Phadebas Test
Definition
A colorimetric presumptive test for alpha-amylase activity. Phadebas tablets contain a blue-dyed insoluble starch; amylase releases soluble blue dye that is measured visually or spectrophotometrically. Detects all amylase isoforms.
- Target analyte
- Alpha-amylase enzyme
- Principle
- Blue-dyed starch tablet, dye released by amylase
- Reading method
- Visual colour change or spectrophotometric
- Specificity
- Detects all amylase isoforms, not saliva-specific
Common questions
Can the Phadebas test give a false positive from a non-saliva source?+
Yes. Amylase is also present in other body fluids and some environmental sources, so a positive Phadebas result is treated as presumptive evidence of saliva rather than confirmation, and is typically followed by a saliva-specific test.
What confirmatory test is used after a positive Phadebas result?+
Labs commonly follow up with RSID-Saliva, an immunochromatographic test targeting a salivary-specific marker, to confirm that the amylase activity detected actually originates from saliva.
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
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- 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...
- Presumptive vs Confirmatory Testing
- Presumptive tests (Phadebas) give rapid screening results but have cross-reactants; they justify further analysis. Confirmatory or highly specific tests (RSID-Saliva, mRNA analysis)...
- 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...