'Hypocryoglobulins'. Enhanced cryoprecipitation from hypotonic serum in patients with vasculitis

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Abstract
Three patients with cutaneous vasculitis and 1 patient with digital gangrene had a negative or equivocal test for cryoglobulins but a positive result in a modified assay for cryoproteins (hypocryoglobulins [HG]) in which serum is rendered hypotonic by dilution with an equal volume of distilled water before incubation in the cold. Each cryoprecipitate contained a mixture of Ig and in 2 instances, a monoclonal component was demonstrated. Rheumatoid factor activity was found in 2 precipitates. All 4 patients improved with plasmapheresis and 2 subsequently responded to alkylating agents. Seven patients with conventional cryoglobulins had precipitation from diluted serum as well, but none had a substantial increase in precipitation in the HG assay. Only 2 of 5 patients with seropositive rheumatoid arthritis had abnormal levels of HG. Hypocryoglobulins are a new category of abnormally insoluble serum proteins, probably closely related to conventional cryoglobulins, which are readily detected in a simple precipitation assay.