To the Editor.
—A recent report in the Archives1 concerning the possible role of sulindac in immune hemolytic anemia raises questions about the mechanism of the action of this drug in this process, and the means by which this was demonstrated.If the authors postulate a haptenic mechanism (eg, as with penicillin), then the most suitable means of demonstrating this is to test an eluate from the patient's red blood cells with sulindac-coated reagent red blood cells, and with uncoated reagent red blood cells. This can demonstrate that the drugrelated antibody is responsible for the positive direct antiglobulin test.As the authors used patient serum as the source of the antibody, its reactivity should have been tested against uncoated reagent red blood cells. The presence of a warm autoantibody would preclude this testing; however, this would then make definitive conclusions impossible. Also, normal serum should have been tested against