Comparison of point-of-care versus laboratory-based CD4 cell enumeration in HIV-positive pregnant women

INTRODUCTION Early initiation of antiretroviral therapy (ART) in eligible pregnant women is a key intervention for prevention of mother-to-child transmission (PMTCT) of HIV. However, in many settings in sub-Saharan Africa where ART-eligibility is determined by CD4 cell counts, limited access to laboratories presents a significant barrier to rapid ART initiation. Point-of-care (POC) CD4 cell count testing has been suggested as one approach to overcome this challenge, but there are few data on the agreement between POC CD4 cell enumeration and standard laboratory-based testing. METHODS Working in a large antenatal clinic in Cape Town, South Africa, we compared POC CD4 cell enumeration (using the Alere Pima(TM) Analyzer) to laboratory-based flow cytometry in consecutive HIV-positive pregnant women. Bland-Altman methods were used to compare the two methods, including analyses by subgroups of participant gestational age. RESULTS Among the 521 women participating, the median gestational age was 23 weeks, and the median CD4 cell count according to POC and laboratory-based methods was 388 and 402 cells/µL, respectively. On average, the Pima POC test underestimated CD4 cell count relative to flow cytometry: the mean difference (laboratory test minus Pima POC) was 22.7 cells/µL (95% CI, 16.1 to 29.2), and the limits of agreement were -129.2 to 174.6 cells/µL. When analysed by gestational age categories, there was a trend towards increasing differences between laboratory and POC testing with increasing gestational age; in women more than 36 weeks' gestation, the mean difference was 45.0 cells/µL (p=0.04). DISCUSSION These data suggest reasonable overall agreement between Pima POC CD4 testing and laboratory-based flow cytometry among HIV-positive pregnant women. The finding for decreasing agreement with increasing gestational age requires further investigation, as does the operational role of POC CD4 testing to increase access to ART within PMTCT programmes.