Sensitivity and specificity of prenatal urine drug screening using national institute of drug abuse cutoff levels with the florescence polarization immunoassay
OBJECTIVE: The purpose of this study was to determine the sensitivity and specificity of prenatal urine drug screening with florescence polarization immunoassay (FPIA) using cutoff concentrations specified by the National Institute of Drug Abuse (NIDA). METHODS: One hundred eighty-two urine samples were collected from pregnant women during their first prenatal visit. The urine samples were initially analyzed by FPIA. Drug levels from positive screens were compared to specified NIDA cutoff concentrations: Amphetamines 1000 ng/ml Cannabinoids 50 ng/rnl Cocaine metabolite 300 ng/ml Opiates 300mg/ml Phencyclidine 25 ng/ml Drug concentrations below these levels were considered negative by NIDA standards. All samples were then analyzed by gas chromatography and mass spectroscopy to determine true drug prevalence. Sensitivity and specificity were calculated for FPIA using NIDA cutoff levels and FPIA without NIDA cutoff levels. RESULTS: The sensitivity, specificity, positive predictive value, and negative predictive value for FPIA using NIDA cutoff concentrations were 43.3%, 94.7%, 61.9%, and 89.4%, respectively. The sensitivity, specificity, positive predictive value, and negative predictive value for FPIA without NIDA cutoff concentrations were 100%, 76.3%, 45.5%, and 100%, respectively. CONCLUSION: Using NIDA cutoff levels to interpret prenatal urine samples screened by FPIA yielded good specificity with poor sensitivity. Interpreting the FPIA without the NIDA cutoff levels increased the detection rate as expected but decreased the positive predictive value.
