title: Field performance of a thin-layer chromatography assay for detection of nevirapine in umbilical cord blood.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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 dollars vs. 50 dollars), and the proportion of false results was acceptable (11%). As population NVP coverage increased, cost-efficiency improved and error rate dropped substantially.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Centre for Infectious Disease Research in Zambia, Lusaka, Zambia. bchi@cidrz.org
authors.forename: Benjamin H
authors.initials: BH
authors.lastname: Chi
authors.forename: Alison
authors.initials: A
authors.lastname: Lee
authors.forename: Edward P
authors.initials: EP
authors.lastname: Acosta
authors.forename: Larry E
authors.initials: LE
authors.lastname: Westerman
authors.forename: Moses
authors.initials: M
authors.lastname: Sinkala
authors.forename: Jeffrey S A
authors.initials: JS
authors.lastname: Stringer
mesh_terms: D000465:Algorithms; D019380:Anti-HIV Agents / Q000493:pharmacokinetics* / Q000627:therapeutic use; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer / Q000191:economics; D003362:Cost-Benefit Analysis; D005260:Female; D005312:Fetal Blood / Q000378:metabolism*; D006678:HIV; D015658:HIV Infections / Q000378:metabolism* / Q000517:prevention & control / Q000635:transmission; D006801:Humans; D007231:Infant, Newborn; D018445:Infectious Disease Transmission, Vertical / Q000517:prevention & control; D019829:Nevirapine / Q000493:pharmacokinetics* / Q000627:therapeutic use; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000378:metabolism* / Q000517:prevention & control; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D016896:Treatment Outcome; D015024:Zambia
chemical_list: D019380:Anti-HIV Agents; D019829:Nevirapine