Calcium Creatinine Clearance Ratio Calculator

Calcium Creatinine Clearance Ratio Calculator for Endocrinology. A CCCR below 0.01 makes FHH substantially more likely and should trigger CASR (and where relevant GNA11/AP2S1) genetic testing plus screening of first-degree relatives before any parathyroid surgery. A ratio above 0.02 favors PHPT with hypercalciuria and is reassuring for surgical work-up. The 0.01 to 0.02 zone is genuinely indeterminate: roughly 20 to 25 percent of genetically confirmed FHH patients fall in or above it, and the ratio alone cannot exclude FHH. Treat the number as a probability shifter that directs further testing, not a standalone diagnosis; in one surgical cohort CCCR sensitivity for FHH was only about 64 percent.

How this calculator works

The calcium/creatinine clearance ratio (CCCR) expresses renal calcium handling relative to creatinine and is computed as (urine calcium x serum creatinine) / (serum calcium x urine creatinine), using calcium and creatinine measured in consistent units on paired serum and urine samples. It is a dimensionless fractional clearance that removes the need for a timed collection because urine volume and time cancel out. A 24-hour collection is preferred, but a fasting spot urine paired with a simultaneous serum sample gives a usable estimate. The result quantifies how avidly the kidney reabsorbs filtered calcium.

When to use this calculator

Use CCCR in a patient with PTH-dependent (non-suppressed PTH) hypercalcemia to separate primary hyperparathyroidism (PHPT) from familial hypocalciuric hypercalcemia (FHH), a benign CaSR-inactivating disorder that does not benefit from parathyroidectomy. It is the standard biochemical screen before referring for parathyroid surgery. Do not apply it when PTH is suppressed (malignancy, vitamin D toxicity), and interpret cautiously in vitamin D deficiency, low dietary calcium, thiazide or lithium use, pregnancy, or an eGFR below roughly 60 mL/min, all of which lower calcium excretion and can mimic FHH.

Inputs used

  • Urine calcium
  • Serum calcium
  • Urine creatinine
  • Serum creatinine

Clinical interpretation

A CCCR below 0.01 makes FHH substantially more likely and should trigger CASR (and where relevant GNA11/AP2S1) genetic testing plus screening of first-degree relatives before any parathyroid surgery. A ratio above 0.02 favors PHPT with hypercalciuria and is reassuring for surgical work-up. The 0.01 to 0.02 zone is genuinely indeterminate: roughly 20 to 25 percent of genetically confirmed FHH patients fall in or above it, and the ratio alone cannot exclude FHH. Treat the number as a probability shifter that directs further testing, not a standalone diagnosis; in one surgical cohort CCCR sensitivity for FHH was only about 64 percent.

Worked example

A woman with calcium 2.70 mmol/L and non-suppressed PTH has a 24-hour urine calcium of 1.8 mmol/L with urine creatinine 6.0 mmol/L and serum creatinine 70 micromol/L (0.070 mmol/L). CCCR = (1.8 x 0.070) / (2.70 x 6.0) = 0.126 / 16.2 = 0.0078, i.e. below 0.01. This points toward FHH, so CASR sequencing and a family calcium screen are warranted before considering surgery, rather than proceeding to parathyroidectomy.

Limitations and safety notes

The ratio's central weakness is overlap: a meaningful minority of FHH patients have CCCR above 0.01 and some PHPT patients (especially with concurrent vitamin D deficiency or reduced GFR) fall below it, so the single cutoff neither confirms nor excludes either diagnosis. Vitamin D repletion before testing is essential because deficiency depresses calciuria. The measure is unreliable in chronic kidney disease, on thiazides or lithium, in pregnancy, and in FHH type 3 (AP2S1), which can present with higher ratios. A borderline or low result mandates genetic confirmation rather than a change in surgical plan on its own.

Frequently asked questions

What CCCR value suggests familial hypocalciuric hypercalcemia?

A ratio below 0.01 raises suspicion for FHH and should prompt CASR genetic testing and family screening. A value above 0.02 favors primary hyperparathyroidism. Values between 0.01 and 0.02 are indeterminate and do not resolve the diagnosis on their own.

Can I use a spot urine instead of a 24-hour collection?

Yes. Because urine volume and collection time cancel in the ratio, a fasting spot urine paired with a simultaneous serum sample is acceptable, though a 24-hour collection remains preferred and lets you also report absolute calcium excretion.

Why can vitamin D deficiency cause a misleadingly low ratio?

Low vitamin D reduces intestinal calcium absorption and renal calcium excretion, lowering the CCCR and mimicking FHH. Repleting vitamin D before measurement reduces false-positive low ratios in true PHPT.

Does a low CCCR mean the patient should not have parathyroid surgery?

Not by itself. A low ratio raises FHH probability and should redirect work-up toward CASR/GNA11/AP2S1 sequencing and relative screening, but genetic confirmation, not the ratio alone, should determine whether surgery is inappropriate.

Does the ratio work when PTH is suppressed?

No. CCCR is only meaningful in PTH-dependent hypercalcemia. If PTH is suppressed, the differential is malignancy, vitamin D excess, or other non-parathyroid causes, and the ratio does not apply.

References

  • Marx SJ, Attie MF, Stock JL, Spiegel AM, Levine MA. Maximal urine-concentrating ability: familial hypocalciuric hypercalcemia versus typical primary hyperparathyroidism. J Clin Endocrinol Metab. 1981. PMID: 6259192.
  • Bhangu JS, Selberherr A, Brammen L, Scheuba C, Riss P. Efficacy of calcium excretion and calcium/creatinine clearance ratio in the differential diagnosis of familial hypocalciuric hypercalcemia and primary hyperparathyroidism. Head Neck. 2019. PMID: 30554440.
  • Bilezikian JP, Khan AA, Silverberg SJ, et al. Evaluation and Management of Primary Hyperparathyroidism: Summary Statement and Guidelines from the Fifth International Workshop. J Bone Miner Res. 2022. PMID: 36245251.

Editorial review and citation methodology

Reviewed by the Quick Medical Calculator Editorial Team. Last reviewed: June 7, 2026. The review checks calculator inputs, intended population, interpretation, limitations, and source alignment.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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