Hypercalcemia is a condition of high calcium levels (total Ca2+> 10.5 mg/dL or ionized Ca2+> 5.25 mg/dL) in the blood serum. For information regarding the physiology and homeostasis of calcium, please see the article. The most common causes of hypercalcemia are primary hyperparathyroidism and malignancy with paraneoplastic production of parathyroid hormone-related protein (PTHrP). Symptoms of hypercalcemia include nephrolithiasis, bone pain, abdominal pain, and polyuria. Management depends on the severity of calcium imbalance. Mild and asymptomatic moderate hypercalcemia is treated with oral rehydration and low calcium intake, while symptomatic moderate cases and severe cases require IV rehydration and calcitonin administration. Hypercalcemic crisis is a life-threatening complication that manifests with dehydration, oliguria, and altered consciousness and requires immediate forced diuresis.
Hypercalcemia = total serum calcium concentration > 10.5 mg/dL (> 2.62 mmol/L), or ionized (free) calcium concentration > 5.25 mg/dL (> 1.31 mmol/L) 
|Types of hypercalcemia||Etiology||Pathophysiology|
|Non-PTH-mediated||Hypercalcemia of malignancy|| |
|Granulomatous disorders (e.g., )|
|Long periods of immobilization|| |
|of the bone|| |
Primary hyperparathyroidism and hypercalcemia of malignancy account for > 90% of cases of hypercalcemia. Compared to primary hyperparathyroidism, serum calcium is typically higher in hypercalcemia of malignancy (> 13 mg/dL, or > 3.25 mmol/L), and patients, therefore, exhibit more severe symptoms.
The clinical presentation is variable and may be asymptomatic.
- Nephrolithiasis, nephrocalcinosis (calcium oxalate > calcium phosphate stones)
- Bone pain; , arthralgias, myalgias, fractures
- Abdominal pain
- Nausea and vomiting
- Peptic ulcer disease 
- Neuropsychiatric symptoms such as anxiety, depression, fatigue, and cognitive dysfunction
- Diminished muscle excitability
- Cardiac arrhythmias
- Muscle weakness, paresis
- Polyuria and dehydration
- Hypercalcemic crisis: life-threatening condition that should be suspected at total calcium levels > 14 mg/dL (3.5 mmol/L) or ionized calcium > 10 mg/dL (2.5 mmol/L); patients present with
The presentation of hypercalcemia includes stones (nephrolithiasis), bones (bone pain, arthralgias), thrones (increased urinary frequency), groans (abdominal pain, nausea, vomiting), and psychiatric overtones (anxiety, depression, fatigue). Note that these are also the findings of vitamin D overdose!
Subtypes and variants
Familial hypocalciuric hypercalcemia (FHH) 
- Etiology: autosomal dominant inactivating mutation in the CaSR gene → decreased sensitivity of G-coupled calcium-sensing receptors in parathyroid glands and kidneys; → higher levels of Ca2+ required to suppress PTH and higher reabsorption of Ca2+ in the kidney → hypocalciuria with mild hypercalcemia and normal or increased PTH levels
- Clinical features
- Therapy: no treatment necessary
Evaluate calcium imbalance
- Initial test: serum calcium concentration
- Confirm true hypercalcemia: measure ionized calcium or use serum albumin to calculate corrected calcium.
- Differentiate between low PTH and high PTH: to determine the underlying cause of hypercalcemia
- Further tests
The corrected calcium concentration calculated using serum albumin may not be accurate when major pH changes have taken place in the body (e.g., following surgery). In these cases, it is better to measure ionized calcium directly.
PTH levels in hypercalcemia
|PTH level||Conditions||Laboratory findings|
|Low PTH||Hypercalcemia of malignancy|| |
|Vitamin D intoxication|
|High to normal PTH||Primary hyperparathyroidism|
|Familial hypocalciuric hypercalcemia (FHH)|| |
- Treatment of any underlying disorder (e.g., glucocorticoids in sarcoidosis or any other granulomatous disease → reduction in activity of mononuclear cells producing calcitriol)
- Mild or asymptomatic hypercalcemia: total calcium < 12 mg/dL (< 3 mmol/L) or ionized calcium < 8 mg/dL (< 2 mmol/L)
- Moderate hypercalcemia: total calcium 12–14 mg/dl (3–3.5 mmol/L)
Severe or symptomatic hypercalcemia: total calcium > 14 mg/dL (> 3.5 mmol/L) or ionized calcium > 10 mg/dL (> 2.5 mmol/L)
- Immediate therapy 
- Cause-based therapy
- Excessive bone resorption (e.g., hypercalcemia of malignancy, immobilization): bisphosphonates (zoledronic acid, pamidronate)
- Renal insufficiency or heart failure: loop diuretics (with monitoring of serum potassium) to avoid volume overload
- Dialysis in very severe cases (total calcium > 18 mg/dL; ionized calcium > 4.5 mmol/L) or concomitant renal failure