Quality Systems: ISO 17025 and Accreditation

ISO/IEC 17025:2017 (the current version) is structured around two sets of requirements: general requirements (covering impartiality and confidentiality), structural requirements (organisation and management), resource requirements (personnel, facilities, equipment, traceability of measurement), process requirements (method selection, validation, sampling, handling, records), and management system requirements (documentation, internal audit, management review). Each section contains specific prescriptive requirements that the accreditation assessor verifies.

For forensic laboratories, the 2017 revision introduced a more risk-based approach compared to its predecessor. Laboratories are expected to identify the risks that could affect the reliability of their results, from sample integrity risks to bias risks to equipment failure risks, and to have documented controls proportionate to those risks. This makes the standard compatible with the bias-management approaches discussed in the cognitive bias literature.

ISO 17025 is an international standard. Accreditation against it is conducted by national accreditation bodies (NABs), which are themselves assessed for competence by ILAC. The ILAC Mutual Recognition Arrangement (MRA) creates a framework in which a laboratory accredited by one MRA-signatory body is recognised as equivalent to a lab accredited by any other signatory body. This underpins international trade agreements (a drug test result from an accredited Indian lab is accepted in Australia without re-testing) and mutual legal assistance in criminal investigations.

• NABL (National Accreditation Board for Testing and Calibration Laboratories): India's primary testing and calibration laboratory accreditation body, ILAC MRA signatory, accredits CFSL and several State FSLs.
• ANAB (ANSI National Accreditation Board): operates in the United States; provides forensic-specific accreditation programmes including for DNA, toxicology, and trace evidence laboratories.
• UKAS (United Kingdom Accreditation Service): the sole national accreditation body in the UK; accreditation to 17025 is required by the Forensic Science Regulator's Codes of Practice for providers in the criminal justice system.
• NATA (National Association of Testing Authorities): Australia's accreditation body; operates a dedicated forensic science programme.
• DAkkS (Deutsche Akkreditierungsstelle): Germany's national body; accredits German forensic institutions.

Accreditation is not a once-only event. Initial accreditation involves a document review and an on-site assessment. Once granted, it is maintained through annual surveillance visits and a full re-assessment on a four or five year cycle. In between, the laboratory must submit proficiency testing results and report any significant changes, such as a change of method, a key personnel departure, or a serious non-conformity, to the accreditation body. Loss of accreditation is possible if corrective actions are not completed within agreed timescales.

Internal quality controls, such as blank samples, reference materials, and duplicate analyses, are necessary but not sufficient. They can confirm that an instrument is working and that the analyst is applying the protocol correctly, but they cannot confirm that the protocol itself is producing accurate results: the people designing the controls are the same people whose competence is under scrutiny. Proficiency testing by an external provider addresses this limitation.

In a proficiency test (PT), the scheme provider dispatches samples to participating laboratories. The laboratories analyse the samples using their normal operational methods, as they would for real casework, and report results. The scheme provider compares results against the known reference values and against each other, and generates a performance report showing whether each lab's results fall within acceptable limits (typically expressed as a z-score, where a score between minus two and plus two is satisfactory).

An unsatisfactory proficiency test result does not automatically trigger loss of accreditation. The accreditation standard requires the laboratory to investigate the cause, implement corrective action, and provide evidence that the corrective action worked. What matters is whether the lab has a functioning system for identifying and fixing problems, not whether every single PT result is perfect. Repeated unsatisfactory results in the same area, or failure to investigate root cause, are what trigger escalation.

Method validation is the systematic process of characterising an analytical method's performance. For a forensic method, this typically involves testing the method across a matrix of samples, concentrations, and interferants, measuring performance parameters, and documenting the results so that any laboratory using the method knows its capabilities and its limits.

• Specificity: does the method correctly identify the target analyte and not confuse it with similar compounds? A drug screening method that tests positive on cold medication is not specific enough for forensic use without confirmation.
• Sensitivity and limit of detection: what is the lowest concentration the method can reliably detect? Below the limit of detection, a result is reported as 'not detected', not as a zero value.
• Linearity: across what range of concentrations does the method produce results proportional to the true concentration? Outside the linear range, quantitative results are unreliable without correction.
• Accuracy and precision: accuracy is how close results are to the true value; precision is how repeatable results are across replicate analyses. A method can be precise but inaccurate (consistently biased) or accurate but imprecise (correct on average but variable).
• Robustness: how much do small changes in conditions (temperature, reagent lot, analyst) affect results? A method with high robustness holds its performance despite minor variation in laboratory conditions.

A forensic laboratory does not always need to re-validate a method from scratch if a validated method already exists in the scientific literature. In that case, the lab may perform method verification, a smaller exercise confirming that the method works as documented in their specific laboratory setting, with their specific equipment and personnel. The distinction between full validation and verification matters when a method is challenged in court.

Measurement uncertainty (MU) is not an admission that the result is wrong. It is a quantification of the fact that every measurement process has limits: instrument noise, calibration imprecision, sample preparation variability, and matrix effects all contribute. ISO 17025 requires laboratories to estimate uncertainty and to include it in reports for quantitative results.

The practical courtroom consequence is clearest in blood-alcohol cases. If the legal threshold is 80 mg/100 ml and the measured result is 85 mg/100 ml, the result appears to exceed the limit by five units. But if the method's measurement uncertainty is plus or minus six mg/100 ml, the true value could be as low as 79 mg/100 ml, just below the threshold. Courts in different jurisdictions handle this differently. Some apply a 'benefit of the doubt' approach and acquit if the uncertainty range straddles the threshold. Others treat the measured value as the reported result and leave uncertainty for the expert to explain in testimony.

The legal relevance of accreditation varies by jurisdiction and by court, but the direction of travel is consistent: more jurisdictions are making accreditation a formal requirement rather than a desirable attribute of forensic evidence.

In England and Wales, the Forensic Science Regulator Act 2021 placed the regulator's Codes of Practice on a statutory basis. Providers of forensic science to the criminal justice system are required to meet the Codes' quality standards, which include ISO 17025 accreditation as a core requirement. Results from non-compliant providers can be challenged on admissibility grounds. The Act created an enforcement mechanism that the previous non-statutory regulatory framework lacked.

In the United States, the DNA Identification Act of 1994 and subsequent amendments require all public DNA labs to meet FBI quality assurance standards and undergo external audits, with accreditation (typically through ANAB, the ANSI National Accreditation Board, formerly the accreditation arm known as ASCLD/LAB before its 2016 merger into ANAB) as the mechanism. For non-DNA forensic disciplines, accreditation requirements are less uniform across states, though OSAC (Organization of Scientific Area Committees) produces standards that increasing numbers of jurisdictions reference in their admissibility analysis.

In India, NABL accreditation of state and central FSLs has been expanding, and results from accredited laboratories carry more weight in court proceedings. Courts have in some cases questioned the reliability of results from non-accredited laboratories or those without documented QA procedures, though there is no general statutory admissibility requirement linked to accreditation comparable to the UK regime.