Soaps used to wash babies after birth can cause them to test positive for marijuana, a new study has found.
Researchers from the University of North Carolina (UNC) made the surprising discovery after nurses at a local hospital asked them to investigate an increase in the number of newborns testing positive for marijuana.
The researchers collected urine samples from babies washed with common baby soaps and found they tested positive for tetrahydrocannabinol (THC), the active ingredient in marijuana.
Catherine Hammett-Stabler, a professor of pathology and laboratory medicine at UNC, said some residual soap on the baby’s skin must be washed into the urine sample, resulting in a positive test.
She says parents need not fret that their baby will get "high" the test only needed a miniscule 0.1 millilitres to come up positive.
"It's not marijuana in any way, shape or form," she says.
The findings are important because social services usually get involved if tests indicate a baby has been exposed to marijuana, and parents can be accused of child abuse.
"Our findings in this study drive home the point that confirmation by more sophisticated methods should be considered before moving ahead with interventions such as child social services or child abuse allegations, which may be false," said co-author Carl J. Seashore, associate professor of pediatrics at UNC.
"We wrote this paper to inform care providers and laboratory medicine people in hospitals that this issue is out there and that positive urine screens for THC need to be confirmed."
The researchers say the positive test results could be due to compounds in the soap that have a similar structure to THC, or that the soap chemicals alter the way the test operates.
The study was published in the June issue of the journal Clinical Biochemistry.