Fractional Excretion of Calcium (FECa / Calcium–Creatinine Clearance Ratio)

What This Calculator Measures

Calculates the fractional excretion of calcium (calcium–creatinine clearance ratio, CCCR) to help distinguish familial hypocalciuric hypercalcemia (FHH) from primary hyperparathyroidism in PTH-dependent hypercalcemia.

How to Use

1. Use in patients with hypercalcemia and elevated or inappropriately normal PTH.
2. Collect spot urine calcium, urine creatinine, serum calcium, and serum creatinine at the same time.
3. Enter all four values and review the FECa and its category.
4. Consider CASR gene testing when the result is in the gray zone but FHH is suspected.

Interpretation Guide

A FECa below 1% (CCCR < 0.01) suggests FHH; 1–2% is a gray zone where some FHH patients fall; above 2% primary hyperparathyroidism is more likely. Low urine calcium also occurs with vitamin D deficiency, thiazides, lithium, and renal insufficiency.

Clinical Significance

FHH is caused by a reset calcium-sensing receptor with relative hypocalciuria despite hypercalcemia. The calcium–creatinine clearance ratio is a key discriminator that prevents unnecessary parathyroid surgery in FHH patients.

When to Use

• PTH-dependent hypercalcemia: FHH vs primary hyperparathyroidism
• Preoperative screening recommended by NICE before parathyroid surgery
• Family history of hypercalcemia

When Not to Use

• In hypercalcemia with suppressed PTH (malignancy, sarcoidosis)
• In vitamin D deficiency or low calcium intake, which lower urine calcium
• As the sole basis for genetic testing decisions

Limitations

• The 1% and 2% thresholds overlap clinically; up to ~20–35% of genetically confirmed FHH may have CCCR ≥ 0.01.
• Thiazides, lithium, vitamin D deficiency, and renal insufficiency lower urine calcium.
• CASR gene analysis remains the reference standard in ambiguous cases.

Worked Example

A 52-year-old woman with hypercalcemia has a urine calcium of 50 mg/dL, serum calcium 10 mg/dL, urine creatinine 100 mg/dL, and plasma creatinine 1.0 mg/dL.

FECa = (50 × 1.0) ÷ (10 × 100) × 100 = 5% (CCCR 0.05). Above 2%, primary hyperparathyroidism is more likely than FHH.

Evidence

Source

Original derivation + validation (peer-reviewed)

Reference

Christiansen C, et al. Discriminative power of three indices of renal calcium excretion for the distinction between familial hypocalciuric hypercalcaemia and primary hyperparathyroidism. Clin Endocrinol (Oxf). 2008;69(4):572-578.

Reviewed By

MedCalcHub Clinical Team

Version

1.0

Updated

2026-08

1. Christiansen C, et al. Clin Endocrinol (Oxf). 2008;69(4):572-578.
2. National Institute for Health and Care Excellence (NICE). Hyperparathyroidism (primary): diagnosis, assessment and initial management. NG132. 2019.

References

1. Christiansen C, et al. Discriminative power of three indices of renal calcium excretion for the distinction between familial hypocalciuric hypercalcaemia and primary hyperparathyroidism. Clin Endocrinol (Oxf). 2008;69(4):572-578. (Validation Study)
2. National Institute for Health and Care Excellence (NICE). Hyperparathyroidism (primary): diagnosis, assessment and initial management. NG132. 2019. (Guideline)

Frequently Asked Questions