Abstract
Digoxin-like immunoreactive substances are an endogenous group of compounds that cross-react in conventional immunoassays for digoxin. Plasma digoxin-like immunoreactive substance concentrations were estimated using the Abbott TDxll fluorescence polarisation immunoassay kit for digoxin. Digoxin-like immunoreactive substances were measured in one hundred consecutive Intensive Care Unit (ICU) patients who were not treated with digoxin. One hundred healthy blood donors were used as controls. Thirty of the ICU patients had plasma digoxin-like immunoreactive substance concentrations greater than or equal to the greatest value found in the control group (0.22 nmol/l). In the ICU group the median value was 0.17 nmol/l and the range zero to 1.69 nmol/l. In the control group the median was less than the limit of detection of the assay, and the range zero to 0.22 nmol/l. Sixteen ICU patients had coexisting renal and hepatic dysfunction and this group had a median digoxin-like immunoreactive substance concentration of 0.21 nmol/l (range zero to 1.69 nmol/l), while 38 patients with hepatic dysfunction and normal renal function had a median concentration of 0.17 nmol/l (range zero to 0.77 nmol/l). In contrast four patients with renal dysfunction only had a median concentration of 0.05 nmol/l (range zero to 0.34 nmol/l). The remaining forty-two patients had neither hepatic nor renal dysfunction and this group had a median concentration of 0.15 nmol/l (range zero to 0.36 nmol/l). This study has identified the critically ill as a group of patients who exhibit measurable plasma digoxin-like immunoreactive substances using the most commonly used kit for analysis of digoxin.