Proficiency Testing (PT)
Definition
A quality assurance mechanism in which laboratories analyse blind samples distributed by an external scheme coordinator and have their results compared against consensus or known-reference values. For F/A/E laboratories, CTS fire debris PT, ENFSI EWG PT, and CTS explosives PT are the principal schemes.
- Regulatory requirement
- ISO 17025 Clause 7.7.2 mandates regular PT participation. In India, NABL FORC 03 extends this to accredited forensic labs.
- Common PT schemes
- Fire and Explosives labs typically use CTS fire debris PT, ENFSI EWG PT, and CTS explosives PT schemes.
- Performance trigger
- A z-score greater than 2 (in absolute value) prompts mandatory corrective action by the laboratory.
Common questions
What's the difference between proficiency testing and method validation?+
Validation is a one-time check that a method works. Proficiency testing is ongoing. A lab validates its fire debris method once, then enters PT schemes regularly to prove it stays competent and the method stays in control. ISO 17025 requires regular PT participation as a quality checkpoint.
How do labs know if their PT results are good or bad?+
Results get scored as a z-score. A z-score below 2 (in absolute value) is satisfactory. Scores between 2 and 3 are questionable and warrant attention. Scores above 3 are unsatisfactory and trigger mandatory corrective action.
Who runs proficiency testing schemes and what do they do?+
Third-party coordinators like CTS, ENFSI, and OPCW send blind (unlabeled) samples to participating labs. Each lab analyzes the sample without knowing the correct answer. The coordinator then compares all results against the consensus value or a known reference and reports each lab's performance back as a z-score.
Related terms
- ISO/IEC 17025:2017
- The international standard specifying general requirements for the competence of testing and calibration laboratories. Covers management (document control, non-conforming work, audits) and...
- Method Validation
- The process of demonstrating that an analytical method does what it claims: that it correctly identifies the target analyte, at what sensitivity,...
- NABL
- National Accreditation Board for Testing and Calibration Laboratories, a constituent board of the Quality Council of India. It is the sole accrediting...
- Accreditation
- Formal recognition by a standards body (such as UKAS in the UK, A2LA in the US, or NABL in India) that a...
- Accuracy and Precision
- Accuracy is closeness to the true value, measured as recovery from a spiked CRM with the 80 to 120 percent window. Precision...
- ANAB
- The American National Standards Institute National Accreditation Board, formed after the merger of ASCLD-LAB with ANSI-ASQ National Accreditation Board in 2016. Now...
- ASCLD-LAB
- American Society of Crime Laboratory Directors Laboratory Accreditation Board; the legacy US forensic accreditation body before its merger into ANAB in 2016....
- Calibration
- A steganalysis technique that estimates the cover image statistics by cropping or decompressing and re-compressing the test image to produce a reference....
- Control Chart
- Time-series plot of a QC measurement with warning limits at ±2σ and action limits at ±3σ from validation data. Patterns such as...
- Corrective Action and CAPA
- The ISO 17025 Clause 8.7 requirement for root-cause analysis and documented corrective and preventive action (CAPA) following any nonconformity (PT failure, IQC...
- CTS (Collaborative Testing Services)
- A Herndon, Virginia-based proficiency testing provider offering fire debris analysis and explosives proficiency schemes. CTS distributes evidence-can samples containing burned substrate with...
- ENFSI DNA WG
- ENFSI DNA Working Group; the European body that publishes the DNA Profiling Best Practice Manual, the Evaluative Reporting Guideline, and coordinates the...
Explained in these topics
- ISO 17025, NABL, ENFSI and Quality Systems for Forensic Chemistry LaboratoriesExternal quality evaluation in which a laboratory analyses blind samples from a PT provider (CTS, ENFSI, OPCW) and receives z-score performance feedback. Requi...
- ISO/IEC 17025, SWGDAM, ENFSI and NABL AccreditationA scheme in which a third party sends blind samples to a laboratory and evaluates whether the laboratory's results match the consensus answer. Distinguished fr...
- Method Validation, Measurement Uncertainty and Proficiency TestingInter-laboratory comparison scored as a z-score: |z| below 2 satisfactory, 2 to 3 questionable, above 3 unsatisfactory. ISO 17025 clause 7.7.2 requires regular...
- Quality Control Management in Forensic InstitutionsExternal inter-laboratory comparison where participating labs analyse the same blind sample and their results are compared against an assigned value. NABL FORC...
- Quality Systems: ISO 17025, NABL, ANAB, UKAS and Proficiency TestingA quality assurance mechanism in which laboratories analyse blind samples distributed by an external scheme coordinator and have their results compared against...