Doctors do blood tests to check the CD4 panel and Viral load. CD4 panel counts the special type of White Blood cell that HIV kills. Viral load counts the number of HIV viruses in the blood. The doctor uses these tests in all HIV infected persons to find out when treatment is necessary, to see if treatment is effective or if a change in medication is needed. The doctor may use blood tests to check if HIV is affecting other parts of the body, check for other Sexually Transmitted Infections or to check on the Side Effects of medications. Ask your Health Care Provider about any blood tests and their results.