Which laboratory test is used to assess the immune function of HIV patients?

The CD4 cell count test is vital for assessing the immune function of HIV patients because it specifically measures the number of CD4 T lymphocytes in the blood. CD4 cells are crucial for the immune response, and their count reflects the immune system's health. In individuals living with HIV, the virus attacks these cells, leading to a decrease in their numbers. A higher CD4 count indicates a healthier immune system and better ability to fight off infections, whereas a lower count signifies immunosuppression and increased vulnerability to opportunistic infections.

In contrast, other tests like the complete blood count evaluate overall blood health, including red and white blood cells but do not specifically indicate immune function related to HIV. The viral load test measures the amount of HIV in the blood, which is important for understanding how well the virus is controlled but does not directly assess immune function. The HIV RNA test also measures the virus's presence but does not provide insights into the immune system's status. Therefore, the CD4 cell count is the most relevant indicator of immune function in HIV patients.