DIGOXIN-LIKE IMMUNOREACTIVE SUBSTANCE IN THE ELDERLY PATIENT AND ITS IMPACT ON THE TDX DIGOXIN ASSAY

This study was undertaken to examine the impact of endogenous digoxin- like immunoreactive substance (DLIS) on the therapeutic drug monitorin g of digoxin in elderly patients. Serum digoxin concentrations were de tected by TDx digoxin assay in 220 patients 65 years of age and older who were not administered cardiac glycosides, spironolactone, or canre none. The influence of clinical factors and laboratory parameters on t he presence of DLIS was also evaluated. The concentration of DLLS aver aged 0.07 ng/ml (range, 0-0.74 ng/ml), and in 25 subjects DLIS was obs erved over the detection limit of the assay. None of the parameters de monstrated a significant contribution to the presence of DLIS except o ne: continuous intravenous drip infusion therapy with a sodium-contain ing solution (DIV). The frequency of DLIS was significantly higher in the elderly subjects than in 121 control subjects younger than 35 year s of age (p = 0.01). However, the difference became insignificant when subjects administered DIV were excluded from the analysis (p = 0.15). It was suggested that DIV may be clinically important in indicating t he presence of DLIS.