Destructive Testing
Definition
Any test that consumes, extracts, or chemically alters the stain material: cutting a fabric swatch, swabbing a surface, adding a chemical reagent. Once performed, the consumed portion cannot be re-examined.
- Field
- DNA and biological evidence handling
- Examples
- Fabric cutting, surface swabbing, reagent application
- Consequence
- Consumed portion cannot be re-examined
- Planning principle
- Non-destructive methods and documentation come first
Common questions
Why does test order matter so much for destructive testing on a stain?+
Once a swab or cutting is taken and consumed, no other analyst can re-test that exact portion, so labs sequence non-destructive steps like photography, presumptive screening and visualisation first, and reserve the smallest sufficient sample for destructive DNA extraction to preserve material for a defence retest.
What can be done if only a small stain is available and a retest is disputed?+
Analysts document the stain thoroughly before consuming it, sometimes split a limited sample so a portion is reserved, and record extraction volumes and methods precisely, so the process itself, not just the leftover material, can be scrutinised if the result is challenged.
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...
- 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...
- Sequential Testing Protocol
- The standardised order in which biological stains are examined: presumptive test, then confirmatory test, then species confirmation, then typing and DNA analysis....