This study addresses the challenge of accurately assessing diazinon exposure in suspected self-poisoning cases. We evaluated butyrylcholinesterase (BChE) levels using a point-of-care (POCT) whole blood assay (adapted Ellman method) and compared it with the standard plasma Enzyme Multiplied Immunoassay Technique (EMIT). Diazinon exposure in four patients was confirmed using a validated gas chromatography–tandem mass spectrometry (GC-MS/MS) method with multiple reaction monitoring (MRM). A strong positive correlation was observed between POCT and EMIT BChE activity (r = 0.9638, p < 0.0001), indicating general agreement in BChE trends. However, Bland–Altman analysis revealed discrepancies in absolute BChE values. Notably, admission diazinon concentrations (GC-MS/MS) were significantly negatively correlated with BChE activity measured by both POCT (r = −0.9333, p = 0.0205) and EMIT (r = −0.9302, p = 0.0219). The POCT assay offers rapid, preliminary BChE assessments in suspected diazinon intoxication, useful in emergency settings. However, due to observed discrepancies, confirmatory testing with EMIT or GC-MS/MS is recommended for accurate quantification. This research highlights the critical need for robust confirmatory methods, such as GC-MS/MS, to validate rapid assays and improve the accuracy of diazinon intoxication detection.

Background: Accurate and prompt assessment of malathion intoxication severity remains a significant clinical challenge, often hampered by reliance on single diagnostic markers. This exploratory case series investigated the combined utility of rapid butyrylcholinesterase (BChE) activity measurements and gas chromatography-tandem mass spectrometry (GC-MS/MS) for quantifying urinary malathion to enhance diagnostic precision. Methods: We investigated three independent patients admitted with acute malathion intoxication. BChE activity was measured using both a point-of-care (POCT) device and a laboratory-based enzyme-multiplied immunoassay technique (EMIT). Urinary malathion was quantified using a validated GC-MS/MS method. Results: Malathion exposure was confirmed in all patients via urinary analysis. Strong per-case positive correlations (r ranging from 0.905 to 0.996) were observed between the two BChE measurement methods, though Bland-Altman analysis revealed noteworthy discrepancies (mean bias of 10%, limits of agreement ranging from −20% to 40%). Critically, statistically significant inverse correlations ( p < 0.05) were identified between urinary malathion concentrations and both BChE activity measurements, underscoring the dynamic relationship between exposure and enzymatic inhibition. Conclusion: These findings, derived from a small, exploratory case series, suggest the importance of an integrated diagnostic approach for malathion intoxication. This combined strategy may support improved assessment of severity and prognosis in individual cases, offering insights into the pesticide’s systemic impact and elimination kinetics, especially when exposure details are unclear. While rapid BChE tests are valuable for initial screening, their interpretation should occur within this multi-marker framework. The generalizability of these findings is limited by the small sample size, and no formal power calculation was performed.