COMPARISON OF 4 DIGOXIN IMMUNOASSAYS WITH RESPECT TO INTERFERENCE FROM DIGOXIN-LIKE IMMUNOREACTIVE FACTORS

Objectives: Comparison of a new monoclonal digoxin assay with three po lyclonal digoxin assays for their cross-reactivity to digoxin-like imm unoreactive factors (DLIF) and digoxin metabolites. Design and Methods : Sixty-six nondigitalized patient samples from 5 different groups: ne onates, women in 3rd trimester pregnancy, and patients with liver or r enal diseases, or undergoing organ transplants, and 139 samples from d igoxin-treated patients of 4 categories (hospital sick, liver, renal, and outpatients) were compared in 4 different digoxin assays: (a) ACS( TM) Digoxin (ACS) developed for the automated chemiluminescent Giba Co ming ACS 180(R) system, (b) Baxter Stratus(TM) (Stratus, a fluoroimmun oassay), (c) Ciba-Corning Magic(TM) (Magic, a radioimmunoassay), and ( d) an in-house radioimmunoassay (RIA). The ACS(TM) and RIA were also c ompared for their cross-reactivity to four principal digoxin metabolit es. Results and Conclusion: Among the nondigitalized specimens, no sig nificant DLIF interference was found for all 4 assays among the pregna nt women or liver and transplant patients. However, the neonates regis tered high DLIF interference with Magic(TM) and RIA, but none for ACS( TM) or Stratus(TM). DLIF interference in renal samples was highest in the Magic assay and lowest in RIA. Among the specimens with digoxin, a higher number of discrepant samples were found from the sick patients than from outpatients. In 75% of such discrepant samples, the ACS(TM) result was less than other assay results, suggesting DLIF as the prob able cause. The two assays differed most in their cross-reactivity to the deglycated metabolites, digoxigenin and its mono-digitoxoside.