What calcium level is dangerously high?

A total serum calcium above 14 mg/dL (3.5 mmol/L) is considered a hypercalcemic crisis and requires emergency treatment. Levels of 12–14 mg/dL (3.0–3.5 mmol/L) are moderately severe and often symptomatic. Severe hypercalcemia can cause cardiac arrhythmias, altered mental status, renal failure, and coma. Immediate treatment includes aggressive IV normal saline hydration, calcitonin, and often bisphosphonates or denosumab.

What is the difference between total and ionized calcium?

Total calcium measures all three fractions: protein-bound (about 40%, mainly albumin), complexed with anions like phosphate and citrate (about 10%), and ionized or free calcium (about 50%). Ionized calcium is the physiologically active form that affects neuromuscular function, cardiac contractility, and enzyme activity. When albumin is abnormal, total calcium may be misleading — corrected calcium or direct ionized calcium measurement should be used.

Why do you correct calcium for albumin?

About 40% of total serum calcium is bound to albumin. In hypoalbuminemia (common in hospitalized patients, liver disease, nephrotic syndrome), total calcium appears falsely low even though the physiologically active ionized calcium may be normal. The correction formula — Corrected Ca = Measured Ca + 0.8 × (4.0 − Albumin) — adjusts total calcium for albumin levels below 4.0 g/dL. When possible, measuring ionized calcium directly is more accurate.

What causes high calcium in blood?

The two most common causes of hypercalcemia account for about 90% of cases: primary hyperparathyroidism (most common in outpatients) and malignancy (most common in hospitalized patients). Malignancy-related hypercalcemia occurs via PTHrP secretion (lung, renal cell, breast cancers), osteolytic bone metastases (breast cancer, multiple myeloma), or excess 1,25-dihydroxyvitamin D production (lymphomas). Other causes include vitamin D toxicity, thiazide diuretics, sarcoidosis and other granulomatous diseases, immobilization, milk-alkali syndrome, and thyrotoxicosis.

What calcium level requires treatment?

Treatment urgency depends on the calcium level and symptoms. Mild hypercalcemia (10.5–12 mg/dL) in an asymptomatic patient may be monitored and evaluated without urgent treatment. Moderate hypercalcemia (12–14 mg/dL) typically requires IV hydration and further workup. Severe hypercalcemia (>14 mg/dL) or any symptomatic hypercalcemia is a medical emergency requiring aggressive IV saline, calcitonin, and often bisphosphonates. For hypocalcemia, symptomatic patients (tetany, seizures, QT prolongation) require IV calcium gluconate regardless of the absolute level.

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A comprehensive reference on serum calcium — normal ranges for total and ionized calcium, causes of hypercalcemia and hypocalcemia, when to correct for albumin, and clinical interpretation.

Normal Calcium Range — Quick Reference

Total Ca: 8.5–10.5 mg/dL (2.12–2.62 mmol/L)

Ionized Ca: 4.65–5.25 mg/dL (1.16–1.31 mmol/L)

Always correct total calcium for albumin if albumin <4.0 g/dL

What Is Serum Calcium?

Calcium is the most abundant mineral in the body, with approximately 99% stored in bones and teeth. The remaining 1% circulates in blood and is tightly regulated by parathyroid hormone (PTH), vitamin D, and calcitonin. Serum calcium is essential for neuromuscular function, cardiac contractility, coagulation, enzyme activity, and intracellular signaling.¹

Total serum calcium exists in three fractions: approximately 40% is bound to proteins (primarily albumin), 10% is complexed with anions such as phosphate, citrate, and bicarbonate, and 50% circulates as ionized (free) calcium. Only the ionized fraction is physiologically active. Because protein-bound calcium fluctuates with albumin levels, total calcium can be misleading in patients with hypoalbuminemia — a common scenario in hospitalized patients.²

Serum calcium is one of the most commonly ordered laboratory tests and is part of the comprehensive metabolic panel (CMP). Abnormalities in calcium — either hypercalcemia or hypocalcemia — can have significant clinical consequences and require systematic evaluation.

