Vitamin D Binding Protein Is Not Involved in Vitamin D Deficiency in Patients with Chronic Kidney Disease

Area of Science:

• Nephrology
• Endocrinology
• Nutritional Science

Background:

• Vitamin D deficiency is common in patients with chronic kidney disease (CKD).
• The role of vitamin D binding protein (VDBP) in vitamin D status in CKD and hemodialysis (HD) patients requires further elucidation.
• Separate determination of 25-hydroxyvitamin D2 (25-OH D2) and 25-hydroxyvitamin D3 (25-OH D3) is crucial for accurate assessment.

Purpose of the Study:

• To evaluate vitamin D status, specifically 25-OH D2 and 25-OH D3 levels, in CKD and HD patients.
• To investigate the relationship between vitamin D levels and VDBP in serum and urine of these patient groups.
• To compare vitamin D and VDBP levels in CKD and HD patients with healthy controls.

Main Methods:

• Cross-sectional study including 45 CKD patients, 103 HD patients, and 25 controls.
• Plasma vitamin D concentrations (25-OH D2 and 25-OH D3) were measured using chromatography.
• Serum and urinary VDBP levels in CKD patients were determined by enzyme immunoassay.

Main Results:

• Plasma vitamin D levels were significantly lower in CKD (30.16 ± 16.74 ng/mL) and HD (18.85 ± 15.85 ng/mL) patients compared to controls (48.72 ± 18.35 ng/mL).
• 25-OH D3 was identified as the predominant form of vitamin D.
• Serum VDBP was elevated in CKD patients (273.2 ± 93.8 ug/mL) compared to controls (222 ± 87.6 ug/mL) and HD patients (213.8 ± 70.9 ug/mL).
• A significant correlation was observed between urinary VDBP and proteinuria in CKD patients (r = 0.43, P = 0.003).

Conclusions:

• Vitamin D deficiency is pronounced in CKD and particularly in HD patients.
• Elevated serum VDBP in CKD patients, despite urinary losses, suggests a compensatory increase in VDBP production.
• Vitamin D binding protein levels do not appear to be directly involved in the pathogenesis of vitamin D deficiency in these patient populations.