What is the primary function of sevelamer?

Sevelamer's primary function is to bind phosphate in the gastrointestinal tract, which helps to manage hyperphosphatemia, particularly in patients with chronic kidney disease (CKD) who cannot adequately eliminate phosphate. By binding phosphate, sevelamer prevents its absorption into the bloodstream, thereby reducing the serum phosphate levels. This is crucial because elevated phosphate levels can lead to vascular calcification and other complications in individuals with kidney failure.

The other potential answers highlight functions that are not relevant to sevelamer's mechanism of action. For example, increasing calcium absorption pertains more to medications or supplements that address calcium deficits rather than phosphate binding. Enhancing sodium retention is typically associated with different pharmacological agents that might be used for conditions like heart failure or low blood volume states and does not describe sevelamer’s action. Treating iron deficiency involves iron supplementation, which focuses on increasing iron levels in the body rather than managing phosphate levels.