Cryofibrinogen—Characteristics and Association with Cryoglobulin: A Retrospective Study Out of a Series of 1,712 Samples over 7 Years

Objective Cryofibrinogens (CFs) and cryoglobulins (CGs) are cryoproteins responsible for obstructive vasculopathy and vasculitis. The aim of this study was to compare the characteristics of CF and CG, and to define the conditions of their association. Methods and Results This retrospective study was conducted at the Lyon University Hospitals, and included patients with at least one sample tested for CF and/or CG between September 2013 and April 2021. Serum and plasma samples were analyzed in very strict conditions of temperature. After cold precipitation, CF and CG were characterized and quantified in the cryoprecipitates. CRP and plasma fibrinogen levels were also investigated. Over this 7-year period, 1,712 samples for CF detection and 25,650 samples for CG detection were sent to the laboratory. Simultaneous testing of CF and CG was performed in 1,453/1,712 samples (85%). CF was less often positive than CG (8.3 vs. 13.5%, p < 0.0001). In positive CF samples, CG was associated in 28.9% of cases. In CF, fibrinogen was associated with fibronectin in 98/142 (69%) samples, especially in highly concentrated CF. CF concentration was independent of C-reactive protein and plasma fibrinogen concentrations. Conclusion The simultaneous detection of CF and CG is essential for the diagnosis of vasculitis or thromboembolic events and their treatment.