MATHEMATICAL models and statistical evaluations are often used to explain biologic phenomena. The acquired immunodeficiency syndrome (AIDS) is no exception. Through the years of studying the human immunodeficiency virus (HIV) and its effect on the immune system, investigators have emphasized counting CD4+ cells and CD8+ cells and/or measuring p24 antigen levels or, more recently, the viral RNA content of the plasma. What is known, but not always appreciated, is the limited information that may be reflected by these parameters when measured in the blood. Peripheral blood lymphocyte numbers represent only a small percentage (3%) of the total white blood cells in the body,1 and plasma virion content is just a portion of the total HIV virions, which are concentrated primarily in lymphoid organs.2 Thus, in several experimental systems, plasma viral RNA may not reflect the actual viral load. Moreover, although CD4+ cell numbers may be helpful in predicting
Levy JA. Surrogate Markers in AIDS Research: Is There Truth in Numbers? JAMA. 1996;276(2):161–162. doi:10.1001/jama.1996.03540020083035
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