Hyperphosphatemia and Kidney Outcomes in ADPKD

Serum phosphate levels tend to be lower in autosomal polycystic kidney disease (ADPKD) than in other kidney diseases. This can obscure the clinical significance of hyperphosphatemia. Kosaku Nitta, MD, PhD, and colleagues wanted to determine whether serum phosphate levels could predict kidney outcomes in patients with ADPKD. 

Their study included 235 patients with ADPKD who were not taking drugs to treat hyperphosphatemia. The researchers performed survival analysis for the renal outcome of a 50% reduction in estimated glomerular filtration rate (eGFR) or initiation of renal replacement therapy. 

Multivariable Cox regression analyses found that serum phosphate (1 mg/dL increase; hazard ratio [HR]=2.03; P<.0001) was a significant risk factor for kidney disease progression. Meanwhile, hyperphosphatemia (phosphate >3.5 mg/dL, HR=2.05; >4.0 mg/dL, HR = 1.90; >4.5 mg/dL, HR = 2.78; >5.0 mg/dL, HR = 27.22) was significantly associated with kidney prognosis. Kaplan–Meier analysis found significantly lower kidney survival rates in patients with phosphate >3.5 mg/dL than in those without hyperphosphatemia (log-rank test, P<.0001). Similar Kaplan–Meier analysis results occurred for >4.0 mg/dL, >4.5 mg/dL, and >5.0 mg/dL.  

The two-year kidney survival rate for ADPKD patients with phosphate >3.5 mg/dL was 66.7% overall and 41.4% in patients with stage 4–5 CKD. Patients with phosphate >4.0 mg/dL had a survival rate of 46.8% overall and 28.2% in stages 4–5 CKD. 

In summary, hyperphosphatemia was associated with kidney prognosis in patients with ADPKD. Even mildly elevated serum phosphate levels of >3.5 or >4.0 mg/dL should receive attention. 

Source: Clinical and Experimental Nephrology.