A 73-year-old lady who has a history of diabetes mellitus and otherwise healthy presented with acute abdominal pain and a history of recent onset fatigue. Laboratory evaluation showed WBC 10.9K/mL, RBC 2.29K/mL, Hb 7.3g/dL, HCT 23.6%, MCV 103.1, RDW 18.6% and platelet count 344K/mL. PT and PTT were within normal limits. A gastrointestinal scopy showed non-bleeding gastric ulcers and no other source of bleeding. The occult blood test was negative. H.pylori IgG was positive. Further evaluation showed haptoglobin of <32mg/dL and positive polyspecific direct Coomb's test. Parvovirus serology was negative and flow cytometric analysis for PNH was negative.

A bone marrow biopsy was performed. The peripheral blood smear showed significant red cell agglutination and rosetting of red cells around the neutrophils. There were polychromasia and a few circulating nucleated red cells. There were no schistocytes. 

Bone marrow was hypercellular (70%) with erythroid hyperplasia (ME ratio 1:3). The aspirate smear showed rare fat granulomas. The biopsy showed rare fat granulomas. Flow cytometry showed an inverted CD4/CD8 ratio and no immunophenotypically abnormal cell populations. The cytogenetic evaluation showed a normal female karyotype. 

A diagnosis of autoimmune hemolytic anemia (AIHA) was made. The patient received multiple blood transfusions and was started on corticosteroids. She responded well and on follow up is asymptomatic with a  hemoglobin level of 10g/dL. 

Leukocyte erythrocyte rosettes are hypothesized to form through an interaction of surface Fc receptors and erythrocytes coated with IgG. These rosettes are thought to precede extravascular red blood cell destruction and are predictors of AIHA. 

Reference:

Zupanska B. Rosetting, phagocytosis and immune red cell damage. Clin Lab
Haematol 1990;12:309–320.