Case Definition: Digitalis

Clinical description

Signs and symptoms of acute digitalis (digoxin or digitoxin) poisoning by ingestion include primarily gastrointestinal effects (nausea and vomiting), hyperkalemia, and cardiovascular effects (bradydysrhythmias [heart rate <60 or atrioventricular block] or tachydysrhythmias [ventricular tachycardia/fibrillation or atrial tachycardia with 2:1 block]) (1-4).

Laboratory criteria for diagnosis

• Biologic: A case in which digitalis in serum samples is detected, as determined by a commercial laboratory.
  • Therapeutic levels of digoxin typically range from 0.5 to 2.0 ng/mL. (3-4)
    • Multiple determinants exist for digoxin poisoning and serum digoxin concentrations overlap between symptomatic and asymptomatic patients. Therefore, diagnosis of clinical poisoning should not necessarily be made solely on the basis of laboratory testing results compared with the therapeutic range. The serum digoxin concentration should be correlated with the clinical findings of the patient and the details of the exposure (e.g., time elapsed since exposure, etc…).
    • Serum concentrations might be detectable after an exposure to plant-derived cardiac glycosides, some of which can cross-react with the various hospital laboratory assays used. Of note is that, these values may underestimate serum concentrations due to imperfect cross-reactivity. In addition, false-positives might be noted for pregnant women and for patients with liver and renal disease (3).

- OR-

• Environmental: Detection of digitalis in environmental samples. (5-8)

Case classification

• Suspected: A case in which a potentially exposed person is being evaluated by health-care workers or public health officials for poisoning by a particular chemical agent, but no specific credible threat exists.
• Probable: A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for digitalis exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
• Confirmed: A clinically compatible case in which laboratory tests have confirmed exposure.

The case can be confirmed if laboratory testing was not performed because either a predominant amount of clinical and nonspecific laboratory evidence of a particular chemical was present or the etiology of the agent is known with 100% certainty.

Additional resources

1. Kanji S, Maclean RD. Cardiac glycoside toxicity: More than 200 years and counting. Crit Care Clin 2012; 28:527-35.
2. Ma G, Brady WJ, Pollack M, Chan TC. Electrocardiographic manifestations: Digitalis toxicity. J Emerg Med 2001; 20(2):145-52.
3. Hack JB. Cardioactive steroids. In: Nelson LS, Lewin NA, Howland MA, Hoffman RS, Goldfrank LR, Flomenbaum NE, eds. Goldfrank's Toxicologic Emergencies. 9th ed. New York, NY: McGraw-Hill; 2011: 936-45.
4. Benowitz NL. Cardiac glycosides. In: Olsen KR, Anderson IB, Benowitz NL, et al., eds. Poisoning and drug overdose. 4th ed. New York, NY: McGraw-Hill; 2004:155-7.
5. NIOSH. NIOSH manual of analytical methods [online]. 2003. [cited 2013 Apr 5]. Available from URL: http://www.cdc.gov/niosh/docs/2003-154/.
6. OSHA. Sampling and analytical methods [online]. 2010. [cited 2013 Apr 5]. Available from URL: http://www.osha.gov/dts/sltc/methods/index.html.
7. FDA. Food: Laboratory methods [online]. 2013. [cited 2013 Apr 5]. Available from URL: http://www.fda.gov/Food/FoodScienceResearch/LaboratoryMethods/default.htm.
8. EPA. Selected analytical methods: chemical methods query [online]. 2013. [cited 2013 Apr 5]. Available from URL: http://www.epa.gov/sam/searchchem.htm.