β₂-microglobulin, HIV-1 p24 antibody and acid-dissociated HIV-1 p24 antigen levels: Predictive markers for vertical transmission of HIV-1 in pregnant Ugandan women

Objectives: To evaluate the clinical utility of plasma β₂-microglobulin (β₂M) levels, acid-dissociated HIV-1 p24 antigen, and HIV-1 p24-antibody titers in predicting HIV-1 vertical transmission in 227 HIV-1-infected Ugandan pregnant women. Design: Plasma β₂M levels, acid-dissociated HIV-1 p24-antigen positivity, and HIV-1 p24-antibody titers were determined using commercial enzyme immunoassays (EIA) in a Ugandan cohort of 52 HIV-1-seropositive transmitting mothers, 175 HIV-1-seropositive non-transmitting mothers, and 52 seronegative mothers within 6 weeks prior to delivery. Results: Transmitter mothers had significantly higher plasma concentrations of β₂M (1.80 ± 1.13mg/l) than non-transmitter seropositive mothers (1.32 ± 0.81 mg/l; P=0.0013). Similarly, a significantly higher proportion of transmitter mothers had detectable p24 antigen than non-transmitter mothers [six out of 51 (11.8%) versus six out of 173 (3.5%); P=0.03]. Compared with the vertical transmission rate of 23% in the seropositive group, the positive predictive values of a β₂M level > 1.5 mg/l or detectable HIV-1 p24 antigen for vertical transmission were 34 and 50%, respectively. Five of six (83.3%) seropositive mothers with both a β₂M level > 1.5 mg/l and detectable p24 antigenemia transmitted HIV-1 infection to their infants compared with 25 of 124 (20.2%) seropositive mothers with values below the cut-off values for both tests (P=0.00249). However, β₂M was not found to be a significant independent predictor of vertical transmission when analyzed in a multivariate model with p24 antigenemia. There was no significant difference in HIV-1 p24-antibody titers in transmitter mothers versus non-transmitter mothers (P=0.299). Conclusion: β₂M levels and acid-dissociated HIV-1 p24-antigen assays may be used to predict which HIV-1-infected pregnant women are at greatest risk for vertical transmission. However, only the p24-antigen test was independently predictive of vertical transmission and its clinical utility is limited.