Thirty-five years of CD4 T-cell counting in HIV infection: From flow cytometry in the lab to point-of-care testing in the field.

CD4 T-cell counting was introduced in clinical laboratories shortly after the discovery of the human immune deficiency virus (HIV) in the early eighties. In western clinical laboratories, improvements in the CD4 T-cell counting methods were mainly driven by progress in the field of flow cytometry and immunology. In contrast, the development of dedicated CD4 T-cell counting technologies were needs driven. When antiretroviral treatment (ART) was made available on a large scale by international Acquired Immune Deficiency Syndrome (AIDS) relief programs to HIV+ patients living in low income countries in 2003, there was a distinct need for simplified and affordable CD4 T-cell counting technologies. The first decade of 2000, several compact flow cytometers appeared on the market, mainly to the benefit of low income countries with limited resources. More recently, however, portable point-of-care (POC) CD4 T-cell counting devices have been developed especially to improve access to affordable monitoring of HIV+ patients in low income countries. The accuracy of these POC instruments is not yet very well documented as many are still under development and clinical validation but preliminary evidence is encouraging. The new HIV treatment guidelines released by the World Health Organization in 2016 give CD4 T-cell counting a less central role in the management of HIV infection. It is, therefore, to be expected that CD4 T-cell counting will be phased out as a tool to assess eligibility of HIV+ patients for ART in the future. However, CD4 T-cell counting will remain a valuable tool for directing treatment against opportunistic infections.