Summary of samples used in the study, including plasma and dried blood spots (DBS).

aHIV negative specimens collected from pregnant women in Tanzania used for assay specificity analysis; b Plasma-matched DBS samples collected from voluntary counseling and testing (VCT) sites in Ho Chi Minh City enrolled in an HIV-1 threshold survey; cPlasma-matched DBS samples collected from patients enrolled in the Nigeria HIVDR perspective monitoring survey at 12-15 months after commencement of first line antiretroviral therapy; d Not available.