Clinical evaluation of a new digitoxin enzyme-immunoassay

A solid-phase enzyme-immunoassay for the determination of the digitoxin concentration in human serum (Enzymun-Test Digitoxin) was developed, and subsequently evaluated in seven laboratories. The test is based on the competition principle. Polystyrene tubes coated with anti-digitoxin antibodies (from sheep) were used as the solid phase. In the concentration range 10-40 micrograms/l, the coefficient of variation for the majority of laboratories was between 2 and 7%. The day-to-day precision only slightly differed from the within-run precision. The measuring range was between 4 and 60 micrograms/l. Enzymun-Test Digitoxin showed good agreement with three known methods for digitoxin determination. No influence on the values was observed in lipaemic, uraemic and icteric samples, dysproteinaemia sera and in the presence of various digoxin derivatives. The new enzyme-immunoassay permits the practical and reliable determination of serum digitoxin and is suited for use in routine analysis.