Acute Hypercalcaemia: The Evidence Behind the Protocol

A 64-year-old man with carcinoma of the lung is brought in by his son. For two days he has been vomiting, and since this morning he has been drowsy and muddled. He has been constipated for a week. Earlier in the week, the son says, he was passing a lot of urine and was always thirsty. He weighs 60 kg. His tongue is dry. The report shows a total calcium of 14.6 mg/dL and an albumin of 3.0 g/dL. His renal function is normal. This is an illustrative case, not a real patient.

By the end of this article you will know why he is so dry, and what to give first. You will know why the strongest drug needs a bridge, and where else in India a high calcium comes from.

1. Correct the Calcium First

Part of the calcium in the blood is carried on albumin. When the albumin is low, the total calcium reads lower than the free calcium the patient is really living with. So the tool corrects it: corrected calcium = Ca + 0.8 x (4.0 - albumin). For him, that is 14.6 + 0.8 x (4.0 - 3.0) = 14.6 + 0.8 = 15.4 mg/dL.

The tool grades the corrected value: 10.6 to 12.0 mg/dL is mild, 12.1 to 14.0 moderate, 14.1 to 16.0 severe, and above 16.0 life-threatening. At 15.4 he is in the severe band, a hypercalcaemic crisis. His confusion and vomiting fit too. The old mnemonic still helps here: stones, bones, groans and psychiatric overtones. His constipation and nausea are the groans, and his muddle is the psychiatric overtone.

2. Which of the Two Causes?

Primary hyperparathyroidism and malignancy account for about 90% of all hypercalcaemia. The treatments have nothing in common, so separating the two is the early work. The parathyroid hormone (PTH) is the discriminator. If the PTH is high, or inappropriately normal for that calcium, the parathyroid is the source. If the PTH is suppressed, the parathyroid has done what it should, switched itself off, and the calcium is coming from somewhere else.

The tool asks you to send four tests together: PTH, PTHrP (the PTH-related peptide that some tumours make), 25-OH vitamin D and 1,25-dihydroxyvitamin D. In our patient, with a known cancer, a rapid rise and a calcium above 14, malignancy is the likely cause, and we expect a suppressed PTH. But the treatment of the crisis does not wait for those reports.

3. Why Is He So Dry?

“He has been passing a lot of urine. Surely his kidneys are working?” They are working, but against him. The tool explains that hypercalcaemia sets up a vicious cycle of dehydration, and it used to set out the four steps of that cycle:

• Calcium impairs renal concentrating ability (nephrogenic diabetes insipidus), causing polyuria.
• Hypercalcaemia causes nausea and vomiting, reducing fluid intake.
• Dehydration reduces GFR, decreasing renal calcium excretion.
• Higher serum calcium worsens symptoms further.

Read the four steps as a circle. A high calcium stops the kidney concentrating the urine, so water pours out; this is a nephrogenic diabetes insipidus. Vomiting stops water coming in. With less water in the circulation, the glomerular filtration rate (GFR) falls, and a kidney that filters less also gets rid of less calcium. So the calcium climbs further, and the vomiting and the polyuria get worse. Each turn of the circle makes the next one tighter.

That is why IV saline comes first. It breaks the cycle by restoring the GFR and promoting calciuresis, the loss of calcium in the urine. For the severe band, with normal renal function, the tool prints 0.9% saline at 200 to 300 mL/hour for the first 2 to 4 hours. Then it is 150 to 200 mL/hour, titrated to a urine output of 100 to 150 mL/hour. The goal is 4 to 6 litres in the first 24 hours. It gives the reason too: sodium and calcium travel together in the proximal tubule, so when the kidney passes sodium, it passes calcium with it. Saline only. Never a dextrose-containing fluid.

