What is the role of urine toxicology assays in the diagnosis of neonatal abstinence syndrome (NAS)?

Updated: Dec 20, 2017
  • Author: Ashraf H Hamdan, MD, MBBCh, MSc, MRCP, FAAP; Chief Editor: Santina A Zanelli, MD  more...
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Answer

Note the following:

  • Urine was traditionally the specimen of choice for neonatal drug testing, although collection is difficult. The adhesive for the collection bag causes skin irritation and frequently fails to adhere. Another disadvantage is the short detection window; urine provides maternal drug use data only for a few days prior to delivery.

  • Urine toxicology screening is useful for clinical and research purposes. Urinary excretion of metabolites may be detectable only for a few days (eg, benzoylecgonine) to a few weeks (eg, cannabinoids). One cannot expect to ascertain early pregnancy use or even relatively recent use if the metabolite concentration does not reach the detection threshold.

  • Urine is relatively easy to obtain, requires minimal preparation (provided samples are not contaminated by meconium or feces), and can be analyzed using numerous laboratory techniques. Although urine samples generally contain a higher drug concentration than serum samples, the detection of compounds depends on obtaining an appropriate sample as close as possible to birth and also depends on the timing of maternal drug ingestion prior to delivery.

  • These tests detect recent use of cocaine and its metabolites, amphetamines, marijuana, barbiturates, and opiates. Cocaine can be detected in urine 6-8 hours after use in the mother and as long as 48-72 hours after use in the newborn. Alcohol is detectable in neonatal urine for 6-16 hours after the last maternal ingestion.

  • Detection of drugs depends on many variables, including individual drug metabolism, hydration status of the subject, route of administration, and frequency of ingestion.

  • No drugs are known to crossreact with the immunoassays for cocaine and marijuana. Several over-the-counter remedies and herbal preparations may contain ephedrine and phenylpropanolamine (recalled from US market), which can produce false-positive enzyme immunoassay test results for amphetamines. Therefore, confirmatory testing is required.

  • Immunoassay for opiates does not distinguish between codeine, morphine, or their glucuronide conjugates.


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