Internal Quality Control Failure Before a Renal Unit Run
In the chemistry section of a private hospital laboratory in Nairobi, you are the quality officer. The laboratory uses two levels of lyophilised IQC material for creatinine and ALT on a dry chemistry analyser. The current QC lot was validated three months ago: creatinine level 2 mean 1.80 mg/dL, SD 0.06. On Monday morning, level 2 creatinine is 2.01 mg/dL and ALT level 2 is 1.9 SD above its mean; the Levey–Jennings chart shows the last five creatinine points all above the mean. A new lot of creatinine reagent was opened on Friday, and the analyser was serviced on Thursday with a lamp replacement. The laboratory has 23 inpatient samples waiting, including six from the renal unit. The section head says the QC is “only slightly out” and wants results released with a comment. The hospital has no written QC release policy for this analyser.
1. Apply the QC rules to the data and decide whether patient results may be released. Show your reasoning.
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The run should be rejected; patient results should not be released.
Creatinine level 2: 2.01 − 1.80 = 0.21 mg/dL; 0.21 ÷ 0.06 = 3.5 SD. This exceeds the 1_3s rejection rule, so the run is out of control. In addition, five consecutive points above the mean indicate a shift or trend, which is a systematic error pattern and should trigger investigation even if no single point breached 1_3s.
ALT level 2 at +1.9 SD does not breach 1_3s on its own, but it does not rescue the run. When one analyte on a shared analyser fails, the run is rejected until the cause is corrected and QC is repeated.
A comment on the report does not make an invalid result valid. The section head’s “slightly out” framing is not a defensible release criterion. Hold the 23 samples, notify the clinician in charge of the renal unit that results will be delayed, and repeat QC after corrective action. If a clinically urgent result cannot wait, the laboratory should use an alternative validated method or refer the sample, and document the decision. The absence of a written release policy is itself a nonconformity; draft and approve one.
2. What root-cause investigation would you carry out, and in what order?
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Use a structured approach, starting with the most likely and most easily checked causes.
- QC material: check reconstitution date, storage, expiry, vial handling and whether the control was properly mixed. A deteriorating or wrongly reconstituted control can mimic a shift.
- Reagent lot: the new creatinine reagent lot opened on Friday is a prime suspect. Check lot number, expiry, storage, on-board stability, and whether lot-to-lot verification was performed before use. Compare with the previous lot if still available.
- Analyser service: the lamp replacement on Thursday could affect photometry, calibration or wavelength checks. Review the service report, calibration status, lamp hours, cuvette or flow-cell condition and temperature.
- Calibration: was the analyser recalibrated after the lamp change, and did calibration pass? Check calibration drift and slope.
- Operator and environment: pipetting technique, water quality, timing, and room temperature.
- Data review: plot the Levey–Jennings chart and check whether the shift began before or after the reagent lot change or service.
Run a fresh vial of QC, repeat the level 2 control, and if the failure persists, recalibrate and repeat. If the new reagent lot is implicated, perform lot comparison against the old lot. Document each check, the findings and the conclusion. Do not simply repeat QC until it passes without identifying the cause.
3. What corrective actions and documentation should follow, and how would you prevent recurrence?
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Corrective actions depend on the root cause, but the sequence is consistent.
- Stop reporting. Quarantine or segregate the suspect reagent lot if implicated.
- Repeat QC with a fresh control vial. If the fault is calibration-related, recalibrate and repeat both levels.
- If the new reagent lot is at fault, reject it, inform the supplier, and revert to a verified lot.
- If the analyser is at fault, call the service engineer and document the intervention.
- Once QC is within acceptable limits, rerun patient samples and release results with the correct turnaround time.
- Review any results already released since the shift began; if affected, initiate a look-back and inform clinicians.
Documentation: a nonconformity report with the QC values, rule violated, investigation, root cause, action taken, date, and person responsible. Record the delay and clinician notification. Update the QC chart and the reagent lot log.
Prevention: write and approve a QC release policy that names the Westgard rules, the action to take on rejection, who may authorise release, and how urgent samples are handled. Add lot-to-lot verification and post-service calibration checks to the equipment maintenance procedure. Train staff on the policy and audit compliance monthly. The section head’s willingness to release “with a comment” should be addressed directly through the quality committee, because it is a culture problem as much as a technical one.