Evaluation of an ultrasensitive p24 antigen assay as a potential alternative to human immunodeficiency virus type 1 RNA viral load assay in resource-limited settings.

An inexpensive enzyme-linked immunosorbent assay method for human immunodeficiency virus type I quantitation, ultrasensitive p24 antigen assay (Up24), was compared with RNA viral load assay (VL). Up24 had 100% sensitivity of detection at a viral load of greater than or equal to30,000, with sensitivity of 46.4% at a viral load of <30,000 (232 specimens from 65 seropositive subjects). The assay was highly reproducible, with excellent correlation between duplicates and among three laboratories.