[The pitfalls of lymphocyte immunophenotyping during HIV infection]

Preferential infection of CD4+ lymphocytes by HIV, related to both direct and indirect mechanisms, leads to progressive decrease in this population. A CD4 lymphocyte count has become the preferential test for monitoring the infection. Thus, a flow cytometry laboratory handles a great number of phenotyping prescriptions that require accuracy and precision. The technical and biological parameters involved are listed, and some rules for interpretation of results given. Because no standardization exists and because cytometers are not automated, there is often great variability between laboratory results. We show that variability can be decreased by the use of correct procedures for analysis on the cytometer (especially for fluorescence interpretation). On the other hand, many biological factors have a significant effect on the results. A list of these factors is given: circadian rhythm, other infectious diseases and drugs. Lastly, the distribution of values in normal subjects is reported. The wide range shows that results from a patient must be compared with previous values to determine the course of the infection. These data would help in defining and interpreting results.