Hypercalcaemia

Overview

Hypercalcaemia is defined as an elevated serum calcium level above the upper limit of normal:

• Total Serum Calcium: > 2.60 mmol/L (corrected for serum albumin).
• Ionised Calcium (Physiologically Active): > 1.30 mmol/L.

Severity Cut-Offs (Corrected Total Calcium):

• Mild: 2.60–3.00 mmol/L (often asymptomatic or mild constipation/fatigue).
• Moderate: 3.00–3.50 mmol/L.
• Severe (“Hypercalcaemic Crisis”): > 3.50 mmol/L (high risk of cardiac arrhythmias, acute encephalopathy, and renal failure).

Primary Hyperparathyroidism (outpatient) and Malignancy (inpatient) account for > 90% of all clinical cases.

Approach

Step 1: Emergency Triage & Red Flag Screening (Hypercalcaemic Crisis)

• Serum Corrected Calcium > 3.50 mmol/L OR Severe Symptoms:
  • Neurological: Severe confusion, lethargy, obtundation, coma.
  • Cardiovascular: Shortened QTc interval, bradycardia, AV block, cardiac arrest.
  • Renal / Fluid: Severe dehydration (nephrogenic diabetes insipidus), acute kidney injury, oliguria.
  • Gastrointestinal: Intractable vomiting, acute pancreatitis, severe abdominal pain.

Step 2: Diagnostic Branching Logic (Parathyroid Hormone [PTH] Driven)

• Obtain 12-Lead ECG, spot urine/blood gas, and Intact PTH (iPTH).
• iPTH Elevated or Inappropriately Normal (>= 2.0 pmol/L):
  • -> PTH-Dependent Hypercalcaemia (Primary Hyperparathyroidism, Tertiary Hyperparathyroidism, Familial Hypocalciuric Hypercalcaemia [FHH]).
• iPTH Suppressed (< 1.5–2.0 pmol/L):
  • -> PTH-Independent Hypercalcaemia (Malignancy, Granulomatous disease, Vitamin D toxicity, Medications, Endocrine disorders).

Step 3: Branching Path for Suppressed PTH (Malignancy vs Non-Malignancy)

• Measure PTH-related Protein (PTHrP), 25-OH Vitamin D, 1,25-(OH)2 Vitamin D (Calcitriol), and Serum Protein Electrophoresis / Free Light Chains.

Differential Diagnosis

PTH-Dependent Causes (Inappropriately High / Normal PTH):

• Primary Hyperparathyroidism (PHPT – ~80% outpatient cases):
  • Distinguishing features: Solitary parathyroid adenoma (85%), hyperplasia (15%), or parathyroid carcinoma (<1%). Asymptomatic hypercalcaemia, elevated/normal PTH, low/normal serum phosphate, high 24h urinary calcium excretion (> 5 mmol/24h).
• Familial Hypocalciuric Hypercalcaemia (FHH):
  • Distinguishing features: Autosomal dominant inactivating mutation of Calcium-Sensing Receptor (CaSR). Asymptomatic, mild hypercalcaemia, inappropriately normal PTH, but low 24h urinary calcium excretion (< 2.5 mmol/24h) and Urinary Calcium-to-Creatinine Clearance Ratio (CCCR) < 0.01.
• Tertiary Hyperparathyroidism:
  • Distinguishing features: Seen in end-stage kidney disease (ESKD) with longstanding secondary hyperparathyroidism leading to autonomous parathyroid hyperplasia.

PTH-Independent Causes (Suppressed PTH – High-Risk Inpatient):

• Malignancy-Associated Hypercalcaemia (~80% inpatient cases):
  • Humoral Hypercalcaemia of Malignancy (HHM): Tumor secretion of PTHrP (Squamous cell carcinomas of lung/head & neck, renal cell carcinoma, bladder cancer).
  • Osteolytic Metastases: Direct bone breakdown by osteoclast activation (Breast cancer, Multiple Myeloma, Prostate cancer). Elevated Serum Free Light Chains / SPEP + lytic lesions on skeletal survey.
  • Tumor-Mediated 1,25-(OH)2 Vitamin D Production: Lymphomas.
• Granulomatous Disorders (Excess 1-alpha Hydroxylase Activity):
  • Distinguishing features: Sarcoidosis, Tuberculosis, Histoplasmosis, Beryllium toxicity. Macrophages autonomously convert 25-OH Vit D to active 1,25-(OH)2 Vit D (Calcitriol). Elevated ACE level, bilateral hilar lymphadenopathy on CXR.
• Medications / Exogenous Ingestion:
  • Thiazide Diuretics: Reduce renal calcium excretion; unmasks underlying primary hyperparathyroidism.
  • Lithium: Shifts CaSR set-point, raising PTH.
  • Milk-Alkali Syndrome: Excessive calcium carbonate ingestion (antacids) causing hypercalcaemia, metabolic alkalosis, and AKI.
  • Vitamin D / Vitamin A Toxicity.
• Thyrotoxicosis & Immobilization:
  • Increased bone turnover; common in severe hyperthyroidism or prolonged bed rest in young patients with high bone turnover.

