Positive Direct Coombs Test Induced by Phenylhydrazine1

Abstract

Phenylhydrazine has produced a positive direct Coombs test in the dog. The agglutination was stable when the drug was injected intravenously in doses of 40 mg/kg. A transient and unstable agglutination occurred when the drug acted on the red blood cells (RBC) in the test tube. The phenomenon is not considered due to an immunologic mechanism because of its sudden onset, short-lived status and the lack of potentiation by repeated doses. It is considered that the positive direct Coombs test results from an alteration of erythrocytes by phenylhydrazine or some breakdown product of phenylhydrazine. Three possibilities are considered: alteration of the surface of the erythroyctes so as to make it act directly as receptors for antibodies in the Coombs serum; alteration of erythrocytes so as to cause adsorption of non-immune proteins; the possibility that the drug acts as a coupling agent between erythrocytes and non-immune proteins as plasma proteins.