What is the role of lab testing in the diagnosis of caffeine toxicity?

Updated: Oct 24, 2020
  • Author: David Yew, MD; Chief Editor: Michael A Miller, MD  more...
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The patient's signs and symptoms should guide the use of laboratory studies. In hemodynamically stable patients with mild symptoms who give a clear history of caffeine ingestion, no laboratory studies are indicated.

The following laboratory studies are indicated in patients with moderate-to-severe symptoms of caffeine toxicity (ie, hemodynamic instability, dysrhythmias, seizures, altered mental status).

  • A complete blood cell count (CBC) should be checked to evaluate for infection. Mild leukocytosis (11-16 × 109 L [11,000-16,000/mL]) can be present in caffeine toxicity; however, infectious processes should be excluded.

  • Serum electrolyte, glucose, blood urea nitrogen (BUN), and creatinine concentrations should be checked. Pay particular attention to potassium concentrations and the anion gap. Hypokalemia is a classic feature of caffeine overdose. An increased anion gap (resulting from lactic acidosis) and hyperglycemia are also common findings in severe toxicity.

  • Routine screening for other potentially treatable toxins (eg, acetaminophen, salicylate) is recommended. Such testing is essential if the patient ingested analgesic medications containing caffeine combined with other drugs (eg, Excedrin, Cafergot, Fiorinal or Fioricet, Midol, Anacin).

  • Measure total creatine kinase (CK) concentrations to check for rhabdomyolysis, which is occasionally associated with severe caffeine toxicity. A CK concentration greater than 5 times the upper limit of normal indicates clinically significant rhabdomyolysis. Include the CK-MB fraction and troponin level if myocardial ischemia is suspected.

  • Results of dipstick urinalysis may give a rapid indication of rhabdomyolysis, myoglobinuria, or both. Glucosuria and ketonuria are also common findings.

  • A rapid urine drug screen may help in identifying co-ingested substances. Illicit drugs, such as ecstasy or methamphetamine, often contain caffeine as a substitute or co-ingredient. Standard urine drug tests usually cannot detect ecstasy or methamphetamines.

  • Consider checking serum ethanol concentrations and osmolality in cases of unknown ingestion or suspected co-ingestion.

  • A serum pregnancy test is indicated in all women of childbearing age.

  • Thyroid studies should be considered because thyrotoxicosis can mimic caffeine toxicity.

  • Arterial blood gas analysis is indicated in patients with respiratory compromise, with altered mental status, or with a need for mechanical ventilation.

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