EVALUATION AND COMPARISON OF THE TDXII, STRATUS, AND OPUS DIGOXIN ASSAYS

Three automated immunoassays for digoxin in serum were evaluated-Abbot t TDxII, Baxter Stratus, and Behring OPUS. The accuracy and precision of the assays were assessed by weighed-in controls and an external qua lity control program. Coefficients of variation of all methods in seru m were less than or equal to 10% at weighed-in concentrations of digox in of 1 and 2.5 mu g/L. Accuracy relative to weighed-in concentrations of 1 and 2.5 mu g/L ranged from 98 to 126% for all methods. Comparati ve results from patient samples showed little difference between the T DxII and Stratus and a greater difference observed between the TDxII a nd OPUS assays. The detection of digoxin-free samples containing digox in-like immunoreactive substances (DLIS) in neonatal cord blood, pregn ant patients, and liver and renal recipients by each assay was then as sessed. The TDxII exhibited the highest incidence of DLIS. This is evi dent in neonatal cord blood in which 40.4% of samples tested positive. In comparison, the extent of DLIS detected by Stratus was less and OP US exhibited no DLIS in any of the groups studied. A case study of a p atient treated with anti-digoxin Fab fragments (Digibind) also was inc luded for analysis by each method. Fourteen hours after Digibind admin istration, the TDxII registered a digoxin concentration of 49.5 mu g/L compared with 3.73, 1.80, and 2.49 mu g/L for Stratus, OPUS, and ultr afiltered TDxII methods, respectively. The results indicate that to de termine the concentration of digoxin after the administration of Digib ind, the OPUS or fluorescence polarization immunoassay (FPIA)-ultrafil tered samples by TDxII are the assays of choice.