The urinary phosphate to serum fibroblast growth factor 23 ratio is a useful marker of atherosclerosis in early-stage chronic kidney disease

Background: Fibroblast growth factor 23 (FGF23) regulates mineral homeostasis. In developed renal dysfunction, FGF23 levels increase to maintain the phosphate excretion capacity. However, in diabetic patients with early-stage renal impairment, the FGF23 elevation is not very sensitive. We hypothesized that urinary phosphate (U-P)/serum FGF23 ratio would theoretically be an index that reflects the number of nephrons (nephron index). In this study, we determined whether the nephron index would be associated with renal function and vascular diseases in diabetic patients. Methods: In total, 142 patients with diabetes mellitus were enrolled. The nephron index was calculated using the following formula: U-P (mg/day)/ serum FGF23 (pg/ml). Results: The mean age was 63 ± 11 years and eGFR levels were 79.5 ± 25.4 ml/min/1.73 m², respectively. Thirty patients had a medical history of macroangiopathy. The Nephron index was significantly decreased in subjects with macroangiopathy compared with those without macroangiopathy. A multivariate analysis of risk factors for macroangiopathy revealed that duration of diabetes, eGFR, and nephron index were significantly associated with a higher frequency of arteriosclerotic disease. Conclusion: These findings suggest that a decrease in nephron index reflects early-stage renal impairment and is an independent risk factor of macroangiopathy in diabetic patients.