Calcium Normal Range

Reference ranges may vary slightly between laboratories. The values below reflect commonly used adult reference intervals:

Test	Conventional Units	SI Units	Notes
Total calcium (adult)	8.5–10.5 mg/dL	2.12–2.62 mmol/L	Correct for albumin if <4.0 g/dL
Ionized calcium (adult)	4.65–5.25 mg/dL	1.16–1.31 mmol/L	Physiologically active fraction; preferred in critically ill
Total calcium (neonates)	7.6–10.4 mg/dL	1.90–2.60 mmol/L	Lower range normal in first 48–72 hours of life
Total calcium (children)	8.8–10.8 mg/dL	2.20–2.70 mmol/L	Slightly higher range due to growth

Hypercalcemia Severity Classification

Severity	Total Ca (mg/dL)	Total Ca (mmol/L)	Typical Management
Mild	10.5–12.0	2.62–3.00	Outpatient workup; hydration
Moderate	12.0–14.0	3.00–3.50	IV saline hydration; often inpatient
Severe / Crisis	>14.0	>3.50	Emergency — aggressive IV saline, calcitonin, bisphosphonates

Conversion: mg/dL × 0.25 = mmol/L. These classifications use corrected calcium values.

What Does a High Calcium Level Mean? (Hypercalcemia)

Hypercalcemia is defined as a corrected total calcium >10.5 mg/dL (2.62 mmol/L). Two conditions account for approximately 90% of cases:³

Common Causes of Hypercalcemia

Primary hyperparathyroidism — The #1 cause in outpatients. Usually due to a single parathyroid adenoma (85%). Characterized by elevated PTH with high or high-normal calcium. Often mildly elevated and discovered incidentally.³
Malignancy — The #1 cause in hospitalized patients. Mechanisms include:
- Humoral hypercalcemia of malignancy (HHM) — PTHrP secretion (squamous cell lung cancer, renal cell, breast)
- Osteolytic metastases — Direct bone destruction (breast cancer, multiple myeloma)
- Excess 1,25-(OH)₂D production — Lymphomas (Hodgkin and non-Hodgkin)
Vitamin D toxicity — Exogenous vitamin D supplementation (usually >10,000 IU/day chronically)
Thiazide diuretics — Decrease renal calcium excretion; can unmask primary hyperparathyroidism
Granulomatous diseases — Sarcoidosis, tuberculosis, histoplasmosis (macrophages produce 1,25-vitamin D)
Immobilization — Particularly in patients with high bone turnover (Paget disease, adolescents)
Milk-alkali syndrome — Excessive calcium and absorbable alkali ingestion

Symptoms of Hypercalcemia

Classic mnemonic: "Stones, bones, abdominal moans, and psychic groans"

Stones — Nephrolithiasis, nephrocalcinosis
Bones — Bone pain, osteoporosis, osteitis fibrosa cystica
Abdominal moans — Nausea, vomiting, constipation, pancreatitis, peptic ulcer disease
Psychic groans — Confusion, lethargy, depression, coma
Other — Polyuria, polydipsia, shortened QT interval, arrhythmias

What Does a Low Calcium Level Mean? (Hypocalcemia)

Hypocalcemia is defined as a corrected total calcium <8.5 mg/dL (2.12 mmol/L) or ionized calcium <4.65 mg/dL (1.16 mmol/L). Always confirm with ionized calcium or albumin correction before diagnosing true hypocalcemia.⁴

Common Causes of Hypocalcemia

Hypoparathyroidism — Most commonly post-surgical (thyroidectomy, parathyroidectomy). Also autoimmune, infiltrative, or congenital (DiGeorge syndrome).⁴
Vitamin D deficiency — Inadequate intake, malabsorption, limited sun exposure, liver or kidney disease (impaired hydroxylation)
Chronic kidney disease (CKD) — Decreased 1,25-(OH)₂D production, hyperphosphatemia, skeletal resistance to PTH
Hypomagnesemia — Magnesium <1.0 mg/dL impairs PTH secretion and causes end-organ resistance to PTH. Calcium will not correct until magnesium is repleted.⁵
Acute pancreatitis — Calcium sequestration by saponification of fatty acids in the inflamed pancreatic bed
Massive transfusion — Citrate in blood products chelates ionized calcium
Hyperphosphatemia — Calcium-phosphate precipitation (tumor lysis syndrome, rhabdomyolysis, CKD)
"Hungry bone" syndrome — Rapid bone uptake of calcium after parathyroidectomy for severe hyperparathyroidism

