High Calcium: How Do Doctors Tell FHH1 From Cancer?
At a Glance
Doctors differentiate FHH1 from cancer by measuring Parathyroid Hormone (PTH) levels in the blood. In cancer, high calcium causes PTH levels to drop near zero. In benign FHH1, PTH remains normal or elevated. A 24-hour urine test and CASR genetic testing then confirm FHH1.
In this answer
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Finding “high calcium” on a routine blood test can be alarming, as many patients immediately worry about cancer. However, doctors can usually tell the difference between cancer and benign conditions like Familial Hypocalciuric Hypercalcemia type 1 (FHH1) very quickly using a simple blood test for Parathyroid Hormone (PTH).
In benign conditions like FHH1 or Primary Hyperparathyroidism (PHPT), your body’s calcium thermostat is set too high, so your PTH levels remain normal or slightly elevated even when your calcium is high [1][2]. In contrast, when cancer causes high calcium, the body’s thermostat works correctly and tries to fix the problem by shutting down normal PTH production completely [3][2][4]. By looking at your PTH levels, doctors can confidently rule out cancer and point the investigation toward benign parathyroid conditions.
The Body’s Calcium Thermostat
To understand how doctors differentiate these conditions, it helps to know how the body regulates calcium. Your parathyroid glands (four tiny glands in your neck) act like a thermostat. When calcium is low, they release PTH to raise it. When calcium is high, they are supposed to turn off and stop making PTH.
When doctors find high calcium in your blood, their very first step is to measure your PTH levels [2][5]. This splits high calcium into two distinct categories:
- PTH-Dependent (Thermostat is altered): If your calcium is high but your PTH is normal or elevated, your parathyroid glands are inappropriately continuing to work [1][2]. The most common cause is a benign condition called Primary Hyperparathyroidism (PHPT). FHH1 is a rarer genetic condition that falls into this same category and often looks identical to PHPT on initial blood tests [6][7].
- PTH-Independent (Thermostat is turned off): If your calcium is high and your PTH is nearly zero (suppressed), it means something else in your body is driving the calcium up, and your parathyroid glands have shut down to try to stop it [2][4]. Cancer-related high calcium falls into this category [8][9].
How Doctors Identify Cancer-Related High Calcium
Hypercalcemia of malignancy (cancer-related high calcium) is almost always PTH-independent [4]. This usually happens in one of two ways. Most commonly, cancers produce a rogue protein called PTHrP (Parathyroid Hormone-related Protein) [10][8]. This protein mimics PTH, forcing the bones to release calcium into the blood. In other cases, cancers that have spread directly to the bones (bone metastases) cause calcium to be released as the bone breaks down.
If a doctor suspects cancer, they will look at your blood work. In hypercalcemia of malignancy:
- Normal PTH is suppressed (close to zero) [3][11][9].
- If your doctor tests for it, the rogue protein PTHrP may be significantly elevated [12][13][3].
Furthermore, high calcium caused by cancer is rarely a surprise finding in someone who feels otherwise healthy. It typically occurs in advanced stages of known cancers.
How Doctors Confirm FHH1
FHH1 is a benign (harmless), lifelong genetic condition caused by a mutation in the CASR gene, which stands for calcium-sensing receptor [14][15][16]. Because this receptor is altered, your body believes it needs more calcium than it actually does.
If your PTH is normal or slightly elevated alongside high calcium (meaning cancer is highly unlikely), doctors will take specific steps to confirm FHH1:
- 24-Hour Urine Test: Doctors will ask you to collect your urine for a full day to measure the calcium-to-creatinine clearance ratio (CCCR) [17][18][19]. Creatinine is simply a normal muscle waste product used to measure how concentrated your urine is. In FHH1, the kidneys hold onto calcium, resulting in unusually low levels of calcium in the urine [14][6][7]. A CCCR under 0.01 strongly suggests FHH1, while a ratio above 0.02 usually points to Primary Hyperparathyroidism [20][21][22].
- Genetic Testing: Because urine tests can sometimes be inconclusive or overlap with other parathyroid conditions, a genetic test of the CASR gene is the definitive way to prove you have FHH1 [23][24][16].
- Family History: Since FHH1 is genetic, doctors will often ask if anyone else in your family has high calcium or if anyone has had unsuccessful parathyroid surgeries. If you are diagnosed with FHH1, your doctor may suggest that your close relatives get their calcium checked.
