A cryoglobulin with cold agglutinin and erythroid stem cell suppressant properties.

A 93-year-old woman presented with profound anemia (hematocrit 23% [0.23]); there was clumping of her red cells in test tubes and on peripheral blood smears. There was also a marked decrease in erythroid precursors in the bone marrow and reticulocytopenia in the peripheral blood. An IgM kappa monoclonal gammopathy was found in low concentration (approximately 1%) in her serum, and the cold agglutinins had a titer of 2560. However, the cold agglutinin titer of the supernatant after cryoglobulin precipitation was 40. Redissolving the cryoglobulin in the supernatant resulted in a cold agglutinin titer of 1280. Moreover, the addition of the patient's whole serum inhibited erythroid colony formation in culture. The inhibition was removed by cryoprecipitation of the cryoglobulin. The patient was given steroid therapy, to which she responded with reticulocytosis and an elevation of hematocrit. By 3 months, the cold agglutinin titer had fallen to 10. She remained well 4 years later. Whereas reports of cryoprecipitable cold agglutinins are rare, this case is unique because there have been no previous reports that these cold active proteins also have erythroid stem cell-suppressant properties.