The goal of this observational study is to learn about the effects of cholecalciferol administration, according to guidelines for the general population, on laboratory parameters of Chronic Kidney Disease-Mineral and Bone Disorder in dialysis patients, depending of the attained levels of vitamin D (25OH)D).

The main question it aims to answer is:

How does cholecalciferol affect calcium and phosphate metabolism parameters depending on the achieved levels of 25(OH)D?

Participants taking cholecalciferol as part of their regular medical care for CKD-MBD will have the laboratory result parameters observed for up to 4 years.

The analysis will involve data obtained from medical records of dialysis patients who receive standard procedures consistent with national and international guidelines for specialized care.

Specifically, we will analyze the levels of:

• 25(OH)D,
• 1,25(OH)2D
• Calcium
• Phosphates
• PTH
• FGF23
• GDF15 to assess the efficacy and safety of cholecalciferol in dialysis patients.

Inclusion Criteria:

• CKD stage 5,dialysed patients with vitamin D deficiency or insufficiency (level of 25(OH)D < 30 ng/mL)

Exclusion Criteria:

• dialysis time of less than 3 months
• inadequately controled secondary hyperparathyroidism (iPTH>800pg/mL)
• treatment with calcimimetics
• treatment with active forms of vitamin D3,
• parathyroidectomy
• bilateral nephrectomy
• treatment with corticosteroids
• lack of consent to take part in the study.

Patients will be recruited in Department of Nephrology Transplantology and Internal Medicine, Medical University of Gdansk