Baby Wash Linked to False-Positive In Utero Marijuana Exposure

Deborah Brauser

June 22, 2012

June 22, 2012 — Baby wash products, including soaps and shampoos, may trigger false-positive screening results for in utero exposure to marijuana in newborns, new research suggests.

Concerned with the increased rates of newborns in their nursery who were testing false-positive for tetrahydrocannabinol (THC) acid, investigators from the University of North Carolina (UNC) sought to track down the cause of these results.

Baby wipes, gauze, cotton balls, diapers, and urine collection bags incubated with drug-free urine samples showed no reactivity with the THC screening assay. However, the addition of Head-to-Toe Foaming Baby Wash (Johnson & Johnson) showed a dose-dependent response "exceeding the threshold for a positive screening."

Although 6 of the 7 other commercial baby soap products tested showed some level of reactivity with the THC assay, only 4 actually caused positive screening results.

"We were extremely surprised by these findings," principal investigator Catherine Hammett-Stabler, PhD, professor of pathology and laboratory medicine at UNC, in Chapel Hill, and director of the Core Laboratory of the McLendon Clinical Laboratories at UNC Hospitals, told Medscape Medical News.

Dr. Catherine Hammett-Stabler and Dr. Steven Cotton

"We originally thought there would be a simple explanation — either that there had been a real drug exposure or there was just a real difference between the measures of meconium and of urine. But when we discovered they really were negative screens, we very surprised to find it was due to the soap," said Dr. Hammett-Stabler.

"I mean, soap? Past literature has shown that's supposed to cause false-negatives."

The investigators note that false-positive screenings can result in the involvement of social services or in false child abuse allegations.

"Given these consequences, it is important for laboratories and providers to be aware of this potential source for false...results and to consider confirmation before initiating interventions," they write.

The study is published in the June issue of Clinical Biochemistry.

Hot Button Issue

"Identification of newborns exposed to drugs of abuse in utero is a challenging and even controversial process," write the researchers.

"Nevertheless, accurate assessment of drug exposure in this population is critical to ensure both protection of the child and support for the family," they add.

The investigators note that most clinical laboratories now test urine and/or meconium in newborns to measure drug exposure.

In July 2011, discussions between UNC staff and researchers arose because of an increase in the number of positive urine drug screens that did not coincide with positive meconium results.

It was found that the nursing staff varied in their cleansing procedures for newborns before and during sample collections.

"Therefore, we sought to examine all nursery-specific products that could potentially come in contact with newborn urine samples to determine any potential effect on THC screening," report the investigators.

Results showed that the addition of the Head-to-Toe Baby Wash "yielded a response above the limit of detection, but below the cut-off, at 10.2 μg/L. Subsequent evaluation of increasing amounts (0.02 - 0.08 mL)...revealed a dose dependent increase with the results exceeding the threshold for a positive screening result when less than 0.1 mL of wash was added to the samples," write the researchers.

The following 6 commercial baby soap products also showed some level of reactivity with the THC assay:

  • Johnson & Johnson's Bedtime Bath

  • CVS Night-Time Baby Bath

  • CVS Baby Shampoo

  • Aveeno Soothing Relief Creamy Wash (Johnson & Johnson)

  • Aveeno Wash Shampoo

  • Baby Magic: Hair and Body Wash (Naterra Inc.)

Only hospital foaming hand soap showed no reactivity.

Of the 6 products that did show reactivity, 4 caused assay interference strong enough to yield a positive screening result (Night-Time Baby Bath, Bedtime Bath, and both Aveeno products).

Subsequent testing found that the components from the products associated with positive assay reactivity included polyquaternium 11; cocamidopropyl betaine; and a combination of PEG 80, sorbitan laurate, and cocamidopropyl betaine.

Need for Confirmatory Testing

"In the drug-testing world, soap or detergent is thought to be a way of thwarting detection of drug use, and can often result in false-negative screening results. So our finding that use of these soaps resulted in false-positive results was very surprising," said Dr. Hammett-Stabler.

She noted that the findings did not show that any of the products contain marijuana, nor are the investigators suggesting that hospital nurseries stop using the washes.

Instead, she suggests that newborns be given these tests before being bathed and that the babies should be carefully rinsed off before being tested.

The investigators add that the study demonstrates "the need for active involvement in the 'total testing process,' as sources of error are not confined to the laboratory walls."

They suggest that confirmation tests with more sophisticated methods, such as mass spectrometry, should be considered before involving social services or other agencies.

"If you're going to make decisions that could have a long-term legal impact, you should look at having results confirmed. It will often take anywhere from 1 to 5 days to get those results back. But if it's a legal-type of action, it's prudent to do that," said Dr. Hammett-Stabler.

The study authors have disclosed no relevant financial relationships.

Clin Biochem. 2012;45:605-609. Abstract

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