Positive Direct Coombs' Test Induced by Various Azo Dyes.

Summary In an earlier investigation the activity of the diazo dye trypan blue in producing an anemia with positive Coombs' test was attributed primarily to its capacity for binding with protein and thus either altering the surface of erythrocytes or serving as a prosthetic group for the attachment of serum proteins. The present study of the activity of a number of structurally related compounds supports this hypothesis, for only those dyes which appeared in the serum in high concentration, with a large proportion of non-protein bound (free) dye, induced protein coating of the erythrocytes. In general, the active dyes had structural formulae similar to trypan blue and the diazo linkage, as well as the presence of the amino group, appeared to be essential.