13-Year-Old Girl With Recurrent, Episodic, Persistent Vomiting: Out of the Pot and Into the Fire

Recently, Felton et al. reported a case study for cyclic vomiting syndrome that included a urine drug immunoassay test result positive for cannabinoids. The authors concluded that the result was a false positive, potentially due to the use of pantoprazole. Further, a major conclusion of the article is that false positives (FP) for cannabinoids due to use of proton pump inhibitors (PPIs) such as pantoprazole should be considered when urine drug testing is performed for patients being treated with PPIs.

Unfortunately, this published case report includes cited reports that never fully tested the potential for PPIs to cause FP immunoassay results for cannabinoids. The authors themselves indicate that the mechanism for FP "is scant, with all references referring to the pantoprazole package insert that describes pre-Food and Drug Administration approval data." Further, there is peer-reviewed data indicating hand soap as one possible explanation for observed false positives with cannabinoid immunoassays in the pediatric setting(1). In addition, there is evidence (cited by Felton et al.) that metabolism of cannabinoids may be unique in the pediatric population and FP immunoassay results for cannabinoids may be false negative confirmation results due to the use of confirmation methods validated in the adult population(2).

Felton et al. fail to describe the immunoassay used (reagent vendor, platform), performance characteristics (cutoff, quality control) or details regarding the GC-MS assay (sample preparation, cutoff, LOQ, etc.). Further, there is no indication if the GC-MS assay was a true negative or if there was evidence of THC below the reporting limit of the assay. Every clinical laboratory determines the cutoffs used for reporting urine drug testing results and the ranges can vary significantly. In our own internal studies, addition of pantoprazole directly to negative urine as well as collection of urine from patients taking pantoprazole or alternative PPIs yielded no FP cannabinoid results using the SIEMENS EMIT II Plus cannabinoids assay on a Beckman analyzer. While it has yet to be conclusively determined whether PPIs may cause cannabinoid FPs, the case report by Felton et al. does little to further our understanding in this already complicated area of testing.

Defining truth in the field of urine drug testing is challenging for the physician and laboratory, and publication of anecdotal observations further confuses the situation when key details are not included. While case reports are often of value, it is important that well controlled data accompany the reports or means to collect such data are attempted. In the above situation, had the authors included a pre-treatment urine collection their argument could have been supported. As it stands, this case report inappropriately perpetuates the idea that PPIs are at fault for unexpected cannabinoid positive immunoassays providing a mechanism for patients to plant a seed of doubt in the minds of treating physicians.

1. Mays DA, McCarthy TJ. Letter to the Editor regarding a report about the potential for commonly used baby cleansers to interfere with cannabinoid (THC) immunoassays. Clin Biochem. 2012;45(15):1266; author reply 7.
2. Barakauskas VE, Davis R, Krasowski MD, McMillin GA. Unresolved Discrepancies between Cannabinoid Test Results for Infant Urine. Clinical Chemistry. 2012;58(9):1364-7.

Conflict of Interest:

None declared