Two Consecutive Proficiency Testing Failures for Glucose
Northside Clinical Laboratory performs glucose and hemoglobin A1c testing under a Certificate of Compliance. In the first proficiency testing event of the year, the glucose result reported to the PT provider was 152 mg/dL, but the instrument printout showed 118 mg/dL; the technician had transcribed the wrong value. The laboratory discovered the error after submission and asked the PT provider to change the result; the provider refused. In the second event, glucose was again unsatisfactory because the analyzer had not been calibrated after a reagent lot change. The laboratory director wants to drop glucose from the test menu before the PT provider's next event to avoid a second consecutive failure and asks whether the laboratory can continue reporting patient glucose results while it investigates. The laboratory also plans to use the PT samples to verify the new lot of reagents.
1. Did the transcription error constitute a PT failure, and could the laboratory correct the PT result after submission? Explain.
Read the worked answer
Yes, it is a PT failure. PT evaluates the result the laboratory reports, not the result it intended to report. The laboratory reported 152 mg/dL and the peer result was 118 mg/dL, so the event is unsatisfactory regardless of the cause.
The laboratory could not correct the result after submission. PT rules prohibit changing PT results after the event and prohibit referring PT samples or communicating about them with other laboratories. Asking the provider to revise the result does not cure the failure and can itself raise a PT compliance concern.
The correct response is to treat the transcription error as a laboratory error, investigate why the result was transcribed incorrectly, document corrective action, and prevent recurrence. The failure remains part of the laboratory's PT record.
2. What are the required elements of the laboratory's investigation and corrective action for the two unsatisfactory glucose events?
Read the worked answer
The laboratory must investigate both events and document a corrective action plan that addresses root causes, not just the final numbers.
For the transcription error:
- Review the result-entry and reporting process.
- Determine whether a transcription step, manual entry, or lack of verification caused the error.
- Retrain staff and add a second check or interface safeguard.
For the calibration/reagent lot failure:
- Review calibration records and the reagent lot change procedure.
- Determine why calibration was not performed after the lot change.
- Repeat calibration and verify performance with controls and, where appropriate, patient comparison.
- Review patient results reported during the affected period for possible error.
Overall corrective action should include:
- A written investigation with root cause.
- Correction of the immediate problem.
- Verification that glucose testing is accurate before resuming reporting.
- Review of patient results since the last acceptable QC/calibration.
- Staff training and monitoring.
- Documentation of all actions for the PT file and surveyor review.
3. What are the regulatory consequences of two consecutive unsatisfactory PT events for glucose, and can dropping glucose from the menu avoid them?
Read the worked answer
Two consecutive unsatisfactory PT events for glucose constitute unsuccessful PT performance and can lead to suspension or limitation of the laboratory's certificate for that testing. The laboratory may be required to stop performing glucose testing, demonstrate accuracy, and successfully complete PT before resuming.
Dropping glucose from the menu after the failures does not erase the failures. The laboratory performed the testing, reported PT results, and failed. A menu change may affect future PT enrollment, but it does not retroactively eliminate sanctions. The laboratory should not use a menu change as a way to avoid the PT consequence.
A better response is:
- Stop glucose reporting if required by the sanction or until accuracy is established.
- Complete the investigation and corrective action.
- Notify the state agency/CMS as required and respond to any suspension or directed plan.
- Re-establish accuracy through calibration, QC, and successful PT or other required evaluation.
- Document patient-result review and communication with clinicians where indicated.
The laboratory also should not use PT samples for reagent-lot verification. PT samples must be tested as patient samples and cannot be used to satisfy routine verification needs.