Positive antiglobulin test in association with sulindac: involvement of the Rh factor.

We investigated the development of a positive direct antiglobulin test associated with the use of the nonsteroid anti-inflammatory drug sulindac. The drug was shown to be the cause of the positive direct antiglobulin test using red cells treated in vitro with solutions of native sulindac and its two major metabolites. Serum from the patient contained sulindac-dependent red cell antibodies which could not be demonstrated when red cells having the Rh phenotype D-- were employed in the test procedure. An eluate prepared from the patients' red cells reacted against untreated red cells having common Rh phenotypes, but not against target red cells with the Rh phenotypes D-- or Rh null. The eluate showed stronger reactivity against the cells having common Rh phenotypes when they were treated with solutions of a metabolite of sulindac, but failed to react against treated red cells having the Rh phenotype D-- or Rh null. The results of our investigations point to an interaction between sulindac and/or its metabolites and Rh structures on the red cell membrane as the initial step in the production of drug dependent and autoantibodies leading to the positive direct antiglobulin test.