# Immunalysis tapentadol assay reformulation resolves tramadol interference

## TL;DR

A new reformulated test kit for tapentadol reduces false positives caused by tramadol interference, improving drug screening accuracy.

## Contribution

A reformulated assay kit is introduced to resolve tramadol cross-reactivity in tapentadol urine screening.

## Key findings

- 61% of false-positive tapentadol samples contained tramadol below the reported cross-reactivity threshold.
- The reformulated kit eliminated false positives and aligned with LC–MS/MS confirmation.
- False-positive rates significantly decreased after implementing the new kit in routine testing.

## Abstract

This study evaluated the performance of the Immunalysis Tapentadol 343 Urine Enzyme Immunoassay (EIA) screening kit, focusing on the prevalence of false-positive results due to cross-reactivity with tramadol. Tapentadol is a dual-action analgesic, modulating μ-opioid receptors and inhibiting norepinephrine reuptake, while tramadol, a structurally related compound, is a weak μ-opioid receptor agonist and norepinephrine/serotonin reuptake inhibitor. Cross-reactivity between these compounds can complicate urine drug screening results for adherence monitoring in chronic pain management. A total of 28 samples initially produced false-positive results for tapentadol BNl using the Immunalysis Tapentadol 343 Urine EIA screening kit. Liquid chromatography–tandem mass spectrometry (LC–MS/MS) was used to confirm the absence of tapentadol. Of the false-positive samples, 61% contained tramadol at concentrations below the manufacturer-reported cross-reactivity threshold of 60 000 ng/mL, indicating assay limitations in specificity. To address this issue, a newly reformulated Immunalysis Tapentadol 343UR Urine HEIA kit was evaluated for tramadol cross-reactivity. Upon retesting the 28 false-positive samples with the reformulated kit, no false positives were detected, with results consistent with LC–MS/MS confirmation. The rate of false-positive tapentadol screens in urine has substantially reduced since the implementation of the new tapentadol kit in routine testing. These findings demonstrate the importance of assay verification to assess cross-reactivity, particularly for structurally related compounds. The reformulated Immunalysis Tapentadol 343UR kit shows improved specificity, reducing false-positive rates and enhancing the accuracy of tapentadol detection in clinical and forensic toxicology applications.