Our lab recently used some nifty sleuthing to discover that soaps used in our newborn nursery were generating false positive THC urine drug screening results. Newborn drug testing has far-reaching impacts not only in healthcare, but also in the legal domain. Prenatal drug exposure is considered child abuse in several states and triggers involvement by child protective services. It is therefore imperative that urine and meconium testing at birth are both reliable and accurate.

A key factor precipitating our study was a revised screening protocol that increased the number of ordered drug screens for tetrahydrocannabinol-delta 9-carboxylic acid (THC) by the nursery. This revised protocol was implemented based on the latest recommendations for newborn drug screening. Over the course of events we learned the importance of monitoring the “total testing process.”

The story unfolded when the Newborn Nursery called the clinical lab with questions about an increase in positive THC screens from their unit. Additionally, they were concerned that in some cases meconium results did not match urine results. Reviewing the ordering history of the unit, we found the total number of tests ordered had tripled and they had seen an appropriate increase in positive tests based on historical data. We did discover however, that none of the positive samples had undergone confirmatory testing from the unit. When several samples were sent for confirmation and came back negative we became concerned and suspicious for an interferrant that was being introduced during collection.

This led to a meeting with the nurses and other key clinical staff to discuss how the samples were collected and what happens between delivery and collection of urine samples. The conversations revealed “considerable variation” between nursing staff in how the newborns were cleansed and how the samples were collected. Some nurses put cotton balls or gauze within the disposable diapers; others used collection devices, while others turned diapers inside-out.

We examined all nursery-specific products that could potentially come in contact with urine samples thus impact testing: cotton balls, collection containers, dyes present in the outer portion of the diapers. After much investigation we finally zeroed in on the baby wash as the culprit.  Addition of these soaps to drug-free urine resulted in a dose dependent response in THC assays from multiple manufacturers. We purchased other soaps at the local pharmacy to find similar results. Further evaluation of individual chemicals in the soaps with the THC immunoassay identified multiple surfactants that triggered a response.

Our findings drive home the point that confirmation by more sophisticated methods such as mass spectrometry should be considered before moving ahead with interventions such as child social services or child abuse allegations, which may be false. This has also highlighted the importance of constant re-evaluation of pre-analytical issues that may be unique to certain populations as well as the need for collaboration between multiple departments to solve problems. Once the results were published it was picked up by both local and national media outlets and it has been interesting to watch the information disseminate across the web.​