ALB and COVID-19: PCA analysis demonstrated that the main spectral differences between the positive IgM and IgG versus the control were as follows: (1) the features assigned to proteins including albumin were lower in the COVID-19 group as well as in the IgM/IgG and IgG positive group; (2) the features assigned to lipids, phospholipids, and carotenoids were higher in the COVID-19 group and in the IgM/IgG positive group; and (3) the features related to nucleic acids, tryptophan, and immunoglobulins were higher in the COVID-19 group.