High Calcium Levels Explained
What hypercalcaemia means in your blood test, the PTH connection, and when to worry — written for Australian patients by health data analysts.
What Is Calcium and Why Is It Tested?
Calcium is the most abundant mineral in your body. About 99% is stored in bones and teeth, with the remaining 1% circulating in blood. That tiny circulating fraction is tightly regulated because it controls muscle contraction, nerve signalling, blood clotting, and heart rhythm.
Your body maintains blood calcium within a narrow range using three hormones: parathyroid hormone (PTH) raises calcium by pulling it from bones; calcitonin lowers calcium; and active vitamin D increases calcium absorption from the gut. When this system malfunctions, calcium levels rise or fall.
Calcium Ranges and Types of Measurement
Australian pathology labs measure calcium in mmol/L. Understanding the difference between total, corrected, and ionised calcium is important for accurate interpretation.
Total calcium (adults)
The standard measurement. About 40% is bound to albumin, so low albumin can make total calcium look falsely low.
Corrected calcium
Adjusted for albumin level. Formula: corrected Ca = total Ca + 0.02 × (40 – albumin g/L). This is the value your GP will use if your albumin is abnormal.
Ionised calcium
The biologically active fraction. Most accurate measurement but requires special handling. Used when total calcium is borderline.
Mild hypercalcaemia
May be asymptomatic or cause subtle symptoms (fatigue, constipation, mild confusion). Often discovered incidentally.
Moderate hypercalcaemia
Symptoms usually present. Dehydration, nausea, abdominal pain, polyuria. Investigation and treatment needed promptly.
Severe hypercalcaemia
Medical emergency. Risk of cardiac arrhythmias, renal failure, coma. Requires immediate IV fluids and hospital admission.
Symptoms — "Bones, Stones, Groans, and Moans"
Medical students learn the classic mnemonic for hypercalcaemia symptoms. Many patients with mild elevation have no symptoms at all.
Bones
Bone pain, osteoporosis, pathological fractures. Excess PTH pulls calcium from bones, weakening them over years. DEXA scans may show reduced bone density.
Stones
Kidney stones (calcium oxalate or phosphate), nephrocalcinosis. High urinary calcium precipitates in the kidneys. Flank pain, haematuria, recurrent UTIs.
Groans
Constipation, nausea, vomiting, abdominal pain, peptic ulcers, pancreatitis (rare). Calcium slows gut motility and increases gastric acid secretion.
Moans
Fatigue, depression, confusion, poor concentration, memory problems, drowsiness. In severe cases: lethargy, psychosis, or coma.
Common Causes of High Calcium
About 90% of hypercalcaemia is caused by either primary hyperparathyroidism or malignancy.
Primary hyperparathyroidism
The most common cause in outpatients, accounting for roughly 50–60% of cases. One or more parathyroid glands become overactive (usually a benign adenoma) and produce excess PTH. Most common in postmenopausal women. Often mild and discovered incidentally.
Malignancy
The most common cause in hospitalised patients. Cancers of the lung, breast, kidney, and multiple myeloma can raise calcium through bone destruction or by secreting PTH-related protein (PTHrP). Usually moderate to severe.
Vitamin D excess
Over-supplementation with vitamin D can cause hypercalcaemia by increasing intestinal calcium absorption. Granulomatous diseases (sarcoidosis, tuberculosis) can also produce excess active vitamin D.
Thiazide diuretics
Hydrochlorothiazide and indapamide reduce urinary calcium excretion, potentially raising blood levels. The effect is usually mild and reversible when the drug is stopped.
Immobilisation
Prolonged bed rest causes bone breakdown and calcium release. Particularly relevant for elderly patients after hip fracture, stroke, or spinal cord injury.
Familial hypocalciuric hypercalcaemia
A benign genetic condition causing lifelong mild hypercalcaemia (typically 2.60–2.80) with low urinary calcium. Important to distinguish from hyperparathyroidism because it does NOT need treatment.
Lithium
Used for bipolar disorder, lithium resets the parathyroid calcium set-point upward, causing mild hypercalcaemia in 10–20% of long-term users.
Thyrotoxicosis
Severe hyperthyroidism increases bone turnover and can cause mild hypercalcaemia. Usually resolves when the thyroid disorder is treated.
What Your GP Will Do Next
The investigation follows a logical pathway. PTH is the key that unlocks the diagnosis.
1. Confirm with corrected calcium
Your GP will check your albumin level and calculate corrected calcium. If albumin is low, total calcium may underestimate the true level.
2. Check PTH level
This is the single most important next test. High PTH + high calcium = primary hyperparathyroidism. Low/suppressed PTH + high calcium = non-PTH cause (malignancy, vitamin D excess, etc.).
3. Measure vitamin D
