Quality Assurance in Serology Laboratories

ISO/IEC 17025 has two main parts: management requirements and technical requirements. The management requirements address the quality system itself, including document control, complaint handling, audits, and corrective action. The technical requirements address what the laboratory actually does: method selection and validation, equipment qualification, sampling and sample handling, and result reporting.

For serology, the most critical technical requirements are method validation and measurement uncertainty. Method validation means demonstrating, with data, that a test does what it is claimed to do: that luminol detects blood at the relevant concentrations, that the anti-human antibody in a species test does not react with the species it is likely to encounter as an interferent, and that the DNA extraction step recovers sufficient material from the substrate types encountered in casework. These are not one-time demonstrations; they must be performed when a method is first adopted, when a reagent lot changes, and when any significant change is made to the protocol.

In England and Wales, the Forensic Science Regulator issues Codes of Practice that set quality requirements for forensic providers, and these reference ISO 17025 as the baseline. In the United States, OSAC produces approved standards that are not mandatory federally but are adopted by many state and local laboratories. ENFSI, covering European forensic institutes, issues guidelines and coordinates interlaboratory comparisons. The specifics differ by jurisdiction, but the underlying framework is consistently ISO 17025.

Serology relies on biological and chemical reagents whose activity changes over time. Anti-human serum antibodies, peroxidase substrates, and ABO antisera all have defined storage conditions and expiry dates. The moment a new batch of reagent arrives, it should undergo lot-acceptance testing: running the new lot against samples of known composition alongside the current in-use lot to confirm that performance is equivalent.

• Expiry date monitoring: reagents past their expiry must not be used for casework. A register of expiry dates with flagged alerts prevents inadvertent use.
• Cold-chain documentation: temperature-sensitive reagents require refrigerator or freezer storage with temperature logging. Breaks in the cold chain may invalidate a lot even before expiry.
• Lot-acceptance testing: new lots are tested against known positive and negative samples before being introduced to casework. Results are documented and retained.
• In-use stability: some reagents, such as reconstituted antibodies, have a shorter in-use period than the unopened shelf life. The opened date and in-use expiry are tracked separately.

A reagent failure uncovered in retrospect, after casework results have been reported, is a significant quality event. The laboratory must assess whether all results produced while the compromised reagent was in use are affected, and may need to re-test samples if they are still available.

Controls are the mechanism by which an analyst confirms that the test system worked on the day the casework was run. A positive control is a sample that should give a positive result. If it does not, something is wrong with the system: the reagent may have degraded, the equipment may have malfunctioned, or the analyst may have made an error. A negative control is a blank, either distilled water or a substrate known to contain no blood, that should give no signal. If it does signal, there is contamination in the reagents or the test environment.

The practice of bracketing casework samples with controls applies to every stage where an error could invalidate results: the presumptive test, the confirmatory test, the species identification, and the DNA extraction and amplification. A DNA run with a failed positive amplification control means the PCR conditions were not optimal; results from that run cannot be reported as valid.

Internal controls confirm that a test run was technically valid. Proficiency tests confirm that the laboratory produces correct results on samples of known composition when the analyst has no prior knowledge of those results. An analyst may unconsciously apply different interpretive standards to a sample known to be positive than to one that is not; blind proficiency testing removes that bias.

Proficiency testing providers for forensic serology include Collaborative Testing Services (CTS) in the United States and GFSA (Groupe Forensique SA) in Europe, among others. When a laboratory fails a proficiency test, the failure triggers a corrective-action investigation, a root-cause analysis, and remedial training or method revision before casework continues. A history of proficiency test results is part of the quality record that may be disclosed in legal proceedings.

Serology laboratories handle biological material, and the main contamination risk in a pre-DNA context is cross-transfer of bloodstains between samples. In a DNA-typing context, the contamination risk expands to include analyst DNA, which is both extremely sensitive and, if an analyst's profile is not in the exclusion database, potentially interpretable as evidence.

• Physical zoning: pre-PCR and post-PCR areas must be physically separated; amplified product is a contamination source that can produce false positives in pre-amplification areas.
• Personal protective equipment: gloves, masks, and gowns protect samples from analyst DNA and protect analysts from biohazardous material. Gloves are changed between samples.
• Elimination database: all laboratory staff and investigators who access scenes are profiled and their DNA profiles registered so that any contamination can be recognised as such.
• Single-use consumables: pipette tips, tubes, and swabs are not reused. Cutting tools are cleaned and decontaminated between samples.

Crime scene contamination is a separate but related concern. Scene-attending personnel whose DNA could be deposited before collection arrive must be identified, and their elimination profiles must be available to the laboratory. This is particularly relevant in cases involving small-scale touch-DNA evidence on contact surfaces.

In England and Wales, the Forensic Science Regulator Act 2021 gave the Regulator statutory powers to set and enforce quality standards, requiring all forensic science providers operating in the criminal justice system to hold accreditation to ISO 17025 or equivalent for each forensic activity they perform. This is among the most formal mandatory frameworks globally.

In the United States, there is no single federal mandate, but the Paul Coverdell Forensic Science Improvement Act provides funding incentives tied to accreditation, and most state crime laboratories now hold ASCLD/LAB-International or ANAB accreditation, both of which are ISO 17025-based. The PCAST report of 2016 reinforced calls for mandatory accreditation and proficiency testing for all forensic disciplines.

In Australia, NATA (National Association of Testing Authorities) accredits forensic laboratories under its ISO 17025-aligned program. In India, the NABL (National Accreditation Board for Testing and Calibration Laboratories) provides ISO 17025 accreditation, with several Central Forensic Science Laboratory units and state forensic labs accredited. Coverage across the country remains uneven at the district and state level.