Vitamin D deficiency may predispose patients to increased risk of kidney transplant rejection.

Background: Vitamin D deficiency occurs in more than 80% of kidney transplant recipients. Its immunomodulatory effects can predispose transplant recipients to rejection and chronic allograft nephropathy (CAN). This study determined the association between serum 25 (OH) vitamin D, biopsy-proven allograft rejection, and CAN rates.

Aim: To determine the relationship between serum 25 (OH) vitamin D level and biopsy-proven allograft rejection and CAN rate in renal transplant recipients.

Methods: Adult renal transplant recipients followed at the clinic between January 2013 and 2018 were included. Recipients requiring graft biopsy due to declined function, hematuria, and proteinuria were reviewed. The two groups were compared regarding collected data, including the biopsy results, immunologic parameters, vitamin D, parathyroid hormone (PTH), phosphorus, albumin levels, and graft function tests.

Results: Fifty-two recipients who underwent graft biopsy met the inclusion criteria. In all, 14 recipients had a vitamin D level > 15 ng/mL (group 1) vs ≤ 15 ng/mL (group 2) in 38. In total, 27 patients had biopsy-proven rejection, and 19 had CAN. There was only 1 recipient with biopsy-proven rejection in group 1, whereas there were 24 patients with rejection in group 2. The rejection rate was significantly higher in group 2 than in group 1 (P < 0.001). Four patients were diagnosed with CAN in group 1 vs fifteen in group 2. There was no significant difference in the CAN rate between the two groups. PTH was higher at the time of graft biopsy (P = 0.009, P = 0.022) in group 1 with a mean of 268 pg/mL. Donor-specific antibodies were detected in 14 (56.0%) of the recipients with rejection. Vitamin D level was 9.7 ± 3.4 ng/mL in the rejection group vs 14.7 ± 7.2 in the non-rejection group; this difference was statistically significant (P = 0.003). The albumin levels were significantly lower in patients with rejection than in those without rejection (P = 0.001). In univariate regression analysis of risk factors affecting rejection, sex, serum vitamin D, phosphorus and albumin were found to have an impact (P = 0.027, P = 0.007, P = 0.023, P = 0.008). In multivariate regression analysis, the same factors did not affect rejection.

Conclusion: The serum 25 (OH) vitamin D level in kidney transplant recipients remained low. Although low serum vitamin D level emerged as a risk factor for rejection in univariate analysis, this finding was not confirmed by multivariate analysis. Prospective studies are required to determine the effect of serum vitamin D levels on allograft rejection.