Drugs of Abuse Screen on Meconium
Drug abuse during pregnancy is associated with significant perinatal complications including a high incidence of stillbirths, meconium-stained fluid, premature rupture of membranes, maternal hemorrhage due to abruption placenta or placenta praevia, and fetal distress. Drug exposed neonates have increased mortality and morbidity due to asphyxia, prematurity, low birthweight, hyaline membrane disease, infection, aspiration pneumonia, cerebral infarction, abnormal heart and breathing patterns, and drug withdrawal.
When a fetus is exposed to drugs, the fetus excretes drug into bile and amniotic fluid. Drug accumulates in meconium directly from bile or through swallowing of amniotic fluid. Meconium is first detected in the fetal intestine at the 10th to 12th week of gestation, and slowly moves into the colon by the 16th week of gestation. The presence of drugs in meconium is believed to be indicative of in utero drug exposure during the final 4 to 5 months of pregnancy. This is a longer historical measure than can be detected by urine drug screens.
Meconium is a dark green, viscous substance composed of intestinal secretions, desquamated squamous cells, lanugo hair, bile pigments, pancreatic enzymes and blood. It is the first intestial discharge from newborns. Meconium is usually passed by full-term newborns within 24 to 48 hours. Low birth weight newborns may not pass their first meconium until 3 days or more. The transition from a dark green to yellow color indicates the change from meconium to neonatal stool.
Meconium drug testing begins with an immunoassay. Positive results are confirmed and quantitated by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Drug confirmation is necessary because some prescribed or over the counter medications cross-react and produce a positive screening result.
This test Identifies amphetamines, (including methamphetamine), opiates, cocaine and marijuana in meconium specimens. Cutoff concentrations are:
- Amphetamines by ELISA: 100 ng/g
- Methamphetamine by ELISA: 100 ng/g
- Benzoylecgonine (cocaine metabolite) by ELISA: 100 ng/g
- Opiates by ELISA: 100 ng/g
- Tetrahydrocannabinol carboxylic acid (marijuana metabolite) by ELISA: 20 ng/g
- Phencyclidine by ELISA: 20 ng/g
The limit of quantitation varies for each of these drug groups.
- Amphetamines: >100 ng/g
- Methamphetamines: >100 ng/g
- Cocaine and metabolite: >100 ng/g
- Opiates: >100 ng/g
- Tetrahydrocannabinol carboxylic acid: >20 ng/g
- Phencyclidine (PCP): >20 ng/g
Reference value is no drug detected in meconium.
Meconium is collected directly from the diaper of the neonate. Specimen requirement is approximately 1 gram of meconium shipped in a stool container. Grossly bloody specimens are rejected. Refrigerated specimens are stable for 24 hours. After 24 hours, cocaine and cannabinoid concentrations decrease. Frozen specimens are stable for 14 days.
If heroin use is suspected, specimen must be sent frozen to prevent loss of the heroin metabolite, 6-monoacetylmorphine (6MAM). When refrigerated, a significant percentage of 6MAM will convert to morphine in fewer than 24 hours.
Unless meconium specimen is frozen, cocaine metabolite will degrade within 72 hours of collection.
References
Ostrea EM Jr: Understanding drug testing in the neonate and the role of meconium analysis. J Perinat Neonatal Nurs 2001 Mar;14(4):61-82; quiz 105-106
2. Ostrea EM Jr, Brady MJ, Parks PM, et al: Drug screening of meconium in infants of drug-dependent mothers; an alternative to urine testing. J Pediatr 1989 Sep;115(3):474-477
3. Ahanya SN, Lakshmanan J, Morgan BL, Ross MG: Meconium passage in utero: mechanisms, consequences, and management. Obstet Gynecol Surv 2005 Jan;60(1):45-56; quiz 73-74
4. Langman L. Meconium testing provides indication of drug exposure. Clinical & Forensic Toxicology News. AACC/CAP Educational Newsletter for Toxicology Laboratories, Dec 2006.
