Correlation matrix between serum 25(OH)D and other biomarkers. 25(OH)D – 25-hydroxy vitamin D; IL-6 – Interleukin-6; LDH – Lactate dehydrogenase; CK – Creatine kinase; DD – D-dimer; CRP – C-reactive protein; PCT – Procalcitonin; ESR – Erythrocyte sedimentation rate.