The ability of physicians to predict electrolyte deficiency from the ECG

The ECG is considered to be a fairly accurate reflection of a patient's electrolyte status. Two full-time academic emergency physicians, each board certified in two specialties, interpreted the ECGs of 97 consecutive alcoholic patients presenting to the emergency department. Serum potassium, calcium, and magnesium values were obtained on all patients within one hour of ECG performance. The physicians attempted to predict abnormalities of serum electrolytes from the ECG tracing alone when blinded to all laboratory values, the clinical situation, and each other's readings. The combined results of both readers yielded a sensitivity of .74 and a specificity of only .29. The positive predictive value of the ECG in predicting electrolyte deficiency was .41 and the negative predictive value was .63. Electrolyte disturbances cannot be accurately predicted from an ECG even in high-risk patients. Serum electrolyte determinations remain the most effective method of screening for these deficiencies.