Interference by goat-derived anti-lymphocyte globulin in a double-antibody radioimmunoassay of digoxin

Therapy with anti-lymphocyte and anti-thymocyte globulins, two animal-derived preparations used as immunosuppressive agents, results in high concentrations of foreign immunoglobulin circulating in plasma. We describe a case that illustrates how the presence of these immunoglobulins can interfere with double-antibody radioimmunoassay procedures.