Investigations

First-Line / Bedside & Emergency Diagnostics:

• 12-Lead ECG: Look for shortened QTc interval (classic), Osborne/J waves, prolonged PR interval, widened QRS, or cardiac conduction block.
• Serum Biochemistry: Corrected Total Calcium, Ionised Calcium, Phosphate (low in PHPT, high in Vit D excess/renal failure), Magnesium, Potassium, Urea, Creatinine (AKI screening).
• Intact PTH (iPTH): Key initial branching step to distinguish parathyroid vs non-parathyroid mechanisms.
• Blood Gas (ABG/VBG): Assess direct ionised calcium and acid-base status (alkalosis worsens symptoms; acidosis increases ionised fraction).

Targeted / Diagnostic Etiology Workup:

• 24-Hour Urinary Calcium & Creatinine Excretion: Mandatory to calculate Calcium-to-Creatinine Clearance Ratio (CCCR) to rule out FHH before parathyroid surgery.
• Secondary PTH-Suppressed Panel:
  • PTHrP: Elevated in Humoral Hypercalcaemia of Malignancy.
  • 25-OH Vitamin D & 1,25-(OH)2 Vitamin D: Differentiates nutritional Vit D toxicity (high 25-OH) from Granulomatous disease/Lymphoma (high 1,25-(OH)2).
  • Serum & Urine Protein Electrophoresis (SPEP/UPEP) + Free Light Chains: Screen for Multiple Myeloma.
  • Serum ACE & Chest X-Ray / CT: Screen for Sarcoidosis / Tuberculosis.
• Parathyroid Localization Imaging (For Surgery Planning in PHPT):
  • Neck Ultrasound + Technetium-99m Sestamibi SPECT-CT / 4D-CT: Identifies precise location of parathyroid adenomas.

Critical Management

Emergency Management of Moderate-to-Severe Hypercalcaemia (Ca2+ > 3.00–3.50 mmol/L):

• Step 1: Aggressive Isotonic Fluid Resuscitation (CORNERSTONE):
  • 0.9% Normal Saline IV at 200–500 mL/hr (target urine output > 100–150 mL/hr). Rehydrates the patient and promotes calciuresis by increasing sodium delivery to the proximal tubule.
• Step 2: Antiresorptive Therapy (Bisphosphonates):
  • IV Zoledronic Acid 4 mg IV over 15 minutes (or Pamidronate 60–90 mg IV over 2–4 hours).
  • Onset: Takes 24–48 hours to take effect, peak effect at 4–7 days. Adjust dose/use caution in severe renal impairment (eGFR < 30 mL/min).
• Step 3: Rapid Bridging Therapy (Immediate Onset):
  • Calcitonin 4–8 IU/kg SC/IM every 12 hours: Rapid onset within 2–4 hours (inhibits osteoclasts and promotes renal excretion). Useful as a bridge while waiting for Zoledronic acid to work. Note: Limited by tachyphylaxis (loses efficacy after 48 hours).
• Step 4: Targeted Therapies for Specific Etiologies:
  • Granulomatous Disease / Lymphoma / Vit D Toxicity / Myeloma: IV Hydrocortisone 100 mg q6h OR Oral Prednisolone 40–60 mg daily (inhibits 1-alpha hydroxylase activity and intestinal calcium absorption).
  • Severe Renal Impairment (eGFR < 30 mL/min) / Refractory to Bisphosphonates: Denosumab 120 mg SC (RANKL inhibitor).
• Step 5: Refractory / Life-Threatening Hypercalcaemia:
  • Hemodialysis with Low/Zero-Calcium Dialysate: Indicated in oliguric renal failure, severe heart failure, or calcium > 4.50 mmol/L.

References

1. Walsh J, Gittoes N, Selby P, Society for Endocrinology Clinical Committee. Society for Endocrinology endocrine emergency guidance: emergency management of acute hypercalcaemia in adult patients. Endocr Connect. 2016;5(5):G9-G11. doi:10.1530/EC-16-0055
2. Endocrine Society. Hypercalcemia guideline resources [Internet]. 2022 [cited 2026 Aug 20]. Available from: https://www.endocrine.org/clinical-practice-guidelines/hypercalcemia