Digoxin-like immunoreactive substance in serum of preterm and full-term neonates.

A significant serum level of digoxin-like immunoreactive substance (DLIS) (greater than or equal to 0.5 ng/ml) has been found in healthy full-term neonates, in prematurely born neonates as well as in full-term but small for gestational age neonates. Neither the babies nor their mothers had received digoxin therapy. On the first day of life, the incidence of serum levels of DLIS greater than or equal to 0.5 ng/ml in the three groups of neonates were respectively 64% (32/50), 42% (8/19) and 77% (10/13). Longitudinal measurements in preterm and small for gestational age neonates indicate a progressive disappearance of DLIS from their serum, none of them having a significant serum level at 21 days of age. As long as the chemical structure, origin and physiological properties of DLIS remain unknown, clinicians must be cautious in interpreting the serum levels of digoxin used for therapeutical purpose in neonates.