Cytomegalovirus mononucleosis with mixed cryoglobulinemia presenting transient pseudothrombocytopenia

A 61-year-old man was admitted to our hospital because of fever and general malaise. We diagnosed his condition as cytomegalovirus (CMV) mononucleosis by hematological testing. His platelet count was decreased in spite of collection with several anticoagulants at room temperature (20 degrees C); no decrease was observed at 37 degrees C. Mixed cryoglobulinemia, monoclonal IgM and polyclonal IgG, which acted as anti-platelet antibodies in cold condition, were found in the patient's serum. With the resolution of CMV infection, the cryoglobulins disappeared and the platelet count returned to normal without platelet agglutination. This is the first report of transient pseudothrombocytopenia in CMV mononucleosis with mixed cryoglobulinemia.