The most important takeaway is that FHH1 and cancer have completely different biochemical fingerprints. A simple look at your PTH level provides immense reassurance and guides your medical team down the correct diagnostic path.
Common questions in this guide
How does a PTH blood test help rule out cancer?
What is the 24-hour urine test used for in diagnosing FHH1?
Is genetic testing required to diagnose FHH1?
Why do doctors ask about my family history if my calcium is high?
Questions to Ask Your Doctor
Curated prompts to bring to your next appointment.
- 1.What was my intact PTH level, and does it clearly point away from cancer?
- 2.Have we performed a 24-hour urine collection to calculate my calcium-to-creatinine clearance ratio (CCCR)?
- 3.What is my exact CCCR, and does it fall clearly into the FHH1 range or is it borderline with primary hyperparathyroidism?
- 4.Do you recommend genetic testing of the CASR gene to definitively confirm FHH1?
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References
References (24)
- 1
Pathophysiology of Hypercalcemia.
Goltzman D
Endocrinology and metabolism clinics of North America 2021; (50(4)):591-607 doi:10.1016/j.ecl.2021.07.008.
PMID: 34774236 - 2
[Hypercalcemia - Diagnosis and Management].
Koster M, Brändle M
Praxis 2022; (111(12)):675-681 doi:10.1024/1661-8157/a003888.
PMID: 36102025 - 3
Two cases of humoral hypercalcemia of malignancy complicating infantile fibrosarcoma.
Hirschfeld R, Welch JJG, Harrison DJ, et al.
Pediatric blood & cancer 2017; (64(10)) doi:10.1002/pbc.26511.
PMID: 28371408 - 4
Sudden onset of parathyroid hormone-independent severe hypercalcemia from reversal of tumoral calcinosis in a dialysis patient.
Kamar FB, Mann B, Kline G
BMC nephrology 2016; (17(1)):137 doi:10.1186/s12882-016-0355-y.
PMID: 27683096 - 5
Clinical Profile and Outcomes of Patients With Hypercalcemia in an Indian Tertiary Care Center.
Sukhija T, Midha V, Mittal N, et al.
Cureus 2023; (15(9)):e46062 doi:10.7759/cureus.46062.
PMID: 37900460 - 6
Familial hypocalciuric hypercalcemia and related disorders.
Lee JY, Shoback DM
Best practice & research. Clinical endocrinology & metabolism 2018; (32(5)):609-619 doi:10.1016/j.beem.2018.05.004.
PMID: 30449544 - 7
Efficacy of calcium excretion and calcium/creatinine clearance ratio in the differential diagnosis of familial hypocalciuric hypercalcemia and primary hyperparathyroidism.
Bhangu JS, Selberherr A, Brammen L, et al.
Head & neck 2019; (41(5)):1372-1378 doi:10.1002/hed.25568.
PMID: 30554440 - 8
Hypercalcemia of Malignancy: Mechanisms and Therapeutic Implications of Concurrently Elevated PTHrP and Calcitriol.
Kometas ML, Maalouf NM
Journal of the Endocrine Society 2025; (9(9)):bvaf104 doi:10.1210/jendso/bvaf104.
PMID: 40662114 - 9
Hypercalcemia of Malignancy: Simultaneous Elevation in Parathyroid Hormone-Related Peptide and 1,25 Dihydroxyvitamin D in Sarcoma.
Kim DW, Miller A, Li A, et al.
AACE clinical case reports 2021; (7(3)):169-173 doi:10.1016/j.aace.2020.11.037.
PMID: 34095480 - 10
Hypercalcemia in Cancer: Causes, Effects, and Treatment Strategies.
Bartkiewicz P, Kunachowicz D, Filipski M, et al.
Cells 2024; (13(12)) doi:10.3390/cells13121051.
PMID: 38920679 - 11
Metabolic Bone Disease in the Context of Metastatic Neuroendocrine Tumor: Differentiation from Skeletal Metastasis, the Molecular PET-CT Imaging Features, and Exploring the Possible Etiopathologies Including Parathyroid Adenoma (MEN1) and Paraneoplastic Humoral Hypercalcemia of Malignancy Due to PTHrP Hypersecretion.
Ranade R, Basu S
World journal of nuclear medicine 2017; (16(1)):62-67 doi:10.4103/1450-1147.172307.
