Positive Direct Coombs Test Induced by Phenylhydrazine1

The Coombs or antiglobulin test was introduced for the detection of antibodies to erythrocytes of a type termed "incomplete antibodies " (1). The indirect Coombs test has gained wide application in the detection of the antibodies to various eryth-rocytic antigens (2) and in the cross-matching of blood for transfusions (3). The direct Coombs test has become a diagnostic and investigative tool in hemolytic disease of the newborn (4-6), fol-lowing incompatible blood transfusions (7) and in the acquired hemolytic anemias, idiopathic or secondary types (8-22). All of these conditions in man when associated with positive direct and indirect Coombs tests, have been interpreted to be the result of immune mechanisms, either of the isoimmune or autoim-mune type. In the present communication the pro-duction of a positive direct Coombs test in the dog by means of the drug phenylhydrazine is de-scribed. The phenomenon is unattended by the immunologic implications of blood incompatibility and is not associated with the usual conditions causing a secondary or symptomatic acquired he-molytic anemia. MATERIAL AND METHODS Adult normal mongrel dogs of either sex weighing 5.5 to 11 kg. were used. After the control observations had been completed, a 1 to 2 per cent solution of phenyl-hydrazine hydrochloride (Merck) in saline was injected intravenously in a single dose of 40 mg. per kg. body weight. The studies were conducted periodically there-after up to 41 days. The hemoglobin concentration of the peripheral blood was determined by the alkaline hematin method (23). The hematocrit was determined according to Wintrobe (24) and the reading was corrected for trapped plasma according to the method of Chaplin and Mollison (25). Reticulocytes were estimated routinely by counting 1000 erythrocytes stained with brilliant cresyl blue (26). Heinz bodies were stained with 0.2 per cent methyl violet