How to investigate poor performance in proficiency testing

Investigating Poor Performance in Proficiency Testing

Significance of the topic

Proficiency testing (PT) is a key external quality assurance mechanism used to verify laboratory competence, comparability of results and suitability of methods. A poor PT outcome signals potential weaknesses in analytical practice, data handling or the chosen PT scheme and therefore requires a prompt, documented investigation. Effective management of unsatisfactory PT performance limits risk to clients, prevents recurrence, protects accreditation status and can save time and resources by targeting corrective actions efficiently.

Aims and overview of the guidance

This guidance outlines a pragmatic approach for laboratories to investigate unsatisfactory or questionable PT results, decide on corrective actions, document findings and verify effectiveness. It emphasises a stepwise root-cause approach that scales with the importance and frequency of problems and encourages interaction with PT providers when scheme issues are suspected.

Methodology and instrumentation used

The guidance recommends a systematic review of available evidence rather than prescribing specific instruments. Typical elements to inspect include:

• Raw analytical data and instrument output files
• Internal quality control (IQC) records and control charts
• Previous PT results and trend analysis across rounds
• Laboratory information management system (LIMS) records, data transfer and unit-conversion settings
• Test procedures, version history and training records
• Environmental and operational parameters (e.g., incubation temperature/time where microbiology is relevant)

If instrument or equipment failures are suspected, examine maintenance logs, calibration certificates and operator records. Where method performance is unclear, review validation documentation.

Main findings and discussion

Key operational recommendations and diagnostic steps are:

1. Analyse raw data, IQC performance and participant distributions for that PT round to contextualise the deviation.
2. Follow a stepwise root-cause investigation (examples: Fishbone diagram, 5 Whys) involving the analyst(s) and management as appropriate.
3. Identify whether the cause is clerical, technical (method or execution), or related to the PT scheme or PT items themselves.
4. After identifying likely causes, develop and document a corrective-action plan and evaluate whether previous patient or sample results might be affected.
5. Implement corrective actions, record them and monitor subsequent PT rounds and IQC to confirm effectiveness.

Common root-cause categories and diagnostic cues:

• Clerical errors — transcription mistakes, unit conversion errors, mislabelling and decimal point placement. These are not direct reflections of analytical competence but can indicate weaknesses in result reporting procedures or LIMS configuration.
• Technical problems — mistakes at any step of the analytical workflow: sample preparation, reagent quality, instrument setup, incubation conditions, analyst error or use of an outdated procedure. If investigations do not reveal an immediate cause, re-examine method validation and suitability for the matrices and ranges tested.
• PT scheme or material issues — inappropriate scheme selection, non-representative PT items, or problems with assigned values. Discuss anomalies with the PT provider and consider scheme selection guidance to ensure appropriateness.

Illustrative case summaries:

• Example (clinical tumor markers): A 20% deviation in PT was traced to an incorrect unit conversion applied in the LIMS after a software update; internal controls were unaffected and patient reports were in a different unit, so clinical results were not impacted. The solution involved correcting the unit conversion configuration and verifying report outputs.
• Example (food microbiology, Listeria): Underestimation was due to poor growth resulting from incorrect incubation time/temperature. A 5 Whys analysis revealed an out-of-date procedure had not been distributed because document-control workload prevented timely dissemination. Corrective actions included updating document-control processes and retraining.

Benefits and practical applications

A structured approach to PT failures provides several benefits:

• Faster identification of true technical faults versus administrative or scheme-related issues
• Reduced risk of reporting incorrect patient or customer results by checking for systemic impacts
• Targeted corrective actions that improve operational efficiency (e.g., LIMS settings, document control, training)
• Better dialogue with PT providers to resolve scheme or material problems
• Support for accreditation compliance through documented investigations and verification of corrective actions

Future trends and potential applications

Expected developments and opportunities include:

• Stronger integration between LIMS, instrument software and PT reporting to reduce clerical errors and ensure consistent units and metadata transfer
• Automated trend analysis and early-warning systems from IQC and historical PT data using analytics and machine learning to detect subtle performance shifts before PT rounds
• Increased emphasis on PT scheme selection tailored to laboratory scope and matrix/level matching, including more realistic commutable materials
• Improved digital records for document control and distribution to avoid outdated procedures reaching analysts
• Greater collaboration between PT providers and laboratories to investigate anomalous results and refine assigned values or materials

Conclusion

Every unsatisfactory PT result warrants investigation. A documented, stepwise root-cause analysis that considers clerical, technical and scheme-related origins will usually identify corrective actions. Laboratories should scale the depth of investigations to the analytical importance and recurrence of failures, verify effects on prior results, implement and record corrective measures, and confirm their effectiveness. Proactive measures—robust document control, reliable LIMS configuration, method validation and staff training—reduce the likelihood of recurrence and support accreditation and client confidence.

References

• Brookman B, Mann I (eds). Eurachem Guide: Selection, Use and Interpretation of Proficiency Testing (PT) Schemes. 3rd ed. 2021.