PMID: 28217023 - 12
Hypercalcemia of malignancy in metastatic esophageal squamous cell carcinoma with simultaneous PTHrP and calcitriol overproduction: A case report with literature review.
Song R, Bijay Y, Rizk SH, Cao S
Annals of medicine and surgery (2012) 2021; (68()):102667 doi:10.1016/j.amsu.2021.102667.
PMID: 34401137 - 13
Incidence of humoral hypercalcemia of malignancy among hypercalcemic patients with cancer.
Szymanski JJ, Otrock ZK, Patel KK, Scott MG
Clinica chimica acta; international journal of clinical chemistry 2016; (453()):190-3.
PMID: 26706788 - 14
A novel homozygous mutation of the calcium-sensing receptor gene associated with apparent autosomal recessive inheritance of familial hypocalciuric hypercalcemia.
Li N, Li X, Ni XL, et al.
Chinese medical journal 2021; (134(15)):1869-1871 doi:10.1097/CM9.0000000000001568.
PMID: 34397587 - 15
A clinical perspective of parathyroid hormone related hypercalcaemia.
Han CH, Fry CH, Sharma P, Han TS
Reviews in endocrine & metabolic disorders 2020; (21(1)):77-88 doi:10.1007/s11154-019-09529-5.
PMID: 31797261 - 16
A case of familial hypocalciuric hypercalcemia type 1 due to CASR p.Pro55Leu mutation.
Sumida A, Iizuka K, Kato T, et al.
BMC endocrine disorders 2022; (22(1)):164 doi:10.1186/s12902-022-01077-5.
PMID: 35733207 - 17
Is routine 24-hour urine calcium measurement useful during the evaluation of primary hyperparathyroidism?
Li SR, McCoy KL, Levitt HE, et al.
Surgery 2022; (171(1)):17-22 doi:10.1016/j.surg.2021.04.055.
PMID: 34325903 - 18
Genetics of hereditary forms of primary hyperparathyroidism.
English KA, Lines KE, Thakker RV
Hormones (Athens, Greece) 2024; (23(1)):3-14 doi:10.1007/s42000-023-00508-9.
PMID: 38038882 - 19
Clinical and molecular characterization of familial hypocalciuric hypercalcemia in an endocrine practice: a case series of 25 patients.
Lin J, Wang TS, Donahue A, Shaker JL
JBMR plus 2026; (10(5)):ziag049 doi:10.1093/jbmrpl/ziag049.
PMID: 42038813 - 20
CALCIUM CREATININE CLEARANCE RATIO IS NOT HELPFUL IN DIFFERENTIATING PRIMARY HYPERPARATHYROIDISM FROM FAMILIAL HERPERCALCEMIC HYPOCALCIURIA: A STUDY OF 1000 PATIENTS.
Moore EC, Berber E, Jin J, et al.
Endocrine practice : official journal of the American College of Endocrinology and the American Association of Clinical Endocrinologists 2018; doi:10.4158/EP-2018-0350.
PMID: 30289313 - 21
Genetic testing for hereditary hyperparathyroidism and familial hypocalciuric hypercalcaemia in a large UK cohort.
Mariathasan S, Andrews KA, Thompson E, et al.
Clinical endocrinology 2020; (93(4)):409-418 doi:10.1111/cen.14254.
PMID: 32430905 - 22
Excluding familial hypocalciuric hypercalcaemia before surgery for primary hyperparathyroidism - a practical evaluation of urinary calcium using a retrospective cohort design.
McAllister J, Arshad MF, Rab E, Balasubramanian SP
Annals of the Royal College of Surgeons of England 2022; (104(9)):710-716 doi:10.1308/rcsann.2021.0333.
PMID: 35446160 - 23
Identification of a novel large CASR deletion in a patient with familial hypocalciuric hypercalcemia.
García-Castaño A, Madariaga L, Azriel S, et al.
Endocrinology, diabetes & metabolism case reports 2018; (2018()).
PMID: 30530875 - 24
Familial hypocalciuric hypercalcemia in an index male: grey zones of the differential diagnosis from primary hyperparathyroidism in a 13-year clinical follow up.
Zajíčková K, Dvořáková M, Moravcová J, et al.
Physiological research 2020; (69(Suppl 2)):S321-S328 doi:10.33549/physiolres.934522.
PMID: 33094630
This page explains the biochemical differences between FHH1 and cancer for educational purposes. Always consult your endocrinologist or primary care physician to interpret your specific calcium and PTH blood test results.
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