Cryoglobulinemia Is More Frequently Associated with IgM Paraproteins Than Previously Reported, Interfering with Their Quantification, and Resulting in Potential Treatment Delays

Type 1 Cryoglobulins are more commonly found in IgM paraproteins than previously reported (26% v 6%).¹ The presence of cryoglobulins can result in an underestimation of paraprotein quantification (>50%) changing clinical management.

A cryoglobulin screen or paraprotein quantification at 37⁰C may need to be routinely performed in high-risk individuals irrespective of hyperviscosity symptoms to allow safer monitoring of patients.

Method: Business Services Organisation Laboratory Information Management System was used to extract patients with IgM paraproteins from the 1/1/2021 to 1/1/2022. 41 Patients were obtained of which 18 were excluded.

23 patients were recruited with a statistical power of 87%. These 23 patients attended to have temperature-controlled venepuncture allowing assessment of paraprotein and cryoglobulin at body temperature. The samples were retested at room temperature and at 5⁰C to demonstrate possible temperatures paraproteins are routinely checked in the laboratory.

Statistical analysis of results was carried out on MedCalc. Numerical variables were first assessed for normality distribution using Shapiro-Wilk test of normality. Wilcoxon signed-rank test was used as the data did not meet parametric assumptions. Kruskal-Wallis test was used to determine the significance between paraprotein levels and related IgM disease. Analysis of the temperature data was assessed using Prism GraphPad and results analysed using paired t-test.

Results: The 23 patients recruited consisted of 14 male and 9 females with a median age of 74 comparable with the national LPL statistics.²

An underlying LPL disorder was seen in 70% (n=16) of patients within this study, the remainder had IgM MGUS 13% (n=13), 9% (n=2) IgM related disease and 9% with other lymphomas (CLL, MZL) representing the population recruited through the haematology unit rather than general population.

26% of patients tested positive for cryoglobulinemia (n=6), 5 of the 6 of patients with cryoglobulinemia had an underlying LPL diagnosis, while only one patient had MZL. Overall, the study found a higher-than-expected detectable cryoglobulin incidence of 31% amongst the LPL cases. Sub-analysis of the patients with a detectable cryoglobulin worryingly found 5 of 6 had an underestimation of their paraprotein. Table 1 shows the paraprotein quantification at 5⁰C, RT 19⁰C and body temperature 37⁰C across all the recruited patients. Although overall the change was not statistically significant (p=0.71) given sample population size, this did result in a clinical change in management for these patients. As we can see from graph 1 in the patients with cryoglobulins the difference in paraprotein quantification between the extreme of temperatures becomes more evident as the protein size increased.

Clinical Implication: Cryoglobulin is an underutilised test within clinical practice because of its complexity, turn-around times, and the requirement of maintaining adequate temperature control (>370C).³ There is no worldwide standard testing method.^4,5,6 As thermal control equipment has improved, cryoglobulins may previously have been underreported.

Given the study population size, significance is hard to prove but this has raised clinical concern and resulted in a patient receiving treatment due to hyper viscosity risk. In this case the paraprotein at body temperature was 43g/l IgM. However as previous paraproteins were analysed at RT (19g/l) or out of the overnight fridge at 5⁰C (13g/l), These misleading results allowed this patient to be followed up too long. This study has found a cohort of patients with cryoglobulins and discordant paraproteins across the thermal range. The identified patients have been flagged to have paraproteins quantified at 37⁰C.

The high frequently of cryoglobulins is interesting in IgM paraproteins and concerning given their potential to interfere with paraprotein quantification. Accurate paraproteins are crucial in the diagnosis of IgM disorders, monitoring disease progression, relapse, guiding treatment initiation and response.^7,8

A change in clinical practice would be appropriate initially to test all IgM paraproteins at body temperature and allowing to cool and re-quantifying their paraprotein. This would ensure in vivo paraproteins are being accurately assessed and may also act as an indirect test for cryoglobulin if a discrepancy is found.

No relevant conflicts of interest to declare.