Spuriously positive direct antiglobulin tests caused by use of silicone gel.

The direct antiglobulin test using broad-spectrum antihuman globulin was spuriously positive for eight subjects (13%) when red blood cells from silicone gel separation tubes were used. These observations demonstrate that serum separator tubes containing silicone gel have limited use in the blood bank and transfusion service, especially when direct antiglobulin tests must be performed. The tests were positive with anti-C3 reagent, but were negative with anti-IgG when monospecific antihuman globulin was used.