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. 2024 Apr;72(2):185-196.
doi: 10.1007/s12026-023-09434-9. Epub 2023 Nov 23.

Insights into the immunological description of cryoglobulins with regard to detection and characterization in Slovenian rheumatological patients

Manca Ogrič  1 , Tinka Švec  1 , Katjuša Mrak Poljšak  1 , Katja Lakota  1   2 , Eva Podovšovnik  3 , Marie Nathalie Kolopp-Sarda  4   5 , Alojzija Hočevar  1   6 , Saša Čučnik  7   8
Affiliations

Insights into the immunological description of cryoglobulins with regard to detection and characterization in Slovenian rheumatological patients

Manca Ogrič et al. Immunol Res. 2024 Apr.

Abstract

The detection of cryoglobulins (CG) used to diagnose cryoglobulinemic vasculitis requires strict adherence to protocol, with emphasis on the preanalytical part. Our main objectives were to introduce a more sensitive and specific protocol for the detection of CG and to characterize CG in Slovenian patients diagnosed with cryoglobulinemic vasculitis, other vasculitides, connective tissue diseases or non-rheumatic diseases examined at the Department of Rheumatology (University Medical Centre Ljubljana). Samples were routinely analyzed for the presence of CG with the protocol using the Folin-Ciocalteu reagent. In the newly introduced protocol, the type of CG was determined by immunofixation on visually observed positive samples and the concentration of CG in the cryoprecipitate and rheumatoid factor (RF) activity were measured by nephelometry. RF, C3c and C4 were measured in patients` serum and a decision tree analysis was performed using all results. The agreement between negative and positive results between the two protocols was 86%. Of the 258 patient samples tested, we found 56 patients (21.7%) with positive CG (37.5% - type II, 62.5% - type III). The RF activity was observed in 21.4% of CG positive subjects. The median concentration of type II CG was significantly higher than that of type III CG (67.4 mg/L vs. 45.0 mg/L, p = 0.037). Patients with type II had lower C4 concentrations and higher RF compared to patients with type III CG. In the decision tree, C4 was the strongest predictor of cryoglobulinemia in patients. With the newly implemented protocol, we were able to improve the detection and quantification of CG in the samples of our rheumatology patients and report the results to adequately support clinicians.

Keywords: Complement components; Cryoglobulin detection; Cryoglobulinemic vasculitis; Cryoglobulins; Pre-analytical phase; Rheumatoid factor activity.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Graphical representation of sampling, visual observation and isolation of CG. Legend: CG – cryoglobulins, PBS – phosphate buffered saline. The figure was created with BioRender
Fig. 2
Fig. 2
Examples of immunofixation gels used to determine cryoglobulin type (A-C: Type II CG, polyclonal IgG and monoclonal IgM kappa, D-F: Type III CG, polyclonal IgG and IgM (D) and polyclonal IgG and IgA (E-F))
Fig. 3
Fig. 3
Comparison between CG concentrations (A), RF (B), C4 (C) and C3c (D) in serum between the patients with type II or type III CG. Legend: CG – cryoglobulins, RF – rheumatoid factor. Asterisks are used as follows: * for p < 0.05 and ** for p < 0.001
Fig. 4
Fig. 4
Comparison between CG concentrations (A), RF (B), C4 (C) and C3c (D) in serum between the patients with type II CG with or without RF activity in CG precipitate or type III CG with or without RF activity in CG precipitate Legend: CG – cryoglobulins, RF – rheumatoid factor. Asterisks are used as follows: * for p < 0.05 and ** for p < 0.001
Fig. 5
Fig. 5
Decision tree structure (CHAID assay) for cryoglobulinemia, cut-off values of predictive immunological variables: C4 (4 groups with ranges) and RF (negative RF – 0, positive RF – 1). Legend: CG – cryoglobulins, neg – negative CG result, pos – positive CG result, RF – rheumatoid factor
See this image and copyright information in PMC

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