Field Performance of a Thin-Layer Chromatography Assay for Detection of Nevirapine in Umbilical Cord Blood

Abstract

Purpose: Although cord blood surveillance can measure the effectiveness of nevirapine (NVP)-based programs for the prevention of mother-to-child HIV transmission (PMTCT), it requires the ability to detect nevirapine in plasma. At present, the only validated method is high-performance liquid chromatography (HPLC), a technique poorly suited for most resource-constrained settings. Method: We evaluated the field performance for a simple and inexpensive thin-layer chromatography (TLC) assay for NVP detection. We developed a conditional probability model to compare 2 testing algorithms: HPLC alone, and TLC screening followed by HPLC confirmation of negative results. Results: When compared to HPLC, sensitivity of TLC was 0.67 (95% confidence interval [CI] 0.49–0.84) and specificity was 0.84 (95% CI 0.69–0.95). In this sample — where overall NVP coverage was 49% — positive predictive value was 0.80 and negative predictive value was 0.72. At baseline with population NVP coverage of 33%, cost per specimen was lower in the TLC-HPLC testing algorithm ($40 vs. $50), and the proportion of false results was acceptable (11%). As population NVP coverage increased, cost-efficiency improved and error rate dropped substantially. Conclusion: TLC is reasonably sensitive and specific for NVP detection. A 2-step testing algorithm incorporating TLC and HPLC provides cost-efficiency at little expense to test performance.