The results of the multivariable analysis using logistic regression in combination with the forward selection algorithm and the AIC criterion showed that the risk for the development of a severe disease course for COVID-19 in young patients was higher for combinations of elevated levels of complement C3, increased SAA and SII, and reduced levels of LYM, platelet-lymphocyte ratio (PLR) and uric acid (UA) (Table 3). Here, C3 is linked to COVID-19.