The absolute CD4 count, also known as the CD4 cell count or T-helper cell count, is a laboratory test that measures the number of CD4 T-cells in a sample of blood. CD4 T-cells are a type of white blood cell that play a critical role in the immune system’s response to infections, particularly viral infections like HIV.
In HIV infection, the virus targets and destroys CD4 T-cells, which can lead to a weakened immune system and an increased risk of developing opportunistic infections. Monitoring the absolute CD4 count is an important part of HIV management, as it can help healthcare providers track the progression of the disease and determine when to initiate or adjust antiretroviral therapy (ART).
The absolute CD4 count is typically reported as the number of CD4 T-cells per microliter (µL) of blood. Normal CD4 T-cell counts in adults range from 500 to 1,500 cells/µL. In individuals with HIV, the absolute CD4 count is used to determine the stage of the disease and the level of immunosuppression. The Centers for Disease Control and Prevention (CDC) classifies HIV infection into four stages based on the CD4 T-cell count:
- Stage 1: CD4 count ≥ 500 cells/µL
- Stage 2: CD4 count 200-499 cells/µL
- Stage 3: CD4 count < 200 cells/µL or the presence of an AIDS-defining illness
- Stage unknown: no information available to determine the stage
ART is typically recommended for individuals with an absolute CD4 count below 500 cells/µL or those who have developed an opportunistic infection, regardless of their CD4 count. ART is designed to suppress the replication of the virus, which can help prevent further damage to the immune system and reduce the risk of developing opportunistic infections.
In addition to HIV, the absolute CD4 count can also be used to monitor other conditions that affect the immune system, such as autoimmune disorders, certain cancers, and immunodeficiencies. However, the reference ranges for CD4 T-cell counts in these conditions may vary depending on the specific disease and the individual’s age and overall health.