Question

Why are CD4 levels measured?

Answer 1

This is a direct measurement of the activity of something called your adaptive immune system.

Explanation:

CD4 (cluster of differentiation 4) is a glycoprotein specific for a special cell type in your immune system known as the helper T cell, which is probably the most important cell in "adaptive immunity." The T helper cells signal B cells to produce antibodies against pathogens. Without helper T cells, the immune system cannot produce enough antibodies to fight infection. This is a problem because it means that usually minor infections, such as the common cold, could become life threatening.

We can measure the levels of CD4 to roughly determine the number of helper T cells in an individual. Since we know the range of helper T cells that would be considered "normal" in a healthy person, we can use it as and indicator for how well the immune system is functioning.

Most of the time, we measure CD4 levels in people with HIV/AIDS because this disease directly targets the helper T cells and kills them. The longer a person has HIV/AIDS, the less helper T cells they have to fight infection.

Thus, we can use CD4 levels to measure how severely a person's immune system has been compromised, and therefore, how susceptible they are to new infections.

Hope this helps!

~AP