Proficiency Testing Failure for Glucose in a Resource-Limited Chemistry Laboratory
A 210-bed community hospital laboratory reports a proficiency testing (PT) failure for glucose on its sole chemistry analyzer. Three of five PT challenges exceed the acceptable range, all on the high side; the other two are within range but near the upper limit. The analyzer's twice-daily QC has been within acceptable limits for the past month, but only one level is run on weekends because of staffing shortages. A new reagent lot was placed on the analyzer 18 days ago, and the calibration was repeated at that time. The laboratory director also learns that the night shift has been using expired linearity material for calibration verification. The PT kit was handled by a generalist who normally works in hematology, and the results were not reviewed by the chemistry supervisor before submission. The next PT event is in 6 weeks.
1. What are the most likely causes of the PT failure, and what investigation should the laboratory perform?
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The failure is systematic rather than random because all three failures are on the high side and the two passing results are near the upper limit. That pattern points to a calibration or reagent-lot problem, a pipetting or dilution error, or a temperature/water issue rather than isolated random error. The new reagent lot placed 18 days earlier is a prime suspect, especially because calibration was repeated at that time and calibration verification used expired linearity material. Weekend one-level QC could allow a shift to go undetected. The generalist handling the PT kit without supervisor review raises concern for a handling or transcription error. Investigate reagent lot validation records, calibration curves, linearity data, QC logs, analyzer temperature and water quality, pipette calibration, and the raw PT result files. Review whether the PT samples were reconstituted or stored correctly. Do not simply repeat the PT; document the root-cause analysis.
2. What corrective actions and regulatory notifications are required?
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The laboratory must investigate the unacceptable PT performance, document corrective action, and retain records as required by its accreditation program. Corrective actions include recalibrating with valid materials, performing calibration verification with nonexpired linearity material, evaluating and possibly replacing the new reagent lot, running two levels of QC daily including weekends, and retraining staff on PT handling and supervisor review. Review all patient glucose results since the suspected shift and assess whether corrective action is needed, including possible re-collection or amended reports if clinically indicated. Notify the laboratory director and quality manager, and follow the accreditation program's PT failure policy. Do not send PT samples to another laboratory or alter results. If the failure represents a serious quality problem, the laboratory may need to report it through its quality system and take immediate action to prevent patient harm.
3. What process changes would reduce the risk of recurrence before the next PT event?
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Implement two-level QC every day, including weekends, and require documented review before patient results are released. Strengthen reagent-lot validation and calibration verification with nonexpired materials, and schedule linearity checks on a defined timeline. Assign PT handling only to trained staff, with mandatory supervisor review of results and raw data before submission. Audit pipetting, sample reconstitution, and storage practices. Use trend review of QC and patient results to detect shifts earlier. Document competency assessments and corrective actions, and present the case at a quality meeting. These steps address the system failures rather than blaming the individual generalist.