Fractional Excretion of Calcium (FECa)
What is Fractional Excretion of Calcium?
The Fractional Excretion of Calcium (FECa) is a clinical calculation used primarily to differentiate between Familial Hypocalciuric Hypercalcemia (FHH) and Primary Hyperparathyroidism (PHPT) in patients presenting with elevated blood calcium levels.
This ratio measures how much calcium is excreted in the urine relative to the amount filtered by the kidneys. Since FHH is caused by a sensing defect in the kidneys that leads them to reabsorb too much calcium, patients with FHH will have very low calcium in their urine despite high levels in their blood.
The FECa Formula
The calculation requires four variables measured from blood (serum) and a spot urine sample:
FECa = [(Urine Calcium × Serum Creatinine) / (Serum Calcium × Urine Creatinine)]
Note: If you wish to express this as a percentage, multiply the result by 100.
How to Interpret Results
| FECa Result | Likely Diagnosis |
|---|---|
| Less than 0.01 (1%) | Suggests Familial Hypocalciuric Hypercalcemia (FHH) |
| 0.01 to 0.02 (1% – 2%) | Indeterminate / Gray Zone |
| Greater than 0.02 (2%) | Suggests Primary Hyperparathyroidism (PHPT) |
Example Calculation
If a patient has a Serum Calcium of 11.0 mg/dL, Serum Creatinine of 1.0 mg/dL, Urine Calcium of 4.0 mg/dL, and Urine Creatinine of 80 mg/dL:
- (4.0 × 1.0) = 4
- (11.0 × 80) = 880
- 4 / 880 = 0.0045 (or 0.45%)
This result is below 0.01, which strongly points towards FHH rather than PHPT.