Presumptive vs Confirmatory Testing
Definition
Presumptive tests (Phadebas) give rapid screening results but have cross-reactants; they justify further analysis. Confirmatory or highly specific tests (RSID-Saliva, mRNA analysis) provide stronger identification and are reported with greater confidence.
- Presumptive test example
- Phadebas (amylase)
- Confirmatory example
- RSID-Saliva, mRNA analysis
- Presumptive limitation
- Cross-reactants can trigger a positive
- Confirmatory strength
- Higher specificity for the body fluid claimed
Common questions
What can cause a false positive on the Phadebas amylase test?+
Amylase is also present in other body fluids and some plant and bacterial sources, so a positive Phadebas result does not by itself prove saliva. It flags the stain for a more specific follow-up test rather than closing the identification.
Why is RSID-Saliva considered stronger evidence than an amylase screen?+
RSID-Saliva targets a protein marker that is far more specific to saliva than amylase activity, so a positive result carries less risk of coming from an unrelated source and is reported with correspondingly greater confidence.
Related terms
- Alpha-Amylase (Salivary)
- An enzyme encoded by the AMY1 gene and secreted by the parotid, submandibular, and sublingual glands. It cleaves starch at alpha-1,4-glycosidic bonds...
- Double-Swab Technique
- A collection method for dried biological stains in which a moistened swab rehydrates and lifts the stain from the surface, followed immediately...
- Isoforms of Amylase
- The human genome encodes multiple AMY loci. AMY1 products are expressed in saliva; AMY2 products are expressed in the pancreas. The two...
- Phadebas Test
- A colorimetric presumptive test for alpha-amylase activity. Phadebas tablets contain a blue-dyed insoluble starch; amylase releases soluble blue dye that is measured...
- RSID-Saliva
- Rapid Stain Identification of Saliva. An immunochromatographic lateral-flow assay using monoclonal antibodies specific to human salivary amylase. More specific than Phadebas, with...