Falsely Increased Digoxin Concentrations in Samples from Neonates and Infants

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Abstract
Different immunoassay kits (8) were studied to confirm the presence of a digoxin-like immunoreactive substance. The kits were evaluated using serum from newborns and infants who were not receiving digoxin. The relationship of this digoxin-like immunoreactive substance to substances present in unusual concentrations in newborn sera was investigated. These substances included fatty acids, cholesterol, triglycerides, bilirubin, protein and albumin. No relationship could be established. Since serum steroid concentrations are increased in the newborn and since digoxin is essentially a steroid derivative, steroids were examined separately and collectively to see whether they mimicked the immunoreactivity of digoxin. Pooled steroids did indeed mimic digoxin and might be implicated as the immunoreactive substances.