DENVER—Higher serum phosphorus levels are associated with lower blood hemoglobin (Hb) levels and a greater likelihood of anemia in renal transplant recipients, a study found.

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“Our findings highlight an intriguing potential link between two common and clinically important complications seen in patients with kidney transplants and with CKD: mineral and bone disorders and anemia,” said lead investigator Csaba P. Kovesdy, MD, Associate Professor of Clinical Medicine at the University of Virginia in Charlottesville and Chief of Nephrology at Salem VA Medical Center in Salem, Va.

“While we cannot claim a causal relationship between higher phosphorus and lower hemoglobin based on an observational study, it is possible that, if such a causal effect exists, then lowering serum phosphorus could have benefits beyond those that we know about currently. Namely, it could be an additional way to treat post-transplant anemia.”

The study, which involved 992 renal transplant recipients, is the first to examine the effect of serum phosphorus on anemia in renal transplant patients. The researchers noted that the causes of post-transplant anemia include mechanisms common to those found in patients with CKD, such as erythropoietin deficiency, iron deficiency, inflammation, and oxidative stress. Other potential influences include transplant-specific factors such as acute rejection, drug effects, malignancy, and infection.

Study findings, which the researchers presented at the American Society of Nephrology’s Renal Week conference, revealed that higher serum phosphorus levels were associated with lower Hb levels. For example, patients with serum phosphorus levels below 2.8 mg/dL had a mean Hb level of more than 14 g/dL, whereas patients whose serum phosphorus levels were above 3.7 mg/dL had a mean Hb level of about 13 g/dL.

Additionally, Dr. Kovesdy and his colleagues found that a 0.8 mg/dL elevation in serum phosphorus level was associated with a 78% increased odds of post-transplant anemia after adjusting for age, gender, smoking status, diabetes, transplant vintage, history of acute rejection, estimated glomerular filtration rate, inflammatory markers, calcium levels, parathyroid hormone levels, iron levels, and other potential confounders. In adjusted analyses, a serum phosphate level above 3.7 mg/dL was associated with a fourfold increased odds of transplant anemia compared with a level below 2.8 mg/dL.

The association between higher serum phosphorus and lower Hb levels “was present throughout the normal concentration range of serum phosphorus, and could provide a potential explanation for the higher mortality associated with higher serum phosphorus even in individuals with no frank hyperphosphatemia,” the investigators concluded in their poster presentation.

In an interview with Renal & Urology News, Dr. Kovesdy observed: “Given the questionable benefits of anemia treatment using erythropoetin and its derivatives, it is important to uncover potential other therapeutic avenues to address this important complication. Before we can apply these findings in clinical practice, though, we will need prospective studies to test the causality of the link between phosphorus and anemia.”