Clearance of 25-hydroxyvitamin D in Cystic Fibrosis

Clearance of 25-hydroxyvitamin D in Cystic Fibrosis

The goal of this study is to define 25(OH)D3 catabolism in CF patients using gold standard pharmacokinetics studies. Specifically, the investigators will evaluate the metabolic clearance of 25(OH)D3 among participants with CF and matched control subjects. The goal of this work is to provide the first comprehensive characterization of vitamin D metabolism in CF patients and promote novel hypotheses for subsequent studies.

Inclusion Criteria:

• Age ≥ 18 years
• Serum total 25(OH)D 10-50 ng/mL
• Diagnosis of cystic fibrosis in accordance with CF Foundation Guidelines; OR, normal CONTROL

Exclusion Criteria:

• Primary hyperparathyroidism
• Gastric bypass
• Tuberculosis or sarcoidosis
• Current pregnancy
• Child-Pugh Class B or C cirrhosis (i.e. cirrhosis with ascites, hepatic encephalopathy, bilirubin >=2 mg/dL, serum albumin <=3.5 g/dL, or PT >= 4 seconds)
• History of kidney transplantation or end stage renal disease treated with dialysis
• Use of vitamin D3 or vitamin D2 supplements exceeding a mean daily dose of 400 IU, within 3 months (wash-out allowed)
• Use of 1,25(OH)2D3 or an analogue, calcimimetics, or medications known to induce CYP24A1 within 4 weeks (wash-out allowed)
• Serum calcium > 10.1 mg/dL
• Hemoglobin < 9 g/dL