Here the answers become less precise. Blood is mostly water, but it also contains a number of additional materials including cells, proteins, and enzymes. The fluid portion, or plasma, is mostly water. The serum is yellowish and contains platelets and white blood cells. Clotting and crystallization indicate age. Because blood quickly clots when exposed to air, serologists must separate the serum from the clotted material. The serum contains antibodies that have forensic applications, and red blood cells have substances such as antigens on their surfaces that also have forensic applications. Testing for testosterone levels and chromosome testing can determine sex. And certain controversial, racial genetic markers based on protein and enzyme tests may indicate race. Other body fluids may contain the same antibodies and antigens found in blood. Therefore, similar tests work on these fluids as well.
