[Rheumatoid factors and immunoglobulins as interfering factors in a heterogeneous enzyme immunoassay]

Enzymun-Test Digoxin was used to analyse model samples. The matrix of the model samples consisted of either phosphate-buffered 0.15 mol/l sodium chloride solution pH 7.2 with addition of albumin or immunoglobulins, or of various ratios of albumin and immunoglobulins, most of which had been characterized immunoelectrophoretically. Increasing amounts of albumin or immunoglobulins in the model samples caused a simulated increase in the measured amount of digoxin. Apparent digoxin values also showed corresponding false increases when immunoglobulins of certain specificities were increased in the model samples, even when total protein was kept constant.