NACB - Scientific Shorts
NACB - Scientific Shorts (formerly NACB Blog)
By Steve Cotten, PhD and Catherine Hammett-Stabler, PhD

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.​ 


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Posted by Marc McCain
On 7/17/2012

It has been my experience that CPS or whatever it is called in each locaility is far too quick to act in these situations which can and has caused babies to be improperly separated from their family at a very critical time. This has been due to the failure to have a PROPER confirmation performed. In my previous position my departments (Clinical and Forensic Toxicology) were responsible for analyzing urine collected from babies at several hospitals. We found a very high incidence of "positive" screens by EMIT and FPIA but a very low correlation when analysis by GC/MS was performed. As a result it became part of the protocol to not release results until the confirmation was performed. Several times I had battles with CPS since a quick screen had been performed in the hopsital and either the baby had already been removed from the mother's access or CPS wanted to remove access. While I do not have exact numbers I do know that over 95% of the samples that screened positive failed to confirm, even at the limit of detection of the assay (2.0 ng/mL). The take away here is basically the same as the author's last paragraph except I would replace should with must. The final sentance should read "Our findings drive home the point that confirmation by more sophisticated methods such as mass spectrometry must be performed before moving ahead with interventions......"

Posted by Richard Struempler
On 7/16/2012

It is unfortunate that the clinical laboratory in this case is just now learning a painful lesson that was learned almost 30 years ago in the employment drug testing arena. If results from a drug test are to be used for something other than a clinical evaluation and may have adverse legal or adminitrative implications then the inital positive test result must be confirmed by a more analytically specific method (GC/MS, LC/MS/MS/MS). To practice otherwise places the patient in jeopardy, not to mention the potential legal reprocussions against the medical community allowing testing like this to occur. No one with any experience with issues regarding forensic drug testing and possible false-positive results from an immunoassay test method would be surprised at these findings.