Two tests are used to monitor immune health:

CD4Count test: This test monitors the number of CD4 (or Helper T) cells in a blood sample. This is expressed as a number of CD4 cells per cubic millimeter. A single CD4 count test does little to determine one’s general state of health. However, comparisons over time provide a better sense of immune health by providing data by which to determine whether CD4 count is stable or declining. Three tests, given three to six months apart, will be sufficient to determine a trend.

HIV Viral Load Test: This test measures the amount of HIV genetic material (RNA or DNA) in the blood. Viral load is often expressed as number of copies per milliliter (mL). Two types of viral load test are currently available, and they measure viral load in different ways. One test, called the branched-chain DNA (bDNA) test, measures viral load by causing the viral RNA in a sample to emit (give out) light; more light means that more virus is present in the patient's blood. The other test, called the reverse transcriptase polymerase chain reaction or RT-PCR test (commonly called PCR), chemically multiplies the amount of viral RNA in a blood sample, which makes it easier to estimate the amount of virus in the body. A single viral load test is not very meaningful; it must be considered along with other tests, such as CD4 count, or compared to past viral load tests to be helpful as an indicator of disease progression and immune health.