What is the role of meconium analysis 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

Meconium analysis is currently considered the best method for detecting drug exposure in pregnancy. It provides a wider window of detection of gestational exposure, presumably as remote as the second trimester, when drugs begin to accumulate in meconium (by direct deposition from the biliary tree or when the fetus ingests amniotic fluid).

Meconium analysis is reliable for detecting opioid and cocaine exposure after the first trimester and can be used to detect a range of other illicit and prescribed medications.

However, meconium can be contaminated by infant urine, although only cocaine or opiate use within approximately 72 hours of birth is reflected. Thus, false-positive results occur if meconium is contaminated with urine, reflecting antepartum and perinatal exposure. Theoretically, lidocaine can cause a positive result, but a large amount is required.

When a meconium sample is stored at room temperature, it decreases cocaine and cannabinoid levels by 25% per day.

A study comparing umbilical cord tissue and meconium for the confirmation of in utero illicit drug exposure revealed different sensitivities of drug detection in both samples. [49] Meconium provided greater sensitivity over cord tissue, which led the study author to conclude that meconium is likely to remain the specimen of choice when sensitivity is of the greatest importance. [49]


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