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In order to be at ease interpreting your CD4 test results when you visit your physician, it is important to understand the role of your CD4 in your immune system.
As mentioned in the section What is the difference between HIV and AIDS?, HIV is a virus. The main goal in life of a virus is to reproduce (create new infectious virus). In order that the HIV virus may reproduce it requires the machinery found in a human cell – it will not survive in isolation. As an example – look at the influenza (flu) virus that requires cells found at the level of the respiratory tract (lungs). The HIV virus has a preference for the immune system cells called CD4 (T4 in some publications). The role of your CD4 cells is to co-ordinate your immune system. In the process of using your CD4 cells to further its own reproduction, HIV ends up destroying its host (CD4) and thereby is able to cause a weakening of the immune system.
It is possible to monitor the number of CD4 cells present via a simple blood test. This test is termed the “CD4 cell count”. The range of CD4 values is quite large – when the CD4 count is above 500, the immune system is considered to be in good health and able to adequately protect an individual from infections. As HIV progresses, CD4 cell counts tend to decline unless of course the progression is arrested by antivirals (anti-HIV medications).
When the CD4 cell counts fall below 200 there is a greater risk of infections and/or complications related to HIV. CD4 cell counts below 200 are an indication of a compromised immune system.
So, CD4 cell counts are one of the methods your physician employs to evaluate the state of health of your immune system. Your physician will usually suggest that you undergo this blood test on a regular basis (approximately every 3 months – give or take!).
There are not only absolute numbers when it comes to evaluating CD4 and your immune system. Your physician may monitor (via the same blood test) the percentage of CD4 cells and the ratio of immune cells – all provided in your routine immune profile. Taken together, these values assist you and your physician in evaluating the overall state of your immune system (seeing as there are several other types of immune cells in our body). Speak to your physician regarding your most recent results and the overall trends of your immune system.
In addition, it is extremely important to understand that the number of CD4 cells varies tremendously from one day to the next, and even within the same day. The results taken during one blood test are like a snapshot of your immune system at that particular moment. It is for this reason that it is much more useful to COMPARE results from one blood test to the next and evaluate the trends in your immune system. What is important to evaluate (with several sequential tests in hand) whether your immune system is stable, getting stronger or weaker over time. Of note! One should never make decisions based on one single blood test (repeat and compare when results are unexpectedly different), nor should decisions be made based on absolute CD4 cell counts alone. CD4 cell numbers may fall without there being an impact on the overall health and stability of your immune system. In conclusion, your immune profile and its various elements when taken together and compared with your previous analyses will permit you and your physician to determine your current immune health status.