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Laboratory Orientation and Testing of Body Fluids and Tissues for Forensic Analysts

Screening Tests

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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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