Serum Beta(2)-Microglobulin Levels In Coronavirus Disease 2019 (Covid-19): Another Prognosticator Of Disease Severity?

beta(2)-microglobulin (beta(2)-m), a 11.8 kDa protein, pairs non-covalently with the alpha 3 domain of the major histocompatibility class (MHC) I alpha-chain and is essential for the conformation of the MHC class I protein complex. Shed beta(2)-m is measurable in circulation, and various disorders are accompanied by increases in beta(2)-m levels, including several viral infections. Therefore, we explored whether beta(2)-m levels could also be elevated in Coronavirus disease 2019 (Covid-19) and whether they predict disease severity. Serum beta(2)-m levels were measured in a cohort of 34 patients infected with SARS-CoV-2 on admission to a tertiary care hospital in Riyadh, Saudi Arabia, as well as in an approximately age-sex matched group of 34 uninfected controls. Mean beta(2)-m level was 3.25 +/- 1.68 mg/l (reference range 0.8-2.2 mg/l) in patients (mean age 48.2 +/- 21.6) and 1.98 +/- 0.61 mg/l in controls (mean age 48.2 +/- 21.6). 17 patients (mean age 36.9 +/- 18.0) with mean beta(2)-m levels of 2.27 +/- 0.64 mg/l had mild disease by WHO severity categorization, 12 patients (mean age 53.3 +/- 18.1) with mean beta(2)-m levels of 3.57 +/- 1.39 mg/l had moderate disease, and five patients (of whom 2 died; mean age 74.4 +/- 13.8) with mean beta(2)-m levels of 5.85 +/- 1.85 mg/l had severe disease (P < = 0.001, by ANOVA test for linear trend). In multivariate ordinal regression beta(2)-m levels were the only significant predictor of disease severity. Our findings suggest that higher beta(2)-m levels could be an early indicator of severity of disease and predict outcome of Covid-19. As the main limitations of the study are a single-center study, sample size and ethnicity, these results need confirmation in larger cohorts outside the Arabian Peninsula in order to delineate the value of beta(2)-m measurements. The role of beta(2)-m in the etiology and pathogenesis of severe Covid-19 remains to be elucidated.