Quality Assurance in DNA Testing

Quality Assurance in DNA Testing - Setting Gold Standards

• Quality Assurance (QA): Proactive, process-oriented system to prevent errors.
• Quality Control (QC): Reactive, product-oriented measures to detect errors.
• Validation: Confirming a method is fit for its intended purpose.
  • Internal (lab-specific) & Developmental (new methods).
• Accreditation: Formal recognition of competence by an authoritative body (e.g., NABL).
• Standards: ISO/IEC 17025:2017 (general requirements for testing/calibration labs), ISO 15189:2022 (medical laboratories), NABL guidelines.

⭐ Proficiency Testing: External quality assessment where labs analyze blind samples; crucial for maintaining accreditation and ensuring inter-laboratory comparability. Essential for NABL accreditation in India.

• Key Elements: SOPs, staff training, equipment calibration, reagent control, audit trails, corrective actions (CAPA).

Quality Assurance in DNA Testing - Guarding the Source

• Goal: Ensure DNA integrity & reliability; prevent contamination & degradation.
• Critical Pre-Analytical Steps:
  • Collection: Sterile tools, proper technique. Avoid cross-contamination (PPE, separate handling).
  • Labeling: Accurate, complete, unique ID. Date, time, collector, source.
  • Packaging: Air-dry biological stains. Use breathable paper containers. Tamper-evident seals.
  • Transport & Storage: Prompt, secure. Maintain temperature (e.g., blood 4°C, tissue -20°C).
• Chain of Custody (CoC): Unbroken, chronological documentation of evidence handling.

![Tamper-evident forensic evidence bags](https://ylbwdadhbcjolwylidja.supabase.co/storage/v1/object/public/notes/L1/Forensic_Medicine_DNA_Profiling_and_Forensic_Biology_Quality_Assurance_in_DNA_Testing/e3119059-6b5a-43c0-b46f-f28824212a09.jpg)

⭐ Any lapse in the Chain of Custody (CoC) can critically undermine the legal admissibility of DNA evidence.

Quality Assurance in DNA Testing - Lab Bench Vigilance

• Goal: Ensure reliable, error-free, reproducible DNA results.
• Key Areas & Controls:
  • Sample Integrity: Strict chain of custody; separate pre & post-PCR zones to prevent carryover contamination.
  • DNA Extraction: Use validated methods; monitor yield & purity (e.g., A260/A280 ratio).
  • Quantification: Accurate DNA assessment (e.g., qPCR) for optimal PCR input (typically 0.5-2.0 ng).
  • PCR Amplification:
    • Positive Control: Known DNA; verifies reagents, thermal cycler, and overall process efficacy.
    • Negative Control (Reagent Blank): Contains all reagents except DNA; detects reagent or environmental contamination.
    • Internal PCR Control (IPC): Co-amplified non-target DNA sequence; monitors for PCR inhibitors in the sample.
    • Allelic Ladder: Mixture of all common alleles for each STR locus; essential for accurate allele designation and sizing calibration.
  • Electrophoresis (e.g., Capillary Electrophoresis): Validated run modules; regular calibration with size standards.
• Systemic QA:
  • Regular instrument calibration & preventative maintenance.
  • Validation of methods, instruments, and software before casework.
  • Proficiency testing (internal and external blind trials).
  • Adherence to Standard Operating Procedures (SOPs) & comprehensive documentation.

⭐ The inclusion of an allelic ladder in every STR analysis run is mandatory for accurate genotyping, as it provides a reference for allele calling by sizing the DNA fragments.

Quality Assurance in DNA Testing - Upholding Standards

• Core Components:
  • SOPs: Standardized protocols.
  • Validation: Methods, instruments, software.
  • Controls: Batch-wise positive, negative, allelic ladders.
  • Interpretation Guidelines: Thresholds (analytical, stochastic), mixtures.
  • Documentation: Comprehensive (CoC, batch records, training).
• Verification & Improvement:
  • Proficiency Testing (PT): Regular internal/external competency checks.
  • Audits: Periodic internal/external system reviews.
  • Peer Review: Independent check of reports/interpretations.
  • CAPA: Addressing non-conformities, preventing recurrence.
  • Accreditation: To FBI QAS (effective July 1, 2025) and ISO/IEC 17025 (e.g., NABL).

⭐ Stochastic threshold is vital for interpreting low-template DNA (LCN) and mixed samples accurately.

High‑Yield Points - ⚡ Biggest Takeaways

• NABL accreditation is crucial for DNA laboratory credibility.
• Adherence to validated Standard Operating Procedures (SOPs) is mandatory.
• Proficiency testing (internal/external) ensures analyst and lab competence.
• Rigorous chain of custody documentation is vital for evidence admissibility.
• Validation of methods, equipment, and software is a prerequisite.
• Essential Quality Control (QC) includes blanks, controls, and replicates.
• Regular audits (internal/external) ensure ongoing compliance and quality.