Serum digoxin‐like immunoreactive factor in children and its relation to sodium metabolism

Serum digoxin-like immunoreactive factor (DLIF), an endogenous substance that cross-reacts with antidigoxin antibodies, was assessed (fluorescence polarization immunoassay) in children (n = 134) aged 5-16 y, who had never been treated with cardiac glycosides. DLIF was found in 50% of serum samples at a mean concentration of 0.16 +/- 0.06 ng/ml (range 0.03-0.35 ng/ml). Although the study population as a whole was apparently homogeneous with regard to serum sodium content, and none had clinical signs of sodium imbalance, children with DLIF showed significantly lower natraemia (p = 0.0002), higher urinary concentration (p = 0.001) and fractional excretion (p = 0.001) of sodium, and increased systolic blood pressure (p = 0.009) compared with children without DLIF. Inverse correlations were found between DLIF concentration and serum sodium (p < 0.01), urine sodium content (p < 0.001), 24-h sodium excretion (p < 0.001), systolic (p < 0.001) and diastolic (p < 0.01) blood pressure. These findings suggest that sodium handling is different in children with and without DLIF, since this material seems to be released preferably in subjects who show a trend towards negative sodium balance. Such an association suggests that DLIF may be a physiologically relevant material involved in sodium homeostasis.