Evaluation of Vitamin D binding protein and 25-hydroxy Vitamin D metabolites in COVID-19 patients

INTRODUCTION: The immunomodulatory roles of Vitamin D and Vitamin D binding protein (VDBP) are in interest with incidence or outcome of coronavirus disease-2019 (COVID-19). This study aimed to investigate the association between the severity of COVID-19 with VDBP, total 25-hydroxy Vitamin D (25(OH)D), and its metabolites free Vitamin D (VDfree) and bioavailable Vitamin D (VDbio).
METHODS: Study group consisted of 68 COVID-19 patients and 20 healthy subjects. Patients were subgrouped as asymptotic, mild/moderately pneumonia, or severe pneumonia. Plasma total 25(OH)D was quantitated by liquid chromatography with mass spectrometry and serum VDBP by a polyclonal sandwich enzyme immunoassay. In addition, routinely used laboratory parameters in follow-up were recorded. VDfree and VDbio were calculated using total 25(OH)D, VDBP, and albumin levels.
RESULTS: Plasma total 25(OH)D (13.3±5.7 vs. 30.3±13.3 ng/dL), VDfree (2.18 [1.52–3.44] vs. 4.34 [3.74–6.48] pg/mL), and VDbio (1.86 [1.09–2.81] vs. 4.28 [3.45–6.34] nmol/L) levels were lower in COVID-19 patients (p<0.001). Despite the in-significance of 25(OH)D and metabolites between COVID-19 severity subgroups, serum VDBP was highest in mild/moderately pneumonia (601.8±278.6 ng/mL) and lowest in severe pneumonia (427.9±147.2 ng/mL) (p<0.001). In addition, VDBP was positively correlated with lymphocyte counts (B: 87.9, r2=0.068, p=0.031) and negatively correlated with D-Dimer levels (B: −0.024, r2=0.081, p=0.032).
DISCUSSION AND CONCLUSION: COVID-19 patients have lower plasma 25(OH)D levels and lower 25(OH)D metabolites VDfree, VDbio which are physiologically active. In addition, serum VDBP concentrations significantly decrease in critically ill patients which needs further studies to be associated in the etiopathogenesis of the disease severity.