Fractional Excretion of Calcium Calculator

Calculate the fractional excretion of calcium (FECa) to help determine the cause of hypocalcemia. This calculator is useful for differentiating between renal calcium wasting and other causes of low calcium levels.

How to Use This Calculator

Enter the urine calcium value in mg/dL from a spot urine sample
Enter the serum creatinine value in mg/dL from blood work
Enter the serum calcium value in mg/dL from blood work
Enter the urine creatinine value in mg/dL from the same spot urine sample
Click Calculate to see the fractional excretion of calcium percentage and interpretation

Formula Used

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)

Example Calculation

Clinical Scenario:

A patient with hypocalcemia (low blood calcium) is being evaluated to determine if the cause is renal calcium wasting or decreased calcium intake/absorption.

Given:

Urine Calcium = 15 mg/dL
Serum Creatinine = 1.2 mg/dL
Serum Calcium = 7.5 mg/dL (low)
Urine Creatinine = 60 mg/dL

Calculation:

FECa (%) = (15 × 1.2) / (7.5 × 60) × 100 = 18 / 450 × 100 = 4%

Result: 4% - This elevated value suggests renal calcium wasting as the cause of hypocalcemia.

Why This Calculation Matters

Clinical Applications

Differentiating causes of hypocalcemia
Evaluating patients with suspected renal tubular disorders
Assessing calcium handling in kidney disease
Guiding treatment decisions for calcium disorders

Interpretation Guide

FECa < 1%: Suggests decreased calcium intake or absorption
FECa 1-2%: Borderline/indeterminate result
FECa > 2%: Suggests renal calcium wasting
Values may vary based on clinical context and medications

Common Mistakes & Tips

Ensure all values are in the same units (mg/dL) before calculating. Converting between different units (like mmol/L to mg/dL) can lead to errors if not done correctly. Always verify that laboratory values are in the expected units before input.

Certain medications (like thiazide diuretics, loop diuretics, and bisphosphonates) can significantly affect calcium excretion and alter FECa results. Always consider the patient's current medications when interpreting results.

Frequently Asked Questions

FECa is most useful when evaluating patients with unexplained hypocalcemia. It helps differentiate between renal calcium wasting and other causes like decreased intake, malabsorption, or shifts of calcium into bone or cells.

No, FECa can be calculated using a spot urine sample (single random sample) paired with blood values. This is because the formula uses the ratio of calcium to creatinine in both urine and serum, which corrects for urine concentration.

Elevated FECa (>2%) can be caused by conditions that increase renal calcium excretion, including hyperparathyroidism, distal renal tubular acidosis, loop diuretic use, and certain genetic disorders affecting calcium handling in the kidneys.

References & Disclaimer

Medical Disclaimer

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

References

StatPearls: Fractional Excretion of Calcium - A comprehensive review of FECa calculation and clinical interpretation
National Kidney Foundation: Fractional Excretion - Overview of fractional excretion calculations in nephrology
Medscape: Hypocalcemia Workup - Clinical approach to evaluating hypocalcemia including FECa

Accuracy Notice

This calculator provides an estimate based on the values entered. Laboratory methods and reference ranges may vary between institutions. Results should be interpreted in the context of the patient's overall clinical picture by a qualified healthcare professional.

About the Author

Kumaravel Madhavan

Web developer and data researcher creating accurate, easy-to-use calculators across health, finance, education, and construction and more. Works with subject-matter experts to ensure formulas meet trusted standards like WHO, NIH, and ISO.

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