The Forensic Scientists in the Biology section collect trace evidence and utilize serology screening tests to detect and then identify stains during the examination of physical evidence. Serology is the detection and identification of bodily fluids. Most often, the stain of interest for detection and identification is blood. Homicides, assaults and burglaries are some of the more common cases in which this type of screening may be necessary. The scientists perform both presumptive and confirmatory tests for blood. A presumptive or indicative test is one that establishes the possibility that a specific body fluid may be present. A confirmatory test provides a more specific identification of a bodily fluid.

The laboratory no longer accepts sexual assault evidence. Sexual assault kits and related evidence should be submitted to the Department of Public Safety laboratory in Houston.

Blood

Presumptive Testing

Phenolphthalein

For blood, the presumptive test used in the Biology section is the phenolphthalein or Kastle-Meyer test. This test produces an immediate bright pink color in the presence of blood due to a peroxidase reaction catalyzed by hemoglobin present in the blood.

Confirmatory Testing

ABAcard® HemaTrace®

ABAcard® HemaTrace® is the confirmatory test used for blood. This test works by using antibodies to human hemoglobin to allow detection of blood. Although the ABAcard® HemaTrace® test is confirmatory for the presence of blood, it is considered indicative for the presence of human blood. This is because there are certain animals (i.e. higher primates, etc.) that may also give a positive reaction with this test.

Alternate Light Source

The Biology section also uses alternate light sources for screening. This specialized lighting can reveal stains of bodily fluids that may not be visible to the unaided eye. Some bodily fluids like blood, semen and saliva may be detected under these specialized lighting conditions making them easier to locate on clothing or other evidence.

DNA/Trace

Samples that require DNA, hair and fiber, or paint analysis will be forwarded to an accredited laboratory with those capabilities. Evidence is usually forwarded to the Texas Department of Public Safety Laboratory system, unless other arrangements are made with the submitting agency or prosecuting official.