The Fractional Excretion of Phosphate (FEP) calculator is an essential tool for evaluating renal phosphate handling, particularly in patients with hypophosphatemia. Under normal physiological conditions, the kidneys should conserve phosphate when plasma levels are low. This calculator assists clinicians in determining whether phosphate losses are occurring through the kidneys or other routes.
In patients with hypophosphatemia:
An FEP above 20% indicates renal phosphate wasting, suggesting that the kidneys are inappropriately excreting phosphate despite low serum levels.
An FEP below 20% usually points to an extrarenal source of phosphate loss, such as dietary insufficiency or gastrointestinal losses.
Studies have shown that in hypophosphatemic patients, those with extrarenal causes of phosphate depletion typically have lower FEP values, while those with renal phosphate loss exhibit higher FEP values, indicating inappropriate renal excretion.
