Absolute T4 cell count: Also called the “absolute CD4+ count.” This number is calculated from the results of three different blood tests. The absolute T4 count is the most common surrogate marker (a lab measurement that can show indirectly the effect of a treatment on a disease) used for people with HIV.
T4 cells are the white blood cells most likely to decrease in people with HIV. These cells play an important role in controlling infections. T4 cells die about 24 to 36 hours after being infected with HIV. Your body is able to replace these cells and keep HIV in check for years. However, at some point your immune system will start to lose ground. Figuring out the number of T4 cells in a sample of blood can give you an idea of how your immune system is doing. Knowing your T4 count can help you decide when to take action and what to do.
The normal range of T4 counts can vary from one lab to another, depending on which procedures are used. For example, some labs may use 450-1150 cells per cubic millimetre as the normal range for adults; others may use 550-1250. Any single count of T4 cells is not a sure sign of how your immune system is doing. Two T4 cell counts done on samples of blood drawn from the same person twelve hours apart can be very different from each other. If one T4 cell count is way out of line with the pattern shown in the last several tests, it may be a good idea to get another test done. Your T4 cell count shows only one part of how your immune system is functioning. Always consider it as part of a bigger picture. Look for trends over time, rather than focusing on a specific result.
T4 (or CD4+) percentage: This measures the percentage of T4 cells compared to the total number of lymphocytes in your blood. T4 cells usually make up between 31 and 49 per cent (about one-third to one-half) of the total number of your lymphocytes. As the number of your T4 cells drops, it makes up less and less of the total number of lymphocytes. This test is used together with your absolute T4 cell count to get a more complete picture of your immune system.
Absolute T8 count: Also called the “absolute CD8+ count.” This number is calculated from the results of three different blood tests. The absolute T8 count is another sign of whether people have HIV. People with HIV often have T8 counts above the normal range.
As with T4 counts, the normal range of T8 counts can vary from lab to lab, depending on which procedures are used.
T8 (or CD8+) percentage This measures the percentage of T8 cells compared to the total number of lymphocytes in your blood.