Age- and sex-tailored serum phosphate thresholds do not improve cardiovascular risk estimation in CKD.

BACKGROUND: Disordered metabolism of phosphorus is one of the hallmarks of chronic kidney disease (CKD), resulting in increased cardiovascular morbidity and mortality. Age and sex may affect the metabolism of phosphorus and subsequently its serum level. We evaluated if age- and sex-specific cutoffs for hyperphosphatemia may define cardiovascular risk better than the current guideline cutoffs. METHODS: We used data from 16,834 subjects participating in the 1999-2006 National Health and Nutrition Examination Survey (NHANES); the prevalence of self-reported cardiovascular disease (CVD) and mortality rates were analyzed in CKD patients for both the classic definitions (CH; i.e., NKF-KDOQI and K-DIGO) and a tailored definition (TH) of hyperphosphatemia by means of regression models adjusted for age, sex, race/ethnicity, smoking status and body mass index. The cutoffs for TH were represented by the 95th percentile of an age- and sex-matched non-CKD population. RESULTS: Serum phosphorus levels showed an inverse correlation with age (r = -0.12; p<0.001); females showed higher levels than males (3.78 ± 0.54 mg/dL vs. 3.62 ± 0.58 mg/dL; p<0.001). Even if the association between the TH definition and CVD was marginally better compared with the CH definition (odds ratio [OR] = 1.49, 95% confidence interval [95% CI], 1.04-2.13; p=0.030 vs. OR=1.55, 95% CI, 0.98-2.44; p = 0.059), the TH model was not superior in predicting CVD or mortality. CONCLUSIONS: Our data suggest that a tailored, age- and sex-specific definition of hyperphosphatemia is not superior to conventional definitions in predicting cardiovascular events in patients with CKD.