Association between glomerular filtration rate and 1,25-dihydroxyvitamin D in cardiac surgery

Renal impairment is a risk factor for poor clinical outcome in cardiac surgical patients and low circulating levels of the vitamin D hormone 1,25-dihydroxyvitamin D (1,25[OH](2)D) may contribute to this risk.

We investigated the association between glomerular filtration rate (GFR) and 1,25(OH)(2)D in 151 heart transplant recipients and 59 other cardiac surgical patients in postoperative week 1 and at postoperative month 1. GFR estimates (eGFR) were calculated from cystatin C (CysC) and serum creatinine (SCr)-based formulas.

With both formulas, linear models provided a better fit between eGFR and circulating 1,25(OH)(2)D than nonlinear models. Nonetheless, the association between 1,25(OH)(2)D and eGFR in the early postoperative period was stronger with the CysC-based formula (r = 0.560; P <0.001) than with the SCr-based equation (r = 0.386; P <0.001). CysC-eGFR and SCr-eGFR displayed considerably lack of agreement in the early postoperative period, especially in heart transplant recipients.

There is a relatively close association between CysC-eGFR and circulating 1,25(OH)(2)D in cardiac surgical patients. Data underline the importance of preserved kidney function in cardiac surgery for adequate circulating 1,25(OH)(2)D levels. The SCr-based formula is probably too imprecise for estimating GFR in the early postoperative period correctly.