Relationship between serum phosphorus and mortality in non-dialysis chronic kidney disease patients: evidence from NHANES 2001–2018

Hyperphosphatemia is common in chronic kidney disease (CKD), associated with higher mortality in dialysis patients. Its impact in non-dialysis patients, especially those with preserved kidney function, remains uncertain.

A prospective cohort study was conducted using data from the National Health and Nutrition Examination Survey (2001–2008). Serum phosphorus was analyzed as a continuous variable, or categorized into three groups: < 3.5 mg/dL, 3.5 to < 4.5 mg/dL, and ≥ 4.5 mg/dL. Cox proportional hazards models were used to analyze the association between phosphorus with all-cause and cardiovascular disease (CVD) mortality, with or without adjustment for age, sex, race, hemoglobin, estimated glomerular filtration rate (eGFR), serum albumin, serum calcium, 25(OH)D, obesity, hypertension, diabetes, and CVD.

A total of 7694 participants were included in the analysis, representing 28 million CKD patients in the United States. During mean 92 months of follow up, 2708 all-cause deaths (including 969 CVD deaths) were observed. Per 1 mg/dL increase in phosphorus was associated with a 13% and 24% increased risk of all-cause mortality (hazard ratio [HR], 1.13; 95%CI, 1.02–1.24) and CVD mortality (HR, 1.24; 95%CI, 1.07–1.45), respectively. Compared with the < 3.5 mg/dL, phosphorus ≥ 4.5 mg/dL was associated with a 28% and 57% increased risk of all-cause mortality (HR, 1.28; 95%CI, 1.05–1.55) and CVD mortality (HR, 1.57; 95CI, 1.19–2.08), respectively. In participants with eGFR < 60 ml/min/1.73m², elevated phosphorus (≥ 4.5 mg/ dL) were significantly associated with increased risk of all-cause mortality (HR, 1.36; 95%CI, 1.07–1.72). No significant association was observed in eGFR ≥ 60 ml/min/1.73m² group (HR, 1.31; 95%CI, 0.86–1.99). This correlation does not differ significantly between subgroups defined by eGFR level (P for interaction = 0.889).

Serum phosphorus above 4.5 mg/dL is significantly associated with a 28% and 57% increased risk of all-cause and CVD death in non-dialysis CKD patients, respectively. This relationship still demonstrated in patients with eGFR < 60 ml/min/1.73m². However, for population with eGFR ≥ 60 ml/min/1.73m², further verification is needed.