In a patient with PTH-dependent hypercalcemia, the CCCR helps separate Familial Hypocalciuric Hypercalcemia (FHH) — a benign inherited condition where the kidney reabsorbs calcium avidly — from Primary Hyperparathyroidism (PHPT). Enter paired serum and urine values (ideally from a 24-hour urine collection).
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Calcium-Creatinine Clearance Ratio
Formula: CCCR = (Urine Ca × Serum Cr) ÷ (Serum Ca × Urine Cr) Both calcium values must share the same units, and both creatinine values must share the same units — the result is a unitless ratio identical in conventional or SI units.
Interpretation (in PTH-dependent hypercalcemia):
• < 0.01 → suggests FHH — consider CASR genetic testing before parathyroid surgery
• > 0.02 → favors Primary Hyperparathyroidism
• 0.01–0.02 → indeterminate "grey zone" — correlate with family history, vitamin D, and genetics
Reading the result
CCCR is a screening aid, not a diagnosis on its own.
A low ratio (<0.01) is most useful for flagging possible FHH so that a patient isn't sent to unnecessary parathyroid surgery. Confounders can lower the ratio independently of FHH — vitamin D deficiency, low calcium/dairy intake, thiazide diuretics, lithium, and chronic kidney disease. Roughly 1 in 5 patients with genetically confirmed FHH have a ratio above 0.01, and some patients with PHPT fall below it, so a grey-zone or discordant result should prompt CASR (and related) genetic testing and a careful family history rather than reliance on the ratio alone. First-degree relatives with hypercalcemia, or onset before age 30 with a benign course, raise suspicion for FHH.
⚕️ Clinical note: This calculator is a decision-support aid for clinicians and informed patients and does not replace specialist evaluation. Distinguishing FHH from primary hyperparathyroidism has major management implications (FHH generally needs no surgery). Confirmed or suspected FHH warrants genetic counseling. Interpret every result in full clinical context with your endocrinologist.