RT Journal Article SR Electronic T1 In utero drugs of abuse exposure testing for newborn twins JF Journal of Clinical Pathology JO J Clin Pathol FD BMJ Publishing Group Ltd and Association of Clinical Pathologists SP 259 OP 261 DO 10.1136/jcp.2009.067595 VO 63 IS 3 A1 Ping Wang A1 Claudia P Molina A1 Joyce E Maldonado A1 David W Bernard YR 2010 UL http://jcp.bmj.com/content/63/3/259.abstract AB This report describes testing of a case of in utero drugs of abuse exposure in which discordant results were seen between urine and meconium, and between twin meconium samples. The discordance between urine and meconium could be explained by the differences in detection window, threshold concentration and screening technology, and the discordance between dizygotic twin meconium samples could be explained by the differences in drug diffusion and placental and fetal biotransformation of drugs. The meconium sample of one twin screened negative for benzodiazepines was reported positive in the confirmation assay with higher sensitivity and a lower cut-off concentration. Negative screening results of drugs of abuse should be interpreted with caution, taking into account matrix type, reactivity of drugs in the assay and cut-off concentration. If screening results are inconsistent with each other or with the clinical scenario, confirmation testing using more sensitive and specific methods with lower cut-offs is warranted.