Archived | Laboratory Orientation and Testing of Body Fluids and Tissues for Forensic Analysts | Screening Tests

Screening Tests
Test	Indicator	Sensitivity	Comment
Benzidine	Blue color	++++	Carcinogen
Tetra methyl benzidine	Blue color	+++	Probable carcinogen
o-Tolidine	Dark green	+++	Probable carcinogen
Phenolphthalein or Kastle Meyer test	Pink color	++	Relatively safe
Leucomalachite green	Green color	++	Relatively safe
Luminol (5-amino-2,3-dihydro-1,4 phthalazinedione)	Fluorescence	+++++	Probable carcinogen
Note: The product "Hemastix", manufactured by Bayer and widely used in clinical screening tests for detection of blood in urine, provides a safe and simple alternative to the above reagents. It contains o-Tolidine immobilized behind a membrane. The membrane acts as a barrier to contact by the user, but permits aqueous extracts to pass and react with the reagent.

These tests are not specific for blood. Other biological materials, such as fruits, possess peroxidase activity, and oxidizing agents may be present on surfaces. Some laboratories have used two or more of the tests listed in the table and reported the second as confirming the first. However, since they are all presumptive tests, carrying out two or more tests does not substitute for or constitute a confirmatory test.

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Date Created: June 28, 2023