Renal, Fluids, Electrolytes & Acid-Base · Topic 14 of 22

Hypercalcemia

Renal & electrolytes · calcium

Hypercalcemia

Correct for albumin, check PTH, and treat severe hypercalcemia with IV saline plus an antiresorptive — zoledronic acid or denosumab.

Key numbers

Total calcium above 10.4 mg/dLCa > 10.4 mg/dL

Denosumab or zoledronic acid 4 mg IVzoledronic acid 4 mg IV

Correct total calcium for albumin+0.8 per 1 g/dL albumin

01 · Defined byTotal calcium above 10.4 mg/dL

Hypercalcemia is total serum calcium above 10.4 mg/dL (normal 8.8–10.4) or ionized calcium above 5.2 mg/dL (1.30 mmol/L). Severity: mild 10.5–11.9, moderate 12.0–13.9, severe above 14 mg/dL.

02 · DoIV isotonic saline first

Significant hypercalcemia is nearly always hypovolemic: give isotonic saline first (often 1–2 L over the first hours unless heart failure limits it); add a loop diuretic only after volume is restored or for overload.

03 · GiveDenosumab or zoledronic acid 4 mg IV

For hypercalcemia of malignancy give an antiresorptive: denosumab 120 mg SC (Endocrine Society 2023 suggests it over an IV bisphosphonate) or zoledronic acid 4 mg IV once, which lowers calcium for weeks.

Causes & risk factors

Why it happens

Malignancy: PTHrP, bone lysis, calcitriolCancer raises calcium by PTH-related peptide (squamous cell lung, head and neck, renal, breast), osteolytic bone metastases or myeloma, or calcitriol (lymphoma). Calcium above 13 mg/dL with no obvious cause suggests cancer.

Drug causes: thiazides, lithium, vitamin DOther causes include thiazides, lithium, vitamin D toxicity, milk-alkali syndrome (calcium carbonate with alkalosis and AKI), granulomatous disease, thyrotoxicosis and immobilization; stop calcium, vitamin D and thiazides.

Presentation

What you'll see

Polyuria, constipation, stones, confusionSymptoms: polyuria and polydipsia (nephrogenic concentrating defect), constipation, nausea, abdominal pain, kidney stones, weakness, and above 12 mg/dL confusion, delirium, stupor or coma; it can cause AKI or nephrocalcinosis.

ECG: short QT intervalSevere hypercalcemia shortens the QTc and can cause arrhythmias, particularly in patients taking digoxin.

Diagnosis & monitoring

Work-up

Correct total calcium for albuminCorrected Ca = measured Ca + 0.8 × (4.0 − albumin). Measure ionized calcium when proteins are abnormal: low albumin can mask hypercalcemia, and myeloma paraprotein can mimic it.

Do right now

In this order

First moves

IV isotonic saline first

→

Calcitonin bridges the first 48 hours

→

Denosumab or zoledronic acid 4 mg IVzoledronic acid 4 mg IV

→

Check PTH first: high vs suppressed

Why each step

IV isotonic saline firstSignificant hypercalcemia is nearly always hypovolemic: give isotonic saline first (often 1–2 L over the first hours unless heart failure limits it); add a loop diuretic only after volume is restored or for overload.

Calcitonin bridges the first 48 hoursCalcitonin 4–8 IU/kg SC every 12 hours lowers calcium 1–2 mg/dL within hours but loses effect (tachyphylaxis) after about 48 hours; in severe hypercalcemia of malignancy start it together with an IV bisphosphonate or denosumab.

Denosumab or zoledronic acid 4 mg IVFor hypercalcemia of malignancy give an antiresorptive: denosumab 120 mg SC (Endocrine Society 2023 suggests it over an IV bisphosphonate) or zoledronic acid 4 mg IV once, which lowers calcium for weeks.

Check PTH first: high vs suppressedIntact PTH splits the work-up: high or inappropriately normal PTH means primary hyperparathyroidism (or familial hypocalciuric hypercalcemia); suppressed PTH (usually < 20 pg/mL) points to malignancy, vitamin D excess or granulomatous disease.

Management

Orders

Steroids for calcitriol-driven hypercalcemiaGlucocorticoids (prednisone 20–40 mg daily) lower calcitriol-mediated hypercalcemia — sarcoidosis and other granulomatous disease, some lymphomas, and vitamin D toxicity.

Hemodialysis for extreme levels or kidney failureUse hemodialysis with low-calcium dialysate for severe hypercalcemia (above about 18 mg/dL or with severe symptoms), especially with kidney failure, where saline and diuresis cannot work.

Symptomatic primary hyperparathyroidism: parathyroidectomyParathyroidectomy treats symptomatic or progressive primary hyperparathyroidism; asymptomatic criteria include calcium > 1 mg/dL above normal, CrCl < 60 mL/min, T-score ≤ −2.5, age < 50 or urine calcium > 400 mg/day.

Primary hyperparathyroidism or malignancy?

Commonly confused

PTH	High or inappropriately normal
Usual calcium	Rarely above 12 mg/dL; < 11 suggests it
Mediator	Parathyroid adenoma or hyperplasia
Typical setting	Outpatient, older woman, often asymptomatic
Definitive treatment	Parathyroidectomy

Commonly confused

Tell apart

Low urine calcium suggests FHH, not surgeryFamilial hypocalciuric hypercalcemia mimics mild primary hyperparathyroidism but has low 24-hour urine calcium (low fractional calcium excretion) and a family history; parathyroidectomy does not cure it.

More detail

Reference

Show 5 reference facts

Cinacalcet lowers PTH and calcium in primary hyperparathyroidism when surgery is not possible and is an option, with antiresorptives, for parathyroid carcinoma.

Repeated IV bisphosphonates can cause osteonecrosis of the jaw, and zoledronic acid is nephrotoxic; denosumab can cause hypocalcemia, so give calcium and vitamin D as needed.

Alternatives: pamidronate 60–90 mg IV once (not repeated within 7 days); denosumab 120 mg SC every 4 weeks with extra doses on days 8 and 15 — also the choice for hypercalcemia refractory to bisphosphonates.

Observed asymptomatic primary hyperparathyroidism: stay hydrated, avoid thiazides, and monitor calcium and renal function every 6 months and bone density yearly.

Treating the underlying cancer is what controls hypercalcemia of malignancy and prevents recurrence; antiresorptives only buy time.

Pearl

Saline for today, calcitonin for the first 48 hours, an antiresorptive for the weeks after — and PTH to tell you why.

Sources · Merck Manual Professional — Hypercalcemia (reviewed Jun 2025) · Merck Manual Professional — Overview of Disorders of Calcium Concentration · El-Hajj Fuleihan G et al. Treatment of Hypercalcemia of Malignancy in Adults: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab 2023;108:507–528 (abstract via Europe PMC) · Merck Manual Professional — Hypocalcemia (estimation of ionized calcium) · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).