Sequential Testing Protocol
Definition
The standardised order in which biological stains are examined: presumptive test, then confirmatory test, then species confirmation, then typing and DNA analysis. Designed to answer each question using the minimum sample and the least destructive method before proceeding to the next stage.
- Order
- Presumptive, confirmatory, species, then typing/DNA
- Governing principle
- Minimum sample, least destructive method first
- Applies to
- Biological stains (blood, semen, saliva)
- Purpose
- Preserve material for later, more definitive tests
Common questions
Why not run DNA analysis first?+
DNA typing consumes and can destroy the limited stain material. Running presumptive and confirmatory tests first answers the basic identity questions cheaply, leaving enough sample for DNA only when it is actually needed.
What happens if a presumptive test is skipped?+
Skipping straight to confirmatory or DNA testing wastes scarce sample on questions a quick screening test could have answered, and can leave nothing for species confirmation or typing if the stain is small.
Related terms
- Chain of Custody
- The documented chronological record of who collected, handled, transferred, and examined a piece of evidence. For digital evidence, chain of custody includes...
- Destructive Testing
- Any test that consumes, extracts, or chemically alters the stain material: cutting a fabric swatch, swabbing a surface, adding a chemical reagent....
- Differential Extraction
- A two-step DNA extraction procedure used when a stain contains both sperm cells and non-sperm epithelial cells. The first step lyses epithelial...
- Non-Destructive Examination
- Any examination that does not consume or significantly alter the stain: visual inspection, alternate light source (ALS) examination, photography, and microscopy of...
- PCR Inhibitor
- A co-extracted substance that interferes with Taq polymerase activity or primer annealing. Common inhibitors in forensic samples include haemoglobin (from blood on...