CD4+ T cell count as a tool to monitor HIV progression & anti-retroviral therapy.

The CD4+ T lymphocytes are the crucial cells in the orchestral events in forming immune response to the foreign antigen and it is also the primary target cells for human immunodeficiency virus (HIV). The progressive loss of these cells eventually results in the loss of an ability to mount desirable immune response to any pathogen and death of the patients in the terminal stage of HIV infection, i.e., acquired immune deficiency syndrome (AIDS). The longitudinal monitoring of CD4+ counts is used as a monitoring tool for disease progression and effectiveness of antiretroviral treatment. Various methods are being used for determination of absolute CD4+ T lymphocytes from the peripheral blood. To date, the flow cytometry is considered as the gold standard. Different modifications have been tried in the conventional flow cytometry to increase accuracy and cost-effectivity especially for adapting in resource-poor settings. Principles of the conventional and modified methodologies are discussed. The non-flow cytometric methodologies are also there that might be available soon widely. The choice of the methodology should depend upon the purpose of the assay, the age group of the patients, sample turnover and available resources. Importance of maintaining both internal and external quality control systems in every laboratory performing CD4 count estimation are discussed.