Immune status monitoring of HIV/AIDS patients in resource-limited settings: a review with an emphasis on CD4+ T-lymphocyte determination.

CD4 T-lymphocytes play a vital role in maintaining the integrity of the human immune system. They are also the primary target cells for human immunodeficiency virus (HIV). The progressive depletion of these cells eventually results in weakening of the host's immune ability to fight against any pathogen, thus rendering the host susceptible to infections and leading ultimately to death of patients in the terminal stage of acquired immune deficiency syndrome (AIDS). Although several clinical and laboratory parameters have been used for monitoring disease progression and the effectiveness of HIV antiretroviral therapy (ART), it is the simple measurement of CD4+ T-lymphocytes that remains the single and most important parameter for management of HIV-infected patients in resource-limited settings. To date, flow cytometer is considered to be the most accepted technology for both percentage and absolute CD4+ T-lymphocyte determination because of its accuracy, precision and reproducibility. However, flow cytometer based CD4 testing is relatively expensive, complex and thus technically demanding. Simple innovative approaches applicable to the conventional flow cytometric system and new technologies have been successfully developed to increase cost saving especially for use in resource-challenged settings. Principles of the existing dual- and single-platform approaches as well as several affordable CD4 measurement technologies are discussed along with both internal and external quality control systems in the management of laboratories performing CD4 testing.