P041 Immunological characteristics and distribution of cryoglobulins in a cohort of 13000 patients over 6 years

Career situation of first and presenting author Assistant. Introduction Cryoglobulins (CG) are immunoglobulins (Ig) that precipitate in vitro at cold temperature and dissolve at 37°C, they are classified in 3 types. Type I CG are monoclonal Ig of IgM or IgG isotype. Type II and III are mixed CG: type II CG associate a monoclonal with polyclonal Ig, type III CG associate polyclonal Ig. Rheumatoid factor activity (RF) of mixed CG leads to the formation of immune complexes that can precipitate and result in vasculitis. Objectives The purpose of this study was to update information on CG biological characteristics in a large population recruited from all clinical departments of a French University Hospital. Methods This retrospective study was conducted from January 2010 to December 2016. Patients included had at least one serum sample for CG detection and characterization: CG isotype and clonality, concentration and RF (IgM anti-IgG) in the cryoprecipitate; and serum complement exploration. Associated pathologies were determined by biological markers of gammopathy, viral infection and autoimmunity. Results A total of 13439 patients were included, 1675 (12,5%) of whom had positive CG. In case of negative CG detection, 2213 patients were retested and CG was detected on the new sample for 196/2213 patients (8.9%). Type I CG was found in 9.3% (155/1675), type II CG in 47% (788/1675), and type III CG in 43.7% (732/1675) of patients. In type I CG, IgM CG was more frequent than IgG CG, but in lower concentration (p=0.02). For mixed CG, 34.8% of HCV+ tested patients had CG, less than 5% of CG was associated with HBV+ or HIV+ serology. Mixed CG were found in 25.4% of patients with anti dsDNA, anti-SSA60 or anti-CCP autoantibodies (Ab). Mixed CG were positive for 87/333 (26.1%) patients with anti-dsDNA Ab, 74/447 (16.6%) patients with anti-SSA60 Ab, and for 19/155 (12.3%) patients with anti-CCP Ab. Both the cryoprecipitate and the serum were positive for RF in 21.6% of type II CG and 10.1% of type III CG. C3, C4 and/or CH50 decrease was found in 23.6% of serum with CG vs 3.2% of CG-negative serum (p Conclusions In this largest cohort even studied, with patients from all clinical specialties, CG distribution and characteristics were described with minimal selection bias. Despite strict pre-analytical conditions, negative CG detection must be repeated according to clinical context. Mixed CG are more frequently detected in patients positive for HCV or anti-dsDNA Ab. CG with RF activity form immune complexes that precipitate in vessels and activate complement system, responsible for cryoglobulinemic vasculitis. Disclosure of Interest None declared.