Fractional Excretion of Calcium Calculator

The Fractional Excretion of Calcium Calculator estimates the percentage of filtered calcium excreted in urine based on urine and serum lab values. This tool helps medical professionals quickly diagnose the cause of hypocalcemia. Whether you are identifying renal calcium wasting, ruling out malabsorption, or evaluating kidney function, this calculator provides immediate insight into calcium handling.

Enter urine calcium value in mg/dL
Enter serum creatinine value in mg/dL
Enter serum calcium value in mg/dL
Enter urine creatinine value in mg/dL

How Fractional Excretion of Calcium Is Calculated

Fractional Excretion of Calcium (FECa) measures the percentage of filtered calcium that passes into the urine. This ratio helps doctors determine if the kidneys are wasting calcium or if the body is not absorbing enough.

FECa (%) = (Urine Calcium × Serum Creatinine) / (Serum Calcium × Urine Creatinine) × 100

Where:

  • Urine Calcium = Calcium concentration in urine (mg/dL)
  • Serum Creatinine = Creatinine concentration in blood (mg/dL)
  • Serum Calcium = Calcium concentration in blood (mg/dL)
  • Urine Creatinine = Creatinine concentration in urine (mg/dL)

To calculate this value, follow these steps:

  1. Multiply urine calcium by serum creatinine to account for kidney filtration rate.
  2. Multiply serum calcium by urine creatinine to standardize for urine concentration.
  3. Divide the first product by the second and multiply by 100.

This specific formula is the standard method in nephrology for assessing calcium handling accuracy.

What Your Fractional Excretion of Calcium Means

The FECa percentage reveals exactly how the kidneys are managing calcium levels in the body.

Renal Calcium Wasting (>2%)

If the result is above 2%, the kidneys are leaking too much calcium into the urine. This suggests renal tubular defects or high parathyroid hormone levels. Treatment focuses on correcting the underlying kidney dysfunction or using specific medications.

Appropriate Calcium Retention (<1%)

A result below 1% means the kidneys are holding onto calcium correctly. The low blood calcium is likely due to poor intake, low Vitamin D, or gut absorption issues. You should check the patient’s diet and supplement use.

Borderline Results (1-2%)

Results between 1% and 2% are unclear. Doctors must look at other lab tests and the patient’s history to determine the cause.

Important

Current medications, especially diuretics, can alter these results significantly. Always review the patient’s full medication list before interpreting the values.

This calculator is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

Monitor levels after stopping or starting diuretics to see the true baseline calcium handling.