Serum potassium level as a biomarker for acute caffeine poisoning.

Aim: Acute caffeine poisoning presents with hypokalemia, although a relationship between potassium levels and blood concentrations of caffeine has not been established. A correlation between serum potassium level and blood caffeine concentration could establish serum potassium as a simple marker to assess caffeine toxicity in patients with acute toxicity. We investigated whether serum potassium, a symptom of acute caffeine poisoning, could be a parameter correlated with blood caffeine levels.

Methods: We enrolled 85 patients treated for acute caffeine poisoning between January 2012 and March 2019 with blood caffeine levels measured after an overdose of a caffeine-containing over-the-counter drug and for whom serum potassium levels were available. We examined the correlation between serum potassium and blood caffeine concentration. A receiver operating characteristic curve was created with serum potassium values to stratify participants into two groups by blood caffeine concentrations: <20 or ≥20 mg/L (toxic dose) and <80 or ≥80 mg/L (lethal dose). The lethal cut-off value was calculated.

Results: The correlation coefficient between serum potassium level and blood caffeine concentration was -0.612 (  = 0.374), indicating a negative correlation. The areas under the curve at blood caffeine concentrations of 20 mg/L (toxic dose) and 80 mg/L (lethal dose) and serum potassium levels were 0.716 and 0.888 (sensitivity, 0.829 and 0.919; specificity, 0.568 and 0.818; cut-off, 3.3 mEq/L and 2.9 mEq/L), respectively.

Conclusion: Serum potassium levels are associated with blood caffeine concentrations; K of 3.3 mEq/L and 2.9 mEq/L indicate acute caffeine poisoning in the toxic and lethal dose, respectively.