The Correlation between IgM Anti-D and 'Saline Agglutination' of D-positive Cells by Anti-D Sera

S ummary . Sixty-five sera which showed anti-D activity were examined. A saline agglutinating anti-D titre of 1, possibly of 2, does not necessarily imply that the serum contains IgM anti-D, for this agglutination is sometimes due to IgG anti-D in the presence of a sufficient concentration of other protein in the serum. A saline anti-D titre of 4 or higher denotes IgM anti-D.