Counting CD4 lymphocyte numbers (the “CD4 count”) is an important part of monitoring HIV infection. A progressive downward trend in CD4 cells reflects disease progression and decreased life expectancy, even in the absence of symptoms.
Epidemiological studies have firmly correlated distinct ranges of CD4 cell counts with risk of particular opportunist infections. Recent data show that monitoring either the absolute CD4 lymphocyte count or the ratio of CD4 to CD8 cells, the 4:8 ratio, are both equally good at monitoring progression in HIV
infection. 2 microglobulin and neopterin are molecules shed from activated lymphocytes; serum levels increase with progressive HIV infection and can be a useful adjunct to CD4 counts in monitoring.
CD4 lymphocyte numbers have a diurnal variation and delays in the sample reaching the immunological laboratory (for example, when a sample is held overnight) also cause profound changes. Because CD4 lymphocyte counting is a lengthy process, most consistent results are obtained when samples are taken at a set time in the morning and sent straight to the lab. In case of unavoidable hold ups, samples should not be
refrigerated.
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