Association of Serum Phosphorus Level With Anemia in Kidney Transplant Recipients

Background. Anemia and mineral and bone disorders (MBD) are both important and common complications in kidney transplant recipients. Studies in patients with chronic kidney disease indicated a possible independent association of higher serum phosphorus with anemia, but similar associations have not been examined in kidney transplant recipients. We hypothesized that higher serum phosphorus is associated with anemia independent of other components of MBD. Methods. We examined the association of serum phosphorus with hemoglobin level and the prevalence of anemia in a prevalent cohort of 992 kidney transplant recipients in a single outpatient transplant center. Associations were examined in linear and logistic regression models with adjustment for demographic and comorbid conditions for various known risk factors of anemia, including measures of iron deficiency, inflammation, and components of MB Dincluding serum levels of 25(OH) vitamin D, parathyroid hormone, and fibroblast growth factor 23. Results. In multivariable adjusted regression models, a 1 standard deviation (0.8 mg/dL) higher serum phosphorus level was associated with 0.26 g/dL lower blood hemoglobin concentration (95% confidence intervals -0.36 to -0.15, P < 0.001) and with an odds ratio for anemia of 1.77 (95% confidence intervals 1.33-2.37, P < 0.001). These associations were consistent across the entire spectrum of the physiologic serum phosphorus concentration and were more accentuated in patients with lower estimated glomerular filtration rate. Conclusions. Higher serum phosphorus is independently associated with anemia in kidney transplant recipients.