CSI - Forensic Serology 

Key Point: ^^serology^^ is a term used to describe a broad range of laboratory tests using reactions of blood serum and other bodily fluids

[[Nature of Blood[[

Blood → a highly complex mixture of cells, enzymes, proteins, and inorganic substances

Plasma → the fluid portion of blood, composed primarily of water

Red blood cells (erythrocytes), white blood cells (leukocytes), and platelets→ the solid materials suspended in plasma

Antigens (usually proteins) → located on the surface of red blood cells and are responsible for blood-type characteristics

[[Blood Typing[[

There are more than 15 types of blood antigen systems that have been identified, but the most important are the A-B-O and Rh systems

A-B-O System → If an individual has type A antigens, they are blood type A. If an individual has type B antigens, they are blood type B. If an individual has both type A and B antigens, they are blood type AB. If an individual has neither A nor B antigens, they are blood type O

Rh protein → A factor that determines if a person has a positive or negative blood type. If an individual has this protein, they are positive, and if they don’t have this protein, they are negative

[[Forensics of Blood[[

3 questions must be answered by the forensic investigator when suspected blood stains are found at a crime scene:

  1. Is it blood? (Answered with the benzidine test, kastle-meyer test, hermastix, and luminol test)
  2. Is it human blood? (Answered with the precipitin test)
  3. Can it be associated with an individual? (Answered with DNA profiling)

[[Testing for Blood[[

Kastyle-Meyer color test → A test that determines if a substance is blood. When met with the test, the hemoglobin in the blood shows up deep pink

Luminol test → A test designed to search out trace amounts of blood located at crime scenes. When met with the test, blood produces light (luminescence) in dark areas

Microcrystalline tests (like Takayama and Teichm) → Tests that depend on the addition of specific chemicals to the blood so that characteristic crystals will be formed

Precipitin test → A test that uses antisera to determine if a stain of blood is of human or animal origin

[[A-B-O vs DNA[[

A-B-O → A system used to characterize polymorphic blood enzymes and proteins. It sorts blood into groups A, B, O, and AB

DNA Analysis → A field that allows forensic scientists to associate blood and semen stains to a single individual

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