Challenges in implementing CD4 testing in resource-limited settings.

The scale-up of HIV antiretroviral therapy in recent years has led to a rapid increase in CD4 and CD4% count capacity to meet the diagnostic needs of staging and monitoring disease progression and treatment efficacy in adults and infants. The speed of implementation of this technology has been unrivalled in recent years and has met challenges with technology selection, laboratory infrastructure development, human resource limitations, cost-effectiveness, instrument maintenance, and ensuring testing access and quality. The lessons learned from dealing with these challenges have helped strengthen existing laboratory systems for other diagnostics. They may also facilitate the implementation of new diagnostics in future.