4. The Common Mistake: Reaching for Furosemide

Many of us were taught to give furosemide to “wash out” the calcium. It is easy to see why: a loop diuretic does make the kidney pass some calcium. But that calciuretic effect is small, and in a patient who is still dry the furosemide worsens the very dehydration that drives the cycle, and so drives the calcium up. A 2008 narrative review in the Annals of Internal Medicine called it an unproven yet common practice (reference 8). So the tool now says plainly: do not give a loop diuretic as part of the calcium-lowering plan. Keep it for the patient who becomes volume overloaded during rehydration, and give it then to make room for the saline, not to lower the calcium. The tool adds a related point: thiazide diuretics are contraindicated in hypercalcaemia, because they reduce the calcium the kidney passes.

5. The Strongest Drug Is the Slowest

Saline buys time, but on its own it will not hold the calcium down. The tool’s next step is a bisphosphonate: zoledronic acid (Zometa) 4 mg IV over 15 minutes, the most potent bisphosphonate available. Here is the sentence the tool used to give on how it works:

It inhibits osteoclast-mediated bone resorption.

Bone is not a fixed store. It is broken down and rebuilt all the time. The osteoclasts are the cells that break it down, and as they dissolve bone, they release its calcium into the blood. Many cancers drive the osteoclasts hard. A bisphosphonate stops them, so the calcium stops coming out at its source.

“Then why does it take so long?” Because it stops new resorption; it does not pull back the calcium already in the blood. Its onset is 2 to 4 days, with the peak effect at 4 to 7 days, and one dose lasts 2 to 4 weeks. That gap is why the tool adds calcitonin as a bridge. Salmon calcitonin works in 4 to 6 hours. The tool’s dose is 4 units/kg SC or IM every 12 hours, so for him 4 x 60 = 240 units every 12 hours. Check the strength of the vial in your hand before you draw it up, because Indian ampoules do not all carry the same strength.

“If calcitonin works in hours, why not use it alone?” Because it lowers the calcium by only 1 to 2 mg/dL. And its effect fades within 48 to 72 hours, as the body stops responding to it (tachyphylaxis). It is a bridge, not the treatment. Stop it after 48 hours.

Two more points from the tool. Pamidronate 60 to 90 mg IV is the cheaper alternative in many Indian hospitals. And a bisphosphonate is not given when the eGFR is below 30 or the creatinine above 4.5 mg/dL, because of its nephrotoxicity. Denosumab 120 mg SC takes its place: it is not cleared by the kidney, and its onset is also 2 to 4 days.

6. When the Calcium Comes From a Granuloma

In Indian hospitals, tuberculosis is an important and often overlooked cause of hypercalcaemia. “How can an infection raise the calcium?” The tool used to explain it in two sentences:

Activated macrophages in granulomata express 1-alpha hydroxylase, converting 25-OH vitamin D to active 1,25-dihydroxyvitamin D independently of PTH regulation. The result: unregulated calcium absorption.

In plain words: vitamin D has to be switched on before it works. Normally the last switch, 1-alpha hydroxylation, happens in the kidney, and PTH controls it. The macrophages in a granuloma carry the same switch, and nobody controls theirs. So they keep making active vitamin D, and the gut keeps absorbing calcium. That is why the tool asks for the 1,25-dihydroxyvitamin D, which will be high, and the PTH, which will be suppressed.

The treatment follows the mechanism. Corticosteroids, prednisolone 20 to 40 mg/day, rapidly reduce the production of active vitamin D and lower the calcium. The same picture is seen in sarcoidosis, granulomatosis with polyangiitis and fungal infections.

Back to Our Patient

His corrected calcium is 15.4 mg/dL: severe. He gets 0.9% saline at 200 to 300 mL/hour for the first few hours, then 150 to 200 mL/hour, with an hourly urine output and no furosemide. His renal function is normal, so he gets zoledronic acid 4 mg over 15 minutes. Calcitonin 240 units every 12 hours bridges the first 48 hours. His calcium is checked every 6 to 8 hours, and his ECG is watched on telemetry. The PTH comes back suppressed and the PTHrP raised. That is the humoral hypercalcaemia of malignancy, and the tool reminds us of one more thing: it lowers the calcium, not the cause. Until the cancer is treated, the calcium will come back.

Try This

A 32-year-old man has had three months of fever and weight loss, with enlarged hilar lymph nodes. His corrected calcium is 12.4 mg/dL. The PTH is suppressed, the PTHrP is normal, and the 1,25-dihydroxyvitamin D is high. What is happening, and what lowers the calcium? Illustrative case.

Answer. A suppressed PTH means the calcium is not coming from the parathyroid. A normal PTHrP makes the humoral hypercalcaemia of malignancy less likely. A high 1,25-dihydroxyvitamin D points to a granuloma making its own active vitamin D. In India, think of tuberculosis; sarcoidosis gives the same picture. He is in the moderate band, so hydrate him, and prednisolone 20 to 40 mg/day lowers the calcium, while the cause itself is diagnosed and treated.

Take-Home Points

• Correct the calcium for the albumin first: Ca + 0.8 x (4.0 - albumin).
• Send PTH, PTHrP, 25-OH vitamin D and 1,25-dihydroxyvitamin D together; a raised or inappropriately normal PTH means the parathyroid, a suppressed PTH means look elsewhere.
• Saline first: hypercalcaemia dehydrates, and dehydration raises the calcium. No furosemide for the calcium.
• Zoledronic acid is the strongest and the slowest; bridge with calcitonin for 48 hours, and use denosumab when the eGFR is below 30.
• A suppressed PTH with a high 1,25-dihydroxyvitamin D means a granuloma: in India, think of tuberculosis; prednisolone lowers the calcium.

The opposite problem is in Acute Hypocalcaemia: The Evidence Behind the Protocol. What a high or low calcium does to the ECG is in The QT Interval and the Electrolytes.

Declaration: the author built and maintains the tool. It is free to use. The figures in this article are those the tool carried on 5 November 2026, in its Evidence tab and in the plan it prints, each from the sources the tool names. The illustrative cases follow the tool’s rules; check the tool’s result for a real patient.

References

1. Minisola S, Pepe J, Piemonte S, Cipriani C. The diagnosis and management of hypercalcaemia. BMJ. 2015;350:h2723.
2. Rosner MH, Dalkin AC. Onco-nephrology: the pathophysiology and treatment of malignancy-associated hypercalcemia. Clin J Am Soc Nephrol. 2012;7(10):1722-1729.
3. Maier JD, Levine SN. Hypercalcemia in the Intensive Care Unit: A Review of Pathophysiology, Diagnosis, and Modern Therapy. J Intensive Care Med. 2015;30(5):235-252.
4. Walker MD, Shane E. Hypercalcemia: A Review. JAMA. 2022;328(16):1624-1636.
5. Sharma OP. Hypercalcemia in granulomatous disorders: a clinical review. Curr Opin Pulm Med. 2000;6(5):442-447.
6. Zagzag J, Hu MI, Fisher SB, Perrier ND. Hypercalcemia and cancer: differential diagnosis and treatment. CA Cancer J Clin. 2018;68(5):377-386.
7. Bilezikian JP, Khan AA, Silverberg SJ, et al. Evaluation and management of primary hyperparathyroidism: summary statement and guidelines from the Fifth International Workshop. J Bone Miner Res. 2022;37(11):2293-2314.
8. LeGrand SB, Leskuski D, Zama I. Narrative review: furosemide for hypercalcemia, an unproven yet common practice. Ann Intern Med. 2008;149(4):259-263.
9. Turner J, Gittoes N, Selby P; Society for Endocrinology Clinical Committee. Society for Endocrinology Endocrine Emergency Guidance: emergency management of acute hypocalcaemia in adult patients. Endocr Connect. 2016;5(5):G7-G8.