Seven different digoxin immunoassay kits compared with respect to interference by a digoxin-like immunoreactive substance in serum from premature and full-term infants

Abstract

Seven different digoxin immunoassay kits showed cross reactivity with an endogenous digoxin-like immunoreactive substance consistently present in serum of neonates, whether premature or full-term. The degree of interference, in decreasing order was: NML > New England Nuclear > BioRad > Clinical Assays > Beckton Dickinson > Serono > Syva (EMIT). More recently purchased NML kits showed less differences in antibody. A single baseline determination of the substance before digoxin is administered inadequately compensates for this interference, because the interferent concentrations can differ from day to day, with evidence that it may be most concentrated on the fourth to sixth postnatal day. Its concentration in the serum of neonates is unrelated to the concentration of dehydroepiandrostenedione sulfate, an indicator of fetal adrenal-cortical activity.