Blood Composition and Evidence Testing
Ever wonder what makes blood so useful for solving crimes? Human blood contains several key components that forensic scientists analyze. Erythrocytes (red blood cells) transport oxygen and contain hemoglobin, which gives blood its red color. Leukocytes (white blood cells) fight infection and are part of the immune system. Thrombocytes (platelets) help with blood clotting, and plasma carries nutrients, hormones, and waste products.
When investigators find potential blood at a crime scene, they first perform presumptive testing. Tests like Kastle-Meyer (using phenolphthalein) react with hemoglobin to suggest if a sample is blood. This is followed by confirmatory testing to verify it's actually blood by examining other properties like antigens.
Blood typing uses the ABO system to classify blood into four types (A, B, AB, and O) based on the antigens present on red blood cells. Each blood type also has specific antibodies—proteins that interact with antigens. When antibodies encounter the wrong type of antigen, they cause agglutination (clumping), which is how blood typing tests work.
Fascinating Fact: Red blood cells only live for about 120 days before being recycled by your liver and spleen. Your body constantly produces new ones to replace them!
Blood evidence can narrow down suspects by matching blood types, though common types like type A (found in 42% of the population) may not be conclusive on their own. In a crime scene investigation, blood evidence must be considered alongside other evidence like fingerprints, hair samples, and potential motives.
