Fractional excretion of phosphate (FePO4)

Where:

• \( \text{Urine PO₄} \): The phosphate concentration in the urine (mg/dL or mmol/L).
• \( \text{Plasma Creatinine} \): The creatinine concentration in the plasma (mg/dL or µmol/L).
• \( \text{Plasma PO₄} \): The phosphate concentration in the plasma (mg/dL or mmol/L).
• \( \text{Urine Creatinine} \): The creatinine concentration in the urine (mg/dL or µmol/L).

Description:

The Fractional Excretion of Phosphate (FePO₄) is used to assess the renal handling of phosphate. It helps to determine whether the kidneys are excreting phosphate appropriately relative to the filtered load. This measurement is important in diagnosing conditions that affect phosphate metabolism, such as hypophosphatemia, chronic kidney disease, and tubular disorders.

Formula Explanation:

The formula calculates the fractional excretion of phosphate by comparing the ratio of phosphate in urine and plasma with the corresponding ratio for creatinine. This comparison gives an indication of the kidney's ability to excrete phosphate relative to the filtration rate of creatinine.

Interpretation:

• FePO₄ < 5%: Suggests a reduced excretion of phosphate, often seen in hypophosphatemia, and indicates that the kidneys are conserving phosphate.
• FePO₄ > 10%: Indicates an excessive excretion of phosphate, which may be seen in conditions like acute tubular necrosis or Fanconi syndrome.

Usage:

This calculator is particularly useful in assessing phosphate wasting disorders, kidney function, and phosphate balance in patients with renal issues or disorders related to phosphate metabolism.