Symptoms of Hypocalcemia

Perioral and distal extremity paresthesias (earliest symptom)
Muscle cramps, carpopedal spasm, tetany
Chvostek sign — Tapping facial nerve causes ipsilateral facial muscle twitching
Trousseau sign — BP cuff inflation above systolic for 3 minutes causes carpal spasm (more specific)
Prolonged QT interval, cardiac arrhythmias
Seizures (in severe hypocalcemia)
Laryngospasm, bronchospasm (rare but life-threatening)

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Klinische Praxistipps

🔑 Wichtige Hinweise

The mnemonic for the hypercalcemia workup: Check PTH first. If PTH is elevated → primary hyperparathyroidism (or familial hypocalciuric hypercalcemia). If PTH is suppressed → malignancy, vitamin D excess, or granulomatous disease.
Primary hyperparathyroidism and malignancy together account for ~90% of all hypercalcemia cases. The clinical context usually distinguishes them: PHPT is chronic and mild; malignancy-associated hypercalcemia is usually acute, severe, and the patient is clearly unwell.³
Albumin correction formula: Corrected Ca = Measured Ca + 0.8 × (4.0 − Albumin). This is an approximation — use our calculator or measure ionized calcium when precision matters.
Hypocalcemia will not correct until hypomagnesemia is treated. Always check and replete magnesium.
Alkalosis shifts calcium onto albumin binding sites, decreasing ionized calcium. Hyperventilating patients may develop symptomatic hypocalcemia (carpopedal spasm) even with normal total calcium.
ECG changes: Hypercalcemia shortens the QT interval. Hypocalcemia prolongs the QT interval. Severe hypercalcemia can cause Osborn (J) waves.
In the ICU, measure ionized calcium directly — corrected calcium formulas are unreliable in critical illness due to altered albumin binding, acid-base changes, and acute-phase responses.

Test Methodology

Total calcium is measured by colorimetric assay (arsenazo III or o-cresolphthalein). Ionized calcium is measured by ion-selective electrode on an arterial or venous blood gas analyzer. The specimen for ionized calcium must be processed anaerobically (exposure to air raises pH, which decreases ionized calcium).

Specimen Requirements

Total calcium: serum (gold-top or SST tube). No fasting required, though some sources recommend fasting for consistency. Ionized calcium: heparinized whole blood (blood gas syringe), processed promptly without air exposure. Tourniquet time should be minimized as prolonged venous stasis can falsely elevate total calcium.

Referenzen

Burtis CA, Ashwood ER, Bruns DE, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018.
Bushinsky DA, Monk RD. Electrolyte quintet: Calcium. Lancet. 1998;352(9124):306–311. doi:10.1016/S0140-6736(97)12331-5
Carroll MF, Schade DS. A practical approach to hypercalcemia. Am Fam Physician. 2003;67(9):1959–1966.
Cooper MS, Gittoes NJL. Diagnosis and management of hypocalcaemia. BMJ. 2008;336(7656):1298–1302. doi:10.1136/bmj.39582.589433.BE
Agus ZS. Hypomagnesemia. J Am Soc Nephrol. 1999;10(7):1616–1622. doi:10.1681/ASN.V1071616
Payne RB, Little AJ, Williams RB, Milner JR. Interpretation of serum calcium in patients with abnormal serum proteins. BMJ. 1973;4(5893):643–646.
Walker MD, Silverberg SJ. Primary hyperparathyroidism. Nat Rev Endocrinol. 2018;14(2):115–125. doi:10.1038/nrendo.2017.104

Referenzen zuletzt überprüft: Februar 2026