Hundreds of blood tests are performed every day in today’s modern labs. In general, there are four main types of blood tests:

• Hematology tests
• Biochemistry tests
• Microbiology tests
• Serology tests

Hematology tests examine the blood to identify:

• The types and numbers of blood cells that are present (e.g., red blood cells, white blood cells and platelets)
  
  
• The appearance of the cells, especially their maturity
  
  
• The ability for the blood to form a blood clot and the speed at which clotting occurs

Biochemistry tests measure the levels of normally occurring chemicals and biochemicals in the blood, both individually and in relation to other chemicals. These measurements are compared to normal ranges and are used to determine whether blood biochemicals are in a proper and healthy balance. Biochemicals and other substances that may be studied include:

• Sodium
• Cholesterol and other fats
• Vitamins and minerals
• Hormones
• Blood gases
• Prescription drugs
• Recreational drugs
• Alcohol

Not only can biochemical tests precisely measure these substances, but they can also be used to indicate how well some organs and organ systems are functioning. For instance, the amount of blood sugar (glucose) in the bloodstream can help diagnose or monitor diabetes, and indirectly reflect how much insulin is being produced by the pancreas.

Microbiology tests examine blood for the presence of infectious microscopic organisms such as:

• Bacteria
• Fungi
• Viruses (in most clinical labs a serology test is used)
• Parasites

Microbiology tests include:

• Smears, in which a small amount of blood is placed on a glass slide for examination under a microscope. Sometimes the blood smear is stained with special dyes before examination.
  
  
• Blood cultures, in which a small amount of blood is placed in a nutrient broth, incubated for days or weeks and then examined for growth of disease-causing bacteria.

Serology tests (tests done on blood serum) can detect the presence of antibodies that are produced by white blood cells. They are frequently used to detect viral diseases. Most hospital laboratories do not have the equipment or specially trained personnel necessary to isolate the viruses themselves, so serology tests are done instead to identify the infecting organism by studying the antibodies produced against it.