Michael Henderson, and Michael H. Kutner (Depts. of. Surgery ... Rypins EB, Sankary H, Wynn HJ. ... substitute, 4 h before the specimen was taken, the usual.
What is needed to make this method reliable in the presence of ascorbic acid is a different procedure for purification of the sample that preserves the preformed oxalate and eliminates the ascorbate without converting it into oxalate. The ascorbic acid must be removed, not simply left in the sample as ascorbate because, as I have observed, this inhibits the enzymatic assay and causes a negative bias.
Dlgoxin Radioimmunoassay That Does Not Detect Dlgoxin-like Substance in Serum of Newborns, Infants, or Patients with Renai Failure, Lynn Witherspoon, Stanton Shuler, Harold Neely, Robert Sonnernaker, Kristin Alyea, and Susan Gilbert (Ochsner Clinic and Alton Ochsner Medical Foundation, 1516 Jefferson Hwy., New Orleans, LA 70121) We recently
described
inaccurate
digoxin
estimates
(caused by digoxin-like substance, DLS), detected with three radioimmunoassays, in serum of near-term pregnant wom-
en, their infants, other neonates, and patients with renal failure (1). We report here a different experience with a digoxin radioimmunoassay from Diagnostic Products Corp., Los Angeles, CA (DPC). We compared apparent concentrations of digoxin in serum measured with the DPC liquid-phase second-antibody and with the NML (Nuclear Medical Laboratories, Irving, TX) assays, following the protocols without modification (except 25-zL samples were used for infants) for 43 adults receiving digoxin, 16 newborns (cord blood), and 16 patients with chronic renal failure who were not receiving digoxin. We also measured digoxin in undiluted serum from 14 infants who were receiving the drug (13 samples were also diluted twofold) by the DPC method and from 10 of these infants (seven samples were diluted twofold) by the NML assay. Digoxin concentrations measured by DPC were 0-3.9 p.g/ L in adult patients (NML = LOG x DPC 0.10 zgfL, r2 = 1.00). No “digoxin” was detected by DPC (
