Alpha-Amylase
Definition
Salivary enzyme. Detected by starch-iodine (clear zone in blue background) or the Phadebas reagent (blue colour from dye-linked starch). Concentration in saliva is 700 to 2000 times serum levels.
- Body fluid source
- Saliva
- Presumptive tests
- Starch-iodine, Phadebas
- Relative concentration
- 700 to 2000 times serum level
- Test category
- Presumptive, not confirmatory
Common questions
Is a positive amylase test proof that a stain is saliva?+
No, amylase also occurs at lower levels in other fluids and some environmental sources, so a positive starch-iodine or Phadebas result is only presumptive. A confirmatory step, such as an immunological test for the salivary isoform, is needed before saliva can be reported with confidence.
Why is the Phadebas test often preferred over starch-iodine in casework?+
Phadebas produces a clear blue color change that is easier to document and photograph on varied backgrounds and fabric colors than the starch-iodine clear-zone reaction, and it is more readily adapted to swab-based screening of large scene items.
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