Patterns of renal osteodystrophy 1 year after kidney transplantation

Renal osteodystrophy is considered common, but is not well characterized in contemporary kidney transplant recipients. This study reports extensively on bone phenotype by bone histomorphometry, bone densitometry and novel bone biomarkers 1 year after kidney transplantation.

A transiliac bone biopsy and dual-energy X-ray absorptiometry scans were performed in 141 unselected kidney transplant recipients in this observational cohort study. Blood and 24-h urine samples were collected simultaneously.

The median age was 57 ± 11 years, 71% were men and all were of Caucasian ethnicity. Bone turnover was normal in 71% of patients, low in 26% and high in just four cases (3%). Hyperparathyroidism with hypercalcaemia was present in 13% of patients, of which only one had high bone turnover. Delayed bone mineralization was detected in 16% of patients, who were characterized by hyperparathyroidism (137 versus 53 ρg/mL), a higher fractional excretion of phosphate (40 versus 32%) and lower levels of phosphate (2.68 versus 3.18 mg/dL) and calcidiol (29 versus 37 ng/mL) compared with patients with normal bone mineralization. Osteoporosis was present in 15-46% of patients, with the highest prevalence at the distal skeleton. The proportion of osteoporotic patients was comparable across categories of bone turnover and mineralization.

The majority of kidney transplant recipients, including patients with osteoporosis, have normal bone turnover at 1-year post-transplant. Low bone turnover is seen in a substantial subset, while high bone turnover is rare. Vitamin D deficiency and hypophosphataemia represent potential interventional targets to improve bone health post-transplant.