Concordance and discordance between maternal and newborn drug test results.

BACKGROUND Screening for substance use is recommended during pregnancy and many clinicians rely on urine drug screening to identify newborns at potential risk for withdrawal. OBJECTIVE To determine the concordance and discordance rates between maternal and neonatal drug testing at or near the time of delivery. STUDY DESIGN This retrospective chart review was performed at a single institution that employs universal testing for those who consent. Results of maternal and neonatal urine drug testing via immunoassay at delivery were compared. RESULTS Of 1,573 singleton pregnancies, 233 (14.8%) mothers tested positive for any substance and 102 (43.8%) of their newborns had concordant positive tests. Of the 285 positive maternal tests for individual substances, 133 (46.7%) were concordant with newborn test results. After removing iatrogenic positives, there were 84 truly discordant pairs representing 5.9% of the total cohort of test pairs, but 29.5% of the pairs with maternal positive tests. When considering the outcome of a newborn positive test, the overall sensitivity and specificity for the maternal test was 21.1% and 85.8%, respectively. The positive and negative predictive values were 46.7% and 96.4%, respectively. After excluding iatrogenic positive tests, the sensitivity and specificity for maternal testing was 97.8% and 99.4%, respectively and the negative predictive value of maternal testing for all substances approached 100% (Table 3). Eleven pairs of twins had at least one twin with a positive drug test and of these, six twin pairs (54.5%) had drug tests that were discordant from each other. CONCLUSION There is a high rate of iatrogenic discrepancy in maternal and neonatal drug testing. After adjusting for iatrogenic positive tests, the negative predictive value of maternal testing is high. Many discrepancies, such as those in twins, remained unexplained by medication administration and potential reasons for these discrepancies warrant further investigation.