Analysis of diurnal variation of lymphocyte subsets in healthy subjects in the Caribbean, and its implication in HIV monitoring and treatment.

Absolute values of the lymphocyte subsets are known to be influenced by various biological factors. We set out to determine if diurnal variations in lymphocyte subsets occur in our population. A prospective study was done on 25 randomly chosen healthy subjects. Persons were enrolled for the early morning to mid afternoon study i.e. 8:30, 12:30 and 15:30. In a second study, samples were collected at hourly intervals from 08:30 to 12:30. The EDTA samples were analyzed for lymphocyte subsets by flowcytomery. In the first study, the results have shown that there was a progressive increase in CD4 cell count throughout the day, while CD8 and CD19 cell counts increased between 08:30am and mid-day and then there was no further change between midday and mid afternoon. CD56 was uniform throughout the whole day. As most clinics and venesections take place in the morning, the aim of the second part of the study was to focus on the nature of the changes observed in the morning to midday phase. The results have shown that there were no significant changes in the lymphocyte subset counts before 11:30, thereafter there was a progressive increase in all of the lymphocyte subsets between 11:30 and 12:30 except for the CD56 cell count. This study has shown that diurnal rhythms influence the lymphocyte subsets in a normal population. This may have major implications in the use of CD4 subset analysis in the management of HIV infected persons as an indicator for initiation of treatment. In our setting. pending the results of diurnal variation studies on PLWHA, we have set the latest blood collection time at 11:30 am.