Evaluation of the interference of lamotrigine on the analysis of synthetic cannabinoids in urine by the immunoassay method

We aimed to evaluate the interference of lamotrigine (LMG) on the synthetic cannabinoids metabolite-K2/1 (SCm/K1) urine test by Homogeneous Enzyme Immunoassay (Immune-SCm/K1). This study consists of two parts: case-control and interference effect research. In the case-control study, two groups using LMG and a non-use of LMG were formed, all of them non-SC users. In the interference effect research, four groups were formed by adding either a LMG stock solution or a LMG user's urine to a SCm/K1 negative urine, and Immune-SCm/K1 test calibrators and quality control (QC) materials. Immune-SCm/K1, SCm/K1 by LC/MS-MS and LMG tests were performed on all samples in the study. The case-control study was performed on a total of 55 participants (mean age 39.76 ± 9.84 years). Both groups were statistically insignificant in terms of age and gender. Urine LMG levels were 5.71 ± 10.61 mg/L in the LMG group and <0.30 mg/L in the control group. Immune-SCm/K1 results were 35.84 ± 7.62 ng/mL in the LMG group, <3.00 ng/mL in the control group and the LC/MS-SCm/K1 urine test of both groups were found to be 'NEGATIVE'. Results were interpreted as a cross-reaction in the interference study and a statistically significant relationship was found between LMG levels and Immune-SCm/K1 levels in the SCm/K1 negative samples (groups 1 and 2) (R² = 0.9341 and R² = 0.9941, respectively; p < .001). LMG interference was observed in SCm/K1 positive samples ranging from -6.17 to 714.77%. LMG in the specimen interferes with the Immune-SCm/K1 screening test and causes false positivities.