Significances of red cell bound immunoglobulin G as detected by flow cytometry in patients with Coombs-negative immune hemolysis.

OBJECTIVES: This study was to investigate the use of flow cytometry for detection and quantitation of red blood cells (RBC) bound IgG in immune hemolysis of patients with autoimmune hemolytic anaemia (AIHA) and systematic lupus erythematosus (SLE).

BACKGROUND: Two to ten percent of patients with warm-autoimmune hemolytic anaemia (WAIHA) exhibit a negative direct Coombs test. Flow cytometry has been applied to detect RBC bound IgG with high accuracy, reproducibility and sensitivity.

METHODS: In this study 45 and 75 patients with AIHA and SLE, respectively were evaluated for RBC bound IgG by direct Coombs test and flow cytometry.

RESULTS: Seventy-one percent (32/45) and 31% (23/75) of patients with AIHA and SLE respectively, had laboratory evidence of hemolysis. A positive flow cytometry, as defined by mean fluorescent intensity (MFI) values >0·21 and IgG molecules >28, was found in 4 of 32 (12·5%) and 4 of 23 (17·4%) patients with AIHA and SLE who had hemolysis with a negative direct Coombs test. There were very strong and strong correlations between the strength of direct Coombs test with MFI values and IgG molecules in patients with AIHA and SLE, respectively.

CONCLUSION: Flow cytometry can be applied in the diagnosis of Coombs-negative hemolytic anaemia in patients with AIHA and SLE.