Hyperphosphatemia Is Associated with Kidney Prognosis in Patients with Autosomal Dominant Polycystic Kidney Disease

Background: The relationship between serum phosphate (P) levels and progression of kidney disease in patients with autosomal dominant polycystic kidney disease (ADPKD) remains unclear. Compared with other kidney disorders, patients with ADPKD typically have lower levels of serum P, potentially masking its clinical importance. This study sought to assess whether serum P levels can serve as a predictor of renal outcomes in ADPKD patients. Methods: We included 235 patients with ADPKD who were not taking drugs to treat hyperphosphatemia. Survival analysis was performed for the renal outcome of a 50% reduction in estimated glomerular filtration rate (eGFR) or initiation of renal replacement therapy. Results: The patients had mean age of 46 yeras, eGFR of 41.8 mL/min/1.73 m2, and total kidney volume (TKV) of 1254.0 mL. The median follow-up period was 10.4 years, and the renal outcome was observed in 116 patients. Multivariable Cox regression analyses revealed that serum P (1 mg/dL increase, HR=2.03, P<0.0001) was a significant risk factor associated with kidney disease progression. Similarly, hyperphosphatemia (P>4.0 mg/dL, HR=1.90, P=0.0157; P>4.5 mg/dL, HR=2.78, P=0.0047; P>5.0 mg/dL, HR=27.22, P<0.0001) was significantly associated with renal prognosis. Kaplan-Meier analysis showed that kidney survival rates were significantly lower in patients with P>3.5 mg/dL than in those without hyperphosphatemia (log-rank test, P<0.0001). The 2-year kidney survival rate of ADPKD patients with P>4.0 mg/dL was 46.8% in the entire cohort and 28.2% in patients with stage 4-5 CKD, indicating an extremely poor renal prognosis. Conclusion: Hyperphosphatemia was associated with renal prognosis in patients with ADPKD. In these patients, attention should be paid to even mild serum P elevation of P>3.5 or P>4.0 mg/dL.