Methods of analysis
Screening meconium for drugs of abuse
Radioimmunoassay (RIA), fluorescence polarisation immunoassay (FPIA) and enzyme multi plied immunoassay technique (EMIT) have all been described as useful analysis methods for screening meconium specimens. Overall, FPIA and RIA have been shown to be more sensitive than EMIT for the detection of cocaine metabolite (benzoylecgonine) in spiked meconium samples. Other comparative research has shown that the CAC Cocaine RIA (DPC Corporation, CA, USA) is the most sensitive assay for meconium screening. Presumably this is because there is significant cross-reactivity with cocaine which is often present in meconium, compared with various other immunoassays which are specific for benzoylecgonine. The original work carried out on meconium used radioimmunoassay for the detection of drugs. In the 1980s, Enrique Ostrea (Department of Pediatrics, Hutzel Hospital, Wayne State University, Detroit, MI, USA) became the first researcher to publish and patent procedures for the screening of drugs of abuse in meconium. In his original method, for each analysis 0.5 g of meconium was collected directly from the diaper. The sample was mixed with distilled water and then concentrated hydrochloric acid, and this homogenate was filtered through glass wool. The filtrate was centrifuged and an aliquot of the supernatant was tested for morphine (heroin metabolite) and benzoylecgonine (cocaine metabolite) using Abuscreen RIA kits. The recovery from drug-free meconium for benzoylecgonine and morphine was 70–105% and 8–97%, respectively. For cannabinoids, methanol was added to meconium. The sample was mixed and allowed to stand at room temperature for 10 minutes then centrifuged. An aliquot of the supernatant was tested for the cannabinoid metabolites by RIA. To date, many other screening procedures have been developed for cocaine, opiates, am feta mines, marijuana, and phencyclidine. The use of ELISA technology has allowed the screening profiles to be expanded since there is no matrix effect normally associated with meconium testing. Direct ELISA screening methods exist for the determination of other drugs such as barbiturates, benzodiazepines, fluoxetine, sertraline, propoxyphene, synthetic opioids, LSD, nicotine and its metabolites (cotinine, trans-3-hydroxy cotinine) in meconium.
