument is cleared. Confirm that the controls are appropriate for the method and that the observed discrepancy is real under the laboratory’s validation and review criteria. The exact threshold for declaring an instrument inconsistent is method- and procedure-specific; there is no universal cutoff that applies to every technology.
What to check before repeating a run
Before rerunning patient material, record the symptoms and perform a focused check. Use the manufacturer’s troubleshooting flowchart where available, and change one thing at a time so that each check has an interpretable result.
- Record the run date and time, instrument identification, method, software or procedure version, operator, control values, calibrator values, reagent and control lots, calibration status, error messages, and relevant maintenance or environmental observations.
- Confirm that the sample identity, container, volume, anticoagulant or additive, collection time, transport conditions, storage temperature, and time limits meet the method SOP.
- Inspect the sample for features that the method identifies as potentially interfering, such as clotting, hemolysis, lipemia, contamination, insufficient volume, evaporation, or an unsuitable matrix.
- Check reagent and control expiration dates, storage temperatures, open-vial or onboard stability, preparation and reconstitution records, contamination, and lot changes.
- Verify that calibration is current, that a new reagent lot received any required lot-specific calibration or verification, and that calibration checks have passed.
- Review instrument status, maintenance due dates, function checks, alarms, temperature or pressure readings, fluid levels, consumables, and any recent service or software change.
- Check electrical power, water, gas, ventilation, room temperature, humidity, and other utilities required by the instrument.
- Confirm that the operator followed the current method instructions, including mixing, pipetting, loading, incubation, timing, dilution, and result-review steps.
- Look for a pattern: does the failure follow one instrument, one reagent or control lot, one operator, one sample type, one time period, or all testing? Use the pattern to organize the investigation, not as a validated diagnosis by itself.
Do not repeatedly process the same sample while changing several settings, replacing multiple reagents, and recalibrating simultaneously. That can conceal the original cause and make the run history difficult to interpret.
Is the problem related to a poor sample?
Yes, it may be. WHO equipment troubleshooting guidance specifically asks whether the sample was collected and stored correctly and whether sample characteristics could affect performance. Verify identification and chain of custody, transport and storage conditions, specimen age, required mixing, container type, volume, and method-specific interference criteria. A sample problem is more likely when the discrepancy is limited to one specimen or specimen type, but that pattern does not prove the instrument is functioning correctly.
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Investigate the whole testing system
WHO quality-control guidance identifies several possible contributors: degraded reagents or kits, degraded control material, operator error, failure to follow instructions, an outdated procedure manual, equipment failure, and calibration error. These are investigation leads, not proof that a particular factor caused the discrepancy.
Samples and pre-analytical conditions
Confirm that collection devices, preservatives, transport containers, and storage conditions match the method. Check whether the sample was exposed to excessive time, temperature, light, agitation, freeze-thaw cycles, or contamination. Determine whether the instrument or method requires a minimum volume, a specific mixing step, centrifugation, filtration, dilution, or removal of interfering material. If the specimen is unsuitable, follow the rejection and recollection procedure rather than forcing a repeat on compromised material.
Reagents, calibrators, and controls
Inspect physical condition as well as the printed expiry date. A material can be unusable because of incorrect storage, repeated warming, evaporation, contamination, failed reconstitution, or exceeded open-vial stability. Compare the lot and preparation records with the method instructions. A new lot may require calibration, parallel testing, verification, or a documented acceptance decision before routine use. Check that control material was reconstituted, mixed, aliquoted, and stored as specified.
Calibration and instrument settings
Review calibration history, calibration curves or factors where the system provides them, verification results, and any failed or bypassed prompts. Confirm that the active assay, units, reference settings, dilution factors, flags, and operator-selected parameters are correct. Do not apply a recalibration, reset, cleaning cycle, or software change unless the instrument instructions or laboratory procedure authorizes it and the action is documented.
Utilities, environment, and software
Check power interruptions, voltage or backup supply alarms, water quality and pressure, gas supply, waste capacity, temperature, humidity, ventilation, and network or middleware changes. Review instrument logs for alarms, communication failures, temperature excursions, blocked probes, aspiration errors, mechanical faults, or software updates. A utility or software problem can affect more than one assay and may explain a change that appears unrelated to a particular sample.
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Operator technique and current instructions
Confirm that the operator used the current controlled procedure, completed required warm-up and function checks, loaded materials in the correct positions, observed timing and mixing requirements, and reviewed flags before accepting results. Check whether a procedure manual or quick-reference instruction is outdated. If a technique issue is identified, correct it through the laboratory’s training and competency process rather than relying on an informal reminder.
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Apply the corrective action supported by the instrument manual, method SOP, and internal QC procedure. Depending on the evidence, that may involve replacing compromised material, correcting a storage problem, restoring a utility, completing authorized maintenance, correcting a setting, updating an instruction, or obtaining qualified technical service. Do not claim that a particular cleaning, repair, or recalibration is appropriate without instrument-specific support.
After the action, re-check the relevant control material and document the result. WHO guidance directs staff to identify and correct possible causes, re-check controls, and only then repeat patient samples along with another control when controls indicate proper performance. The repeat run should be linked to the original run in the laboratory information system or controlled worksheet, with the reason, corrective action, control evidence, and authorization recorded.
If controls remain unacceptable, keep patient results on hold and continue the investigation or escalate it. If controls are acceptable but a patient result remains discordant, follow the method’s review, dilution, confirmatory, repeat-collection, or referral procedure. A passing control does not eliminate the need to investigate a specimen-specific problem or a method limitation.
Choose the next action based on evidence
| Observed situation | Immediate status | Next action | When qualified service or an alternative route is needed |
|---|---|---|---|
| Controls are out of range and a cause is not yet established | Stop affected testing; withhold results | Review trends, sample, materials, calibration, utilities, technique, and equipment one change at a time | Escalate if the cause is unresolved or the SOP does not authorize the corrective action |
| Controls are out of range and a correctable material, setup, or procedural issue is identified | Keep results on hold during correction | Correct under the SOP, re-check controls, and document verification | Use technical help if the correction requires service access or specialized diagnosis |
| Controls are in range but one sample is unsuitable or interferent | Do not report the affected result without the required review | Follow specimen rejection, recollection, dilution, or confirmatory procedures | Use another testing route if the method cannot validly handle the specimen |
| Evidence points to an equipment fault | Remove the instrument or affected function from routine use | Label it out of service, preserve logs, estimate the impact, and arrange repair | Use the manufacturer or another qualified technical expert; do not perform unauthorized repairs |
| Instrument service will interrupt testing | Inform authorized users of possible delays | Use a validated backup instrument, replacement instrument, or referral laboratory if available | Confirm method comparability, authorization, specimen stability, and reporting arrangements before transfer |
Assess whether earlier results may be affected
An instrument can produce a plausible-looking result while operating incorrectly. If a defect is suspected, do not limit the review to the current run. WHO Laboratory Quality Management System guidance recommends taking apparently defective equipment out of service, arranging repair, estimating the defect’s potential influence, deciding whether samples need retesting, determining when the malfunction began, and tracing potentially affected samples.
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Define the review window
Use the earliest reliable evidence of the problem: the first failed or drifting control, the last acceptable function check, an alarm or maintenance event, a calibration change, or a service report. The window may differ by assay if the fault affects only a module, channel, temperature zone, probe, detector, or software function. Record why the chosen start and end points are reasonable.
Identify potentially affected testing
Query the instrument and laboratory information system for tests performed during the window. Stratify the review by assay, specimen type, instrument channel, reagent and calibration lot, control behavior, result flags, and retained specimen availability. Compare affected results with control trends, repeat testing, an alternative validated method, or clinical information only where the laboratory’s procedure permits that comparison. Do not assume every result in the period is wrong, and do not assume that a single acceptable control clears every prior result.
Decide on retesting and communication
The decision depends on the fault, method performance, time window, affected tests, specimen stability, retained samples, and local requirements. Retest specimens when the documented impact assessment and procedure indicate that it is necessary and technically valid. If specimens are no longer held, WHO guidance says to contact the relevant clinicians or patients as applicable. Follow authorized privacy, notification, correction, and amended-report procedures; communication should be proportionate to the assessed risk and supported by the laboratory’s quality system.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Remove faulty equipment from service safely
WHO equipment guidance is explicit: “Do NOT use faulty equipment! Seek help from the manufacturer or other technical expert.” Label the instrument clearly as out of service, prevent accidental use in the scheduling or information system, preserve error logs and control data, and record the date, observed symptoms, affected tests, and person who authorized the shutdown. If only one function is affected, the laboratory should document whether the remaining functions are independently verified for use; do not infer partial safety without evidence.
Check warranty and service documentation before opening covers, bypassing interlocks, modifying firmware, or attempting repairs beyond authorized routine maintenance. The laboratory should know who is qualified to service the model, what information the service provider needs, and which post-repair calibration, verification, or performance checks are required before release back to testing.
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Maintain continuity while the issue is unresolved
Possible continuity routes include a validated backup instrument, a replacement instrument during repair, or referral of samples to a nearby laboratory. Availability is laboratory- and service-dependent, so confirm the practical details before promising turnaround times.
- Verify that the alternative method or instrument is approved for the test, specimen type, reportable range, units, reference intervals, and clinical use.
- Check whether a comparison, calibration verification, parallel run, or medical-director authorization is required before reporting.
- Confirm specimen stability, packaging, transport temperature, chain of custody, and referral-laboratory acceptance criteria.
- Tell affected clinical users about likely delays through the laboratory’s approved communication route.
- Record which results were produced by the alternative route and retain the associated control and method documentation.
Document the investigation so it can be reconstructed
A useful record connects the symptom to the equipment, materials, decisions, and verification evidence. Follow the laboratory’s controlled-document and record-retention procedures.
- Equipment name, type, model, unique asset label, serial number, manufacturer, service contacts, location, and status.
- Date and time of the discrepancy, affected method and samples, instrument logs, alarms, control and calibrator results, and trend history.
- Reagent, calibrator, and control lot numbers; expiration, storage, preparation, and open-vial information.
- Calibration, maintenance, function-check, repair, software, utility, and environmental records relevant to the event.
- Investigation questions, checks performed, one-change-at-a-time observations, suspected cause, corrective action, and who authorized each decision.
- Post-correction control results, verification or comparison data, release-to-service approval, and any affected-result review or notification.
WHO Laboratory Quality Management System guidance describes an equipment register that can include the equipment name, type and model, unique label, serial number, manufacturer and contacts, purchase and service dates, location, condition, service provider, maintenance frequency, prior and scheduled maintenance, and remarks. A paper or digital maintenance and calibration logbook can help organize these fields, but it does not replace controlled laboratory records, the SOP, or the quality-management system. When equipment has a critical effect on testing and is nonfunctional, the guidance says to put it out of service and arrange repair.
How CLSI QMS23 fits into an equipment program
CLSI QMS23-Ed2, General Laboratory Equipment Performance Qualification, Use, and Maintenance, was published June 19, 2019. Its scope covers performance qualification, routine function checks, calibration verification, and preventive maintenance for 20 types of general laboratory equipment. Examples include centrifuges, fume hoods, and pipettes. It does not cover specialized instrumentation exclusive to particular laboratory sections, and its recommendations supplement rather than replace manufacturer instructions.
That scope makes QMS23 useful when a laboratory is building an installation-to-retirement equipment program or standardizing records for general equipment. It is not a substitute for the troubleshooting manual and validated method procedure for a specialized analyzer. Kathleen A. Grindle, MT(ASCP), CQA(ASQ)CPGP, vice-chairholder of QMS23, described the document’s structure this way: “Each equipment section in the guidance has the same organizational structure for ease of use but is specific for a particular piece of equipment. Essentially, a lab can take a specific section and associated appendixes and create an installation to retirement protocol for that piece of equipment.”
When the investigation is complete
Close the event only when the laboratory has evidence that the process is back under control, the equipment or method has been appropriately verified, affected results have been assessed, and required reports or notifications are complete. The final record should state what was observed, what was ruled in or out, what corrective action was taken, why testing was resumed, and who approved the decision. If the cause remains uncertain, document the uncertainty and the additional monitoring or service plan rather than declaring the instrument repaired without evidence.
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