Cryoglobulin deposits on a blood smear.

A 61-year-old male presented with 2 months of bone pain. Complete blood count showed Hb 10 g/dL, white blood cell count 4.5 109/L, and platelets 130 109/L. The peripheral smear contained visible agglutinates and a blue background color (panel A). Aggregates of amorphous particles mimicking lysed cells were observed microscopically (panels C-E) with smaller and less stained deposits (panel E arrow), some resembling platelets (panel E stars). These findings suggested cryoglobulins. After warming the blood (37°C 4 hours), the smear regained its usual staining characteristics (panel B) and was free of microscopic deposits. A serum prepared at 37°C demonstrated protein precipitation when cooled to room temperature. This was determined to be an IgG, monoclonal protein (29.3 g/L). Afterward, the patient was noted to have sternal and vertebral lytic lesions. Bone marrow examination revealed 34% plasma cells, and a diagnosis of mutliple myeloma was made.