Digoxin-like substance in term pregnancy, newborns, and in renal failure

Digoxin-like substance (DLS) is detected in term mothers, newborns, and in patients with renal failure. The authors made ''digoxin'' measurements in such patients using three RIA kits (Nuclear Medical Laboratories (N), Clinical Assay (C), Corning MAGIC (M)). We first defined zero concentration and demonstrated quantitative recoveries. We estimated DLS in 28 at-term mothers, cord blood of 23 unrelated newborns, 25 infants 2-3d of age and sequentially in 10 additional mothers and their infants using C only; and in 35 renal failure patients pre- and post-dialysis, 12 of whom were receiving digoxin. At-term mother DLS (μg/L digoxin) was 0-0.19 (N), 0.09-0.24 (C), 0.07-0.24 (M); cord blood DLS was 0.35-0.75 (N), 0.46-0.90 (C), 0.42-0.90 (M); infant DLS was 0.5-1.1 (N), 0.28-0.98 (C). DLS was detected in mothers at term but not 24h post delivery. Cord levels fell in 8 of 10 infants in 48h. Dilutions of cord blood yielded similar results by N, nonlinear decreases by C and more nearly parallel decreases by M. DLS in renal patients not receiving digoxin was 0.04-.41 (N), 0.01-0.34 (C), 0.03-0.40 (M). Post-dialysis levels by N were lower than pre-dialysis, but higher by C and M. In patients receiving digoin, pre- and post-dialysis levels were similar except for digoxin > 1.0 μg/L, which fell. Dilutions yielded similar results by N but nonparallel results by M. DLS assay effects must be characterized for these patient populations in order to avoid errors in digoxin estimation