The investigators will be measuring vitamin D metabolites in blood samples drawn from patients undergoing cardiac surgery to determine the correlation with renal function as assessed by serum creatinine. The investigators will include 20 patients in each of the following 3 groups based on serum creatinine measured within 28-days of surgery: 1) normal kidney function (eGFR > 60 mL/min, n=20), 2) moderate impaired kidney function, eGFR between 30 and 60 mL/min (n=20) and 3) severe kidney dysfunction eGFR < 30 mL/min (n=20).

Inclusion Criteria

• ≥ 18 years
• Patients undergoing cardiac surgery
• Serum Creatinine measured with 28 days of surgery

Exclusion Criteria

• Exogeneous calcitriol (1,25(OH)2D3) intake
• History of parathyroidectomy
• Patients with liver or kidney cancer
• Patients with liver disease (e.g. liver failure, cirrhosis)

Patients undergoing cardiac surgery .

Data from this study is unique to the study and analytical techniques used