The appropriate use of serum digoxin assay.

The serum digoxin assay has become a popular laboratory test. However, its use is only appropriate if new information is gleaned which ultimately influences the physician's decision making. There are pitfalls inherent in the test if the technique is not standardized, or if the sample is taken randomly rather than at least 12 hours after the last dose of the drug. Moreover, therapeutic levels derived from adult patients in sinus rhythm cannot be applied to infants, nor to patients with atrial fibrillation.The development and use of the serum digoxin test has broadened awareness of digitalis pharmacokinetics. Its clinical implementation has occurred concurrently with other advancements in digitalis pharmacology such as bioavailability studies and the concept of low loading dosage. Together, all these factors have had an educational effect on physicians and lowered the frequency of digitalis toxicity.The physician must consider the complete patient in his total clinical milieu, and not treat only a laboratory result, i.e. the serum digoxin level.