Blood Tests

Blood tests are among the most comprehensive -- and complex -- laboratory tests used to monitor the health of people living with HIV. Very often, healthcare providers will ask for blood to be taken every three to six months, or sometimes more frequently, depending on the patient's health or if he or she is enrolled in a clinical trial.

Blood samples are typically used to perform five different types of tests:

• Hematology Tests: Used to measure the number and amount of "formed elements" in the blood. Formed elements include red blood cells, white blood cells, and platelets.

• Blood Chemistry Tests: Used to measure chemicals in the blood, such as those produced by the liver, as well as nutritional elements such as vitamins, proteins, fats, and sugar.

• Microbiology Tests: Used to find certain disease-causing microorganisms in the blood. These can include bacteria, fungi, and parasites.

• Serology Tests: Used to find antibodies produced by the immune system in response to specific disease-causing microorganisms. The HIV and hepatitis C virus (HCV) antibody tests are examples of serology tests.

• HIV-Specific Tests: Viral load, a measurement of the amount of HIV in a milliliter of blood, is an example of an HIV-specific blood test.

Before going into a more detailed overview of the various blood tests, it's important to understand how the tests are reported. The report sent to your healthcare provider by the laboratory lists the results of your blood tests. It contains a lot of information but is fairly simple to understand. Listed on your lab report are the names of the tests performed, the results of the tests, and the normal reference ranges. Your results are typically reported either as an absolute number per specified unit or as a percentage. These results can then be compared with the reference ranges, which reflect average results found in a healthy population.

It's important to understand, however, that a test result outside a given reference range doesn't necessarily mean that you are sick or having a problem. For starters, different labs use different reference ranges. Blood test results can mean many different things and are often analyzed by healthcare providers in the context of other important factors, such as symptoms (fever, pain, or diarrhea, for instance) and the results of a physical examination. Moreover, certain blood test results can vary greatly depending on the time of day blood is taken, whether or not you've eaten before having blood drawn, if you've recently received an immunization, or if you're experiencing another illness -- for example, the flu or a herpes outbreak -- at the time blood is taken. Also, there is always the chance that the lab result is an error. If you have questions about any of your blood tests, be sure to speak with your healthcare provider.