Abnormal vitamin D metabolism and loss of bone mass after renal transplantation

Osteoporosis is a major complication after renal transplantation. The most important causative factor is the use of corticosteroids, but abnormalities in vitamin D metabolism and persisting hyperparathyroidism could also be involved. The present study examines changes in vitamin D metabolites, intact parathyroid hormone, and bone mineral density (BMD) during the first 2 years after renal transplantation.

Sixty-one patients (38 male, 23 female; age 42 +/- 13 years) who received a renal transplant participated in the study. Immunosuppressive treatment consisted of ciclosporin and prednisone. Laboratory parameters and BMD (lumbar spine and hip) were measured at baseline and 1 (laboratory only), 3, 6, 12, and 24 months after transplantation.

At the time of transplantation, the 1,25-dihydroxyvitamin D levels were low in all patients. Although we observed a gradual increase, subnormal values were still present in 39 (64%) and 29 (47%) patients 3 and 6 months after transplantation, respectively. From 3 months after transplantation the 1,25-dihydroxyvitamin D level correlated with the creatinine clearance. After transplantation, the intact parathyroid hormone levels declined rapidly to values slightly above normal. The lumbar BMD was nearly normal at the time of transplantation, but decreased rapidly within 6 months (-6.5 +/- 4.5%; p < 0.001). A smaller decrease occurred in the femoral neck (-4.1 +/- 6.5%; p < 0.001), in Ward's triangle (-2.4 +/- 13.0%; p < 0.01), and in the trochanter (-5.1 +/- 6.3%; p < 0.001). After 6 months, the bone mass stabilized.

The vitamin D metabolism remains disturbed for a considerable time after renal transplantation. In nearly half of the patients, the levels of active vitamin D remain abnormal for at least 6 months. The BMD decreased during the first 6 months after transplantation and remained stable thereafter. We speculate that the observed abnormalities in vitamin D metabolism may contribute to the early bone loss after renal transplantation.