Question:

I would like to know what the implications are with having a high viral load and a CD4 count of 800? Does this mean I have been infected for a long time and never knew or is it evidence of co-infection. What about the 800 CD4 count if I have a high viral load?

Answer provided by:

Rodger MacArthur, M.D.
Wayne State University
Division of Infectious Diseases

Both the CD4 cell count and HIV RNA level are important in the management and prognosis of persons with HIV infection. The CD4 cell count is the best predictor of current risk of HIV-related disease. An HIV-uninfected person typically has a CD4 count of 800-1200 cells/μL. Risk for an HIV-related event increases when the CD4 cell count drops below 200 cells/μL, and greatly increases when the CD4 cell count drops below 50-100 cells/μL. The HIV RNA level correlates with the speed at which the CD4 cell count falls; the higher the HIV RNA level, the greater is the decline (measured in CD4 cells/μL/year lost). HIV RNA levels are highest during acute (early/recent) infection and late in the course of illness (when the CD4 cell count is low).

The loss of CD4 cells is not constant throughout the course of infection, but an approximate average over 5-7 years of infection for an individual with an HIV RNA level of 50,000-70,000 copies/mL would be about 50-70 cells/μL/year lost, from a starting CD4 cell count of about 800 cells/μL. An individual with HIV RNA levels above 100,000-200,000/mL might lose CD4 cells at twice that rate; an individual with HIV RNA levels of 10,000-20,000 might lose CD4 cells at half that rate. Note, however, that the correlation between HIV RNA levels and CD4 cell loss is not perfect; hence, individual differences can be quite dramatic. In other words, while an individual with a CD4 cell count of 800 cells/μL with a high HIV RNA level (more than 100,000 copies/ml) would be expected to fall below a CD4 cell count of 350 cells/μL within about 4 years, it is possible for it to take 6-10 years for the CD4 cell count to drop below 350 cells/μL. A better prediction of the average rate of CD4 cell loss per year for any given person can be obtained if there are multiple measurements made over several years.

It is important to know the CD4 percentage as well as the CD4 cell count. The CD4 percentage is measured directly by flow cytometry, whereas the CD4 cell count is derived from multiplying the total white blood cell (WBC) count by the percentage of lymphocytes in the blood (as a decimal) and multiplying that number by the CD4 percentage (as a decimal) from the flow cytometry result. For example, a person whose total WBC count is 6,000/μL, and who has 30% lymphocytes (from the WBC "differential") and who has a CD4% of 30% (from flow cytometry) would have a CD4 "count" of 540 cells/μL (6000/μL x 0.30 x 0.30). Fluctuations in the total WBC and/or the percent lymphocytes may make it appear that the CD4 count has changed dramatically as a result of HIV infection or antiretroviral therapy, when, instead, other factors may have been responsible. So, for instance, if the same individual with the CD4% of 30% had a concurrent bacterial pneumonia with a total WBC count of 15,000/μL and only 10% lymphocytes (because most of his WBCs were bacteria-fighting polymorphonuclear cells), his CD4 cell count would be 450 cells/μL (15,000/μL x 0.10 x 0.30).

In summary, a CD4 cell count of 800 with a "high" viral load may suggest a recent infection, with the likelihood of substantially lower CD4 cell counts within several more years. It would be important for the questioner to seek medical care from a physician expert in managing antiretroviral therapy, and to have his CD4 cell count and HIV RNA level determined every 3-4 months.

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