Hypercalcaemia (Adult Master Topic)

1. Overview

Hypercalcaemia is a common and potentially life-threatening electrolyte disturbance defined by a corrected serum calcium concentration > 2.6 mmol/L. It is a major clinical challenge, affecting ~1-3% of hospital inpatients and serving as a critical diagnostic clue for underlying malignancy or primary hyperparathyroidism. [1]

The clinical significance of hypercalcaemia is defined by its metabolic and neuromuscular toxicity. While mild elevations are often asymptomatic, severe hypercalcaemia (> 3.5 mmol/L) can precipitate acute renal failure, coma, and fatal cardiac arrhythmias. Pathophysiologically, it is the result of an imbalance between calcium entry into the extracellular fluid (via gut absorption or bone resorption) and its exit (via renal excretion or bone deposition). [2]

Management has been refined by the use of Zoledronic Acid, Denosumab for refractory malignancy cases, and the 2024 standards for volume resuscitation using Balanced Crystalloids. Diagnostic gold standards prioritize the PTH-mediated vs. PTH-independent algorithm to efficiently reach a definitive diagnosis. [3]

2. Epidemiology

The Two Pillars of Aetiology

• Primary Hyperparathyroidism (PHP): Accounts for 90% of cases in the outpatient setting. Most common in postmenopausal women.
• Malignancy-Associated Hypercalcaemia (MAH): Accounts for 65-90% of cases in the inpatient setting. This carries a poor prognosis (median survival less than 3-6 months). [4]

Causes and Mechanisms

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3. Aetiology & Pathophysiology

⚠️ THE 7-STEP MOLECULAR MECHANISM

1. CaSR Inactivation/Bypass: In primary HPT, the Calcium-Sensing Receptor (CaSR) in the parathyroid glands is "reset" or bypassed, leading to autonomous PTH release despite high systemic calcium.
2. PTHrP Mimicry: In malignancy, tumours release PTH-related Protein (PTHrP). Its N-terminal sequence is homologous to PTH, allowing it to bind to the PTH-1 receptor in bone and kidney.
3. RANKL Over-expression: PTH or PTHrP binds to osteoblasts, causing them to over-express RANK-Ligand.
4. Osteoclast Storm: RANKL binds to the RANK receptor on osteoclast precursors, leading to massive activation and bone resorption, dumping Calcium and Phosphate into the blood.
5. Renal Reabsorption Shift: PTH/PTHrP acts on the distal tubule to increase calcium reabsorption and on the proximal tubule to inhibit phosphate reabsorption (Phosphaturia).
6. Nephrogenic Diabetes Insipidus (NDI): High calcium inhibits Aquaporin-2 expression in the collecting duct. This causes a water-diuresis (Polyuria), leading to severe dehydration and a fall in GFR.
7. The Hypercalcaemic Death-Spiral: Dehydration reduces renal calcium clearance. As calcium rises further, it induces vomiting (more fluid loss) and worsens NDI, leading to rapid metabolic collapse. [5, 6, 7]

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4. Clinical Presentation

The "Classic" Mnemonic

• Stones: Renal calculi and nephrocalcinosis.
• Bones: Aching bone pain and fragility fractures.
• Groans: Constipation, nausea, and acute pancreatitis.
• Moans: Depression, "Brain fog," and in severe cases, frank psychosis or coma.

Physical Signs

1. Dehydration: Reduced skin turgor and dry mucous membranes.
2. Muscle Weakness: Proximal myopathy (common in PHP).
3. ECG Signs: Shortened QT interval (the hallmark). Bradycardia and first-degree heart block may also be present. [8]

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5. Investigations: The PTH Branch Point

Step 1: Corrected Calcium

Always correct for albumin: Corrected Ca = Measured Ca + 0.02 x (40 - Albumin).

Step 2: The PTH Assay

• High/Inappropriate PTH: Suggests Primary Hyperparathyroidism. (Next step: 24h Urine Calcium to exclude FHH).
• Suppressed PTH: Suggests Malignancy, Vitamin D excess, or Sarcoidosis. (Next step: PTHrP, Myeloma screen, and CXR).

The FHH Clue: CCCR

Familial Hypocalciuric Hypercalcaemia (FHH) is a benign condition caused by a loss-of-function mutation in the CaSR.

• CCCR (Calcium:Creatinine Clearance Ratio):
  • less than 0.01: Highly suggestive of FHH. (Do NOT perform surgery).
  • > 0.02: Suggests Primary HPT. [9]

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6. Management: The Emergency Protocol

1. Volume Expansion (The Priority)

• Fluid: 3–6 Litres of 0.9% NaCl or Balanced Crystalloid over 24 hours.
• Rationale: Restores GFR and promotes Calciuresis (Sodium and Calcium are co-excreted in the proximal tubule).

2. Bisphosphonates (The Bone Shield)

• Agent: Zoledronic Acid 4mg IV (or Pamidronate 60-90mg).
• Caveat: Takes 48-72 hours to reach maximal effect. Do not repeat doses within 7 days.

3. Second-line / Refractory

• Denosumab: Anti-RANKL monoclonal antibody; effective in bisphosphonate-refractory malignancy cases.
• Calcitonin: Rapid onset (hours) but exhibits Tachyphylaxis (stops working after 48h). Useful as a "bridge" in severe crisis.
• Steroids: IV Hydrocortisone or Oral Prednisolone; highly effective for Vitamin D-mediated hypercalcaemia (Sarcoid/Lymphoma). [10, 11]

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7. Evidence: Landmark Trials

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8. Single Best Answer (SBA) Questions

Question 1

A 70-year-old male is admitted with confusion and a corrected calcium of 3.8 mmol/L. His PTH is suppressed (less than 1.0 pmol/L). He has a 40 pack-year smoking history. What is the most likely molecular driver of his hypercalcaemia?

• A) Autonomous secretion of PTH from a parathyroid adenoma
• B) Activation of the Wnt/β-catenin pathway
• C) Secretion of PTH-related Protein (PTHrP)
• D) Ectopic production of 1,25-dihydroxyvitamin D
• E) Inactivation of the Calcium-Sensing Receptor (CaSR)
• Answer: C. In a smoker with severe hypercalcaemia and suppressed PTH, a squamous cell carcinoma of the lung secreting PTHrP is the most likely cause (Humoral Hypercalcaemia of Malignancy).

Question 2

A 35-year-old female is found to have a mild hypercalcaemia (2.75 mmol/L) on routine screening. Her PTH is inappropriately normal (5.5 pmol/L). Her father and brother also have mild high calcium. Her 24-hour urine calcium is very low. What is the most appropriate management?

• A) Urgent Parathyroidectomy
• B) Start Cinacalcet 30mg BD
• C) Intravenous Zoledronic Acid
• D) Reassurance and avoid surgery
• E) Neck Ultrasound and Sestamibi scan
• Answer: D. This is classic Familial Hypocalciuric Hypercalcaemia (FHH). It is a benign genetic condition (CaSR mutation). Surgery is ineffective and unnecessary.

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9. Viva Scenario: The "Sarcoid" Shift

Examiner: "Your patient has severe hypercalcaemia due to Sarcoidosis. Why is their 1,25-dihydroxyvitamin D high even if their PTH is suppressed?"

Candidate:

1. Mechanism: In sarcoidosis, the Alveolar Macrophages within the granulomas express the enzyme 1-α-hydroxylase autonomously.
2. Dysregulation: Unlike the kidney, where this enzyme is tightly regulated by PTH, the macrophage expression is unregulated.
3. Result: They convert 25-OH Vit D into the active 1,25-(OH)2 Vit D regardless of systemic calcium levels.
4. Management: I would treat this with Glucocorticoids (Prednisolone), which directly inhibit the 1-α-hydroxylase activity in the macrophages. [12]

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10. Patient Explanation

"Hypercalcaemia means the calcium level in your blood is too high. Calcium is usually a 'good' mineral for bones, but when too much of it leaks into the blood, it acts like a poison to your kidneys and brain. This is why you've felt thirsty and confused. We are treating you with lots of IV fluids to 'flush' the calcium out and a specific 'bone-strengthening' medicine to lock the calcium back into your skeleton where it belongs."

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11. References

1. Minisola S, et al. The diagnosis and management of hypercalcaemia. BMJ. 2015. [PMID: 26037642]
2. Bilezikian JP, et al. Guidelines for the Management of Asymptomatic Primary Hyperparathyroidism. J Clin Endocrinol Metab. 2014. [PMID: 25162665]
3. Major P, et al. Zoledronic acid is superior to pamidronate in the treatment of hypercalcemia of malignancy. J Clin Oncol. 2001. [PMID: 11157036]
4. Hu MI, et al. Denosumab for treatment of hypercalcemia of malignancy. J Clin Endocrinol Metab. 2014. [PMID: 24915119]
5. Shane E, Berenson JR. Treatment of hypercalcemia. UpToDate. 2024.

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Last Updated: 2026-01-05 | MedVellum Editorial Team