Applicability of fibroblast growth factor 23 for evaluation of risk of vertebral fracture and chronic kidney disease-mineral bone disease in elderly chronic kidney disease patients

Background: Elderly patients with chronic kidney disease (CKD) are usually at a high risk of fractures due to both osteoporosis and CKD-mineral bone disease (MBD). A new marker is needed to prevent fractures and control CKD-MBD from the early to advanced stages of CKD. In the early stage of CKD, fibroblast growth factor 23 (FGF23) level increases before parathyroid hormone (PTH) and phosphate levels increase, and steadily increases with the progression of kidney disease. It has been reported that FGF23 is related to the overall fracture risk. We investigated the usefulness of FGF23 as a marker for evaluating the risk of vertebral fracture and CKD-MBD in elderly CKD patients. Methods: One hundred and five elderly predialysis CKD patients who had never been treated for osteoporosis and had never used calcium supplements, vitamin D supplements, or phosphate binders were enrolled in this cross-sectional study in Tokyo, Japan. We investigated the prevalence of vertebral fracture and measured serum calcium, phosphate, 1,25(OH)(2) vitamin D [1,25(OH)(2)D], intact PTH, FGF23, alkaline phosphatase, and urinary N-terminal telopeptide levels. Then, we examined the relationship between the level of FGF23 and those of bone-metabolism-related markers and identified markers associated with vertebral fractures in elderly CKD patients. Results: The background features of the patients were as follows: female, 32.4%; diabetes mellitus, 39.0%; average age (standard deviation), 73.2 (7.7) years; and estimated glomerular filtration rate (eGFR), 45.7 (24.1) ml/min/1.73 m(2). Adjusted multivariate regression analysis showed that the natural logarithm value of FGF23 level [ln(FGF23)] was positively associated with body mass index (rho = 0.002), serum phosphate level (rho = 0.0001), and negatively with eGFR (rho = 0.0006). Multivariate logistic regression analysis showed that vertebral fracture was independently associated with ln(FGF23) (adjusted odds ratio, 4.44; 95% confidence interval, 1.13-17.46). A receiver-operating-characteristic curve of ln(FGF23) showed that the optimal cutoff level of FGF23 indicative of vertebral fracture was 56.8 pg/ml (sensitivity, 0.82; specificity, 0.63). Conclusions: FGF23 level was independently associated with the levels of bone-metabolism-related markers and vertebral fracture. FGF23 is a new candidate marker for detecting abnormalities of bone metabolism and vertebral fracture in elderly CKD patients.