Confirmatory tests for detection of blood

As discussed in the previous lesson, microcrystalline tests such as the Takayama test and the Teichmann test, are used to confirm the presence of blood.

When certain reagents are added to the suspected area, crystals appear in case of blood stains which can be observed through the microscope. Although these tests are considered as confirmatory tests, it is important to note that they have limitations and certain crime laboratories in the USA have removed them from their standard procedures.

In case of the Teichmann test, studies have shown that rust and exposure interfere with the test results. Whereas for Takayama test, false negative results have been observed in case of aged blood stains. False negative refers to results not indicating the presence of blood when blood is actually present. Both these tests do not provide any information on the species origin of the blood and are tedious processes. These tests are temperature dependent and if the reagents are not properly heated, false negative results can be observed.

Given the limitations of these tests, there has been a gradual decline in their use across jurisdictions. Immunological tests, available as commercial kits like RSID and HemaTrace, provide more accurate and quicker results, and are now preferred as confirmatory tests for blood.