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Screening Tests
Home > Forensic Biology > Testing of Body Fluids & Tissues > Blood > Screening Tests
Most screening tests for blood depend on the peroxidase activity of hemoglobin. The most common tests depend on the oxidation of colorless reduced indicators, many of which are conjugated systems and are known or suspected carcinogens.
Screening Tests |
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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. |
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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.
Click here to watch a video about screening tests for blood.
