Hyperviscosity syndrome caused by cryoglobulinemia diagnosed by observing the reversible formation of gel upon cooling and warming the patient's serum

A 74-year-old woman with a 3-month history of general malaise and loss of appetite was referred to our unit for investigation of hyperviscosity syndrome. The patient had initially attended her local hospital reporting cyanosis and mild oedema of the toes on both her feet. She also had splenomegaly and polyclonal gammopathy: IgG concentration was 3320 mg/dL (typical range 861–1747), IgA was 508 mg/dL (typical range 93–393), and IgM 1648 mg/dL (typical range 50–269). The progressive hyperviscosity of the patient's blood specimens made further testing difficult, hence the referral to our hospital.