False Positive THC in Infants

Surprising source of positive medical lab test results was discovered by a special team including pathologists, medical technologists, nurses, and physicians

Some innovative sleuthing by clinical laboratory professionals at University of North Carolina School of Medicine (UNCSM) hospitals has helped solve a marijuana mystery involving neonatal screenings. An unexpected spike in “false positive” cannabis exposure screening results in newborns at the facilities triggered a study by UNCSM scientists.

According to a story in MedCity News, in July 2011, the UNCSM clinical laboratories received a call from nurses in the neonatal nursery. They had noticed an increase in positive results in screenings for tetrahydrocannabinol-delta 9-carboxylic acid (THC). THC is the principal psychoactive component of the cannabis plant.

Five months earlier, in February 2011, a revised screening protocol had been instituted at UNC Hospitals, consistent with the latest recommendations for newborn drug screening. The revised protocol increased the use of the urine immunoassay for identifying THC in newborns, the story stated.

Urine samples were testing positive for THC. However, subsequent testing of meconium samples from the same newborns tested as negative. Neither the maternal nor infant drug histories showed agents that could alter screening results. Something other than marijuana use was causing the false positives.

“Mixtures of drug-free urine with various commercial products and materials that commonly contact newborns in our nursery were prepared and tested using the immunoassay screening methods in our laboratory,” the authors wrote in the abstract of the study, published in the June issue of Clinical Biochemistry.

The team started sending newer samples that tested positive for THC to a reference laboratory for confirmation using more sophisticated techniques, such as mass spectrometry, a story published at HealthCanal.com reported.

“The results did not match up with the original screens; they were not confirmed,” stated Catherine A. Hammett-Stabler, Ph.D., Professor of Pathology and Laboratory Medicine and Executive Director of the Core Laboratory of the William W. McLendon Clinical Laboratories at UNC Hospitals. He was the pathologist who led the study.

Neonatal screenings at University of North Carolina Medical School newborn nurseries experienced a spike in positive in utero marijuana exposure screenings. An investigation conducted by a team that included pathologists, clinical laboratory scientists, physicians, nurses, and others used more sensitive methods of clinical laboratory testing to determine that the source of the positive marijuana test results was several different brands of baby wash products in use in the hospital’s nursery.

Weeding out possible culprits, the researchers eliminated cotton balls, collection containers, and possible dyes in the outer portion of diapers. Then they began testing the newborn nurseries’ commercially available baby washes.

Testing showed that four out of seven commercial baby soaps tested caused a “false positive” in cannabis exposure screening results. They identified polyquaternium-11 and cocamidopropyl betaine as the chemicals potentially triggering the false positives, a story published at medicalxpress.com stated.

“Structurally, these things don’t look like marijuana metabolites, but clearly they are being recognized by the antibodies used in the immunoassay,” Hammett-Stabler said in a statement, according to MedCity News. “And when testing those reagents in increasing concentrations, we did see a positive response, albeit really low, just over the point of positive.”

Citing important health and legal ramifications, the study authors stressed that accuracy of the results cannot be undervalued. “Our findings in this study 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,” stated study co-author Carl J. Seashore, M.D., Associate Professor of Pediatrics at UNC and Director of the Newborn Nursery.

Clinical laboratory managers and pathology groups should take notice of this potential source of false positive screening results. They may want to consider a more sensitive method of confirmation before initiating interventions in similar situations. It is also a reminder of the need for vigilance against sources of error that may derive beyond the walls of the clinical laboratory.

Source: http://www.darkdaily.com