Rapid bedside assessment of serum caffeine concentrations using an immunochromatographic screening kit: evaluation of analytical and diagnostic performance in acute caffeine poisoning

INTRODUCTION: Severe caffeine poisoning can be life-threatening, and rapid identification of toxic or potentially lethal serum caffeine concentrations may provide additional information. However, rapid quantitative analysis using advanced techniques is often unavailable in emergency settings. The Multi-Drug Rapid Test Cassette (CAF10000 + CAF50000), is an instrument-free immunochromatographic assay for the detection of caffeine. This study evaluated the diagnostic performance of the Multi-Drug Rapid Test Cassette kit in patients with acute caffeine poisoning. METHODS: In this prospective single-centre study, 26 patients with suspected acute caffeine poisoning provided 40 serum samples between 2018 and 2025. The Multi-Drug Rapid Test Cassette kit reaction patterns were compared with serum caffeine concentrations measured by liquid chromatography-tandem mass spectrometry. Additional analysis included the evaluation of cross-reactivity with caffeine metabolites and commonly co-ingested drugs, as well as assessment of serum caffeine stability under different storage conditions. RESULTS: Using undiluted serum, the Multi-Drug Rapid Test Cassette kit reaction patterns were generally consistent with classification into three predefined ranges: <10, 10-50 and >50 µg/mL. At higher concentrations, both test strips remained positive, limiting further discrimination. When estimated undiluted concentrations exceeded approximately 80 µg/mL, both test strips remained positive even after fivefold dilution. This observation was exploratory. No cross-reactivity was observed with caffeine metabolites or commonly co-ingested drugs. Serum caffeine concentrations remained stable under all tested storage conditions. DISCUSSION: The Multi-Drug Rapid Test Cassette kit demonstrated the ability to categorize serum caffeine concentrations into predefined ranges and showed no interference from metabolites or co-ingested drugs, suggesting good analytical specificity. CONCLUSIONS: The Multi-Drug Rapid Test Cassette kit was able to classify serum caffeine concentrations into predefined ranges without analytical instrumentation. Further studies are warranted to evaluate the clinical relevance of these analytical findings.