Correlation of mononuclear phagocyte assay results and in vivo haemolytic rate in subjects with a positive direct antiglobulin test.

A mononuclear phagocyte assay has been used to measure the in vitro interaction of normal donor monocytes with the red cells from subjects with a positive direct antiglobulin test (DAT). The relationship between the in vivo haemolytic rate in these subjects and the results obtained in the assay, expressed as the number of red cells associated with 100 monocytes (ARC value), has been examined. From the results of assays in which normal donor monocytes were incubated with normal (DAT negative) donor red cells it was calculated that ARC values of greater than 2 could be considered significantly elevated. Assays performed on 24 patients with a positive DAT and warm autoimmune haemolytic anaemia resulted in a mean ARC value of 42 (range 1-212). Assay results for two of the patients in this group, however, were not significantly elevated from normal. The red cells from three patients with a negative DAT who were suspected of having autoimmune haemolytic anaemia showed no association with normal donor monocytes in the assay. The mean ARC value obtained for 14 non-haemolysing subjects with a positive DAT was 7 (range 1-47). Assay results for only 10 of the 14 subjects in this non-haemolysing group fell within the normal range. The correlation of assay results and in vivo haemolysis was strengthened when the assays were performed with autologous monocytes. A possible explanation for the unexpectedly low ARC values obtained in some cases of autoimmune haemolytic anaemia is discussed.