Detection of human immunodeficiency virus type 1 p24 antigen and plasma RNA: relevance to indeterminate serologic tests

BACKGROUND : Most enzyme immunoassay‐reactive specimens producing indeterminate Western blot results belong to individuals who are not infected with human immunodeficiency virus type 1 (HIV‐1). However, a small percentage may correspond to early seroconversion or advanced disease, at which stage partial reactivity on Western blot may be observed. STUDY DESIGN AND METHODS : To determine the utility of HIV‐1 p24 antigen and cell‐free RNA detection for the resolution of Western blot‐indeterminate serologic results, several types of enzyme immunoassay‐positive, sero‐indeterminate specimens were analyzed. Samples were obtained from infected individuals at the time of seroconversion (n = 20), from patients with AIDS (n = 2), as specimens from clinical samples obtained for diagnostic testing (n = 57), from blood donors producing persistent indeterminate results (n = 47), and from random blood donors (n = 72). RESULTS : HIV‐1 p24 antigen was detected in 10 of 20 specimens collected from 9 of 12 individuals who seroconverted and in 2 of 2 AIDS patients. HIV‐1 plasma RNA was positive in 22 of 22 samples from those 14 individuals. All of 57 diagnostic specimens and 47 samples obtained from persistently indeterminate donors were negative for HIV‐1 p24 antigen and plasma HIV‐ 1 RNA. One of 72 blood donor specimens was positive for HIV‐1 plasma RNA and had borderline reactivity for p24 antigen. CONCLUSION : The detection of plasma RNA appears to be sensitive and specific; negative test results may be used to identify false‐positive serologic reactions. The detection of p24 antigen and plasma RNA can also be used to confirm HIV‐1 infection in persons with indeterminate serologic results associated with early seroconversion or late‐stage disease.