Thimerosal-dependent agglutination complicating the serologic evaluation for unexpected antibodies.

Thimerosal (merthiolate) is a preservative present in several low-ionic-strength blood bank reagents. Thimerosal-dependent panagglutinins were found in the serum of a hospitalized patient during serologic testing for unexpected red cell antibodies. The agglutinins behaved like a mixture of IgG and IgM and reacted with all red cells tested. Once the true nature of the serum panagglutinins was determined, blood bank reagents free of thimerosol were used, and no further serologic problems were encountered. Agglutination of this type should be considered whenever sera appear to contain panagglutinins and thimerosal is present in the test system.