Forensic Serology is a unit within the Central Regional Laboratory. Approximately 3,000 cases are submitted yearly to the Forensic Serology unit to be searched for biological evidence containing potential DNA. The majority of these cases are sexual assaults, burglaries, homicides, assaults, and robberies. The types of items submitted in these cases are varied and include sexual assault evidence collection kits, condoms, articles of clothing, bed linens, weapons, masks, swabs collected at the scene, and any item which may contain biological stains with potential DNA.
For evidence submittal to the Forensic Serology Unit, see the Evidence Field Manual link on the OFS home page.
The Forensic Serology Section is primarily responsible for the detection and identification of biological material (i.e., blood, semen, saliva, and urine) on physical evidence in order to:
Analysts in the Forensic Serology Unit document the physical evidence, screen the evidence for the presence of biological materials, and collect and preserve biological samples for further analysis. Based on the case information provided and established casework management protocols, scientists select an appropriate evidence processing scheme which may involve chemical, enzymatic, immunological, and/or microscopic techniques.
The first step in a serological examination is the documentation and visual examination of evidence. Biological stains may, or may not, be visible to the unaided eye. The alternate light source (ALS) allows the scientist to visualize biological stains invisible to the naked eye. Performed in a darkened room while wearing colored goggles, stains will fluoresce when viewed at different wavelengths of visible light. Questioned stains are then subjected to the appropriate presumptive and confirmatory tests, as described below.
Presumptive test for semen
The Acid Phosphatase (AP) Test is a presumptive test for semen. Acid phosphatase is an enzyme that is present in high concentrations in seminal material. If a purple color change occurs within a minute, the test is considered positive for the possible presence of semen. This is not a conclusive test as AP is also found in other substances (e.g., vaginal secretions, douches, and contraceptive creams), although at lower concentrations.
Using compound microscopes, scientists search for spermatozoa, or sperm cells, on slides prepared from swabs, clothing, etc. The slides are stained using the Kernechtrot-Picroindigocarmine Stain, or “Christmas Tree Stain”, in which the heads of the spermatozoa are colored red and the tails are colored green.
If spermatozoa are not detected, an extract of the stain is tested for p30, a protein synthesized in the prostate gland. An immunoassay is used to test for p30.
Presumptive tests for blood
The Kastle-Meyer (KM) Test is a presumptive test for blood. Three reagents (ethanol, KM reagent, and hydrogen peroxide) are applied, in turn, to the suspected bloodstain. If blood is present, a pink color change will occur within seconds. This is not a conclusive test for blood as other materials could give a false positive result.
Luminol is a chemical that can be sprayed over a large area where even a small amount of blood may be present. Luminol reacts in the presence of hemoglobin and emits blue luminescence. The test is so sensitive it can detect minute traces of blood even after an attempt has been made to wash the blood away. This is not a conclusive test for blood as other materials could give a false positive result. Primarily, this test is conducted at the crime scene.
The Phadebas® Amylase Test is a presumptive test used to detect the presence of a-amylase, an enzyme present in high concentrations in human saliva. If amylase is present, a blue dye is released into solution. Alpha-amylase activity can be measured using a Ultraviolet-Visible spectrophotometer or, alternatively, visualized on reagent-coated paper.
Evidence found at the scene can be submitted for the collection of epithelial (i.e., skin) cells to determine who had extended exposure to the item. Areas of the item that have a high probability of accumulating epithelial cells, such as a shirt collar or the sweatband of a baseball cap, are swabbed in order to concentrate the epithelial cells to be submitted for DNA analysis.
The Forensic Serology Unit works hand-in-hand with other units when further analysis is required. Biological stains are sent to the DNA Laboratory for analysis. Hairs and fibers are sent to the Trace Evidence Unit for comparison. Also, items are submitted to the Crime Scene Investigation Unit for latent print analysis.
Crime Scene Assistance:
Scientists assist crime scene investigators by bringing the capabilities of the modern forensic laboratory to the field.
Scientists provide educational talks to various agencies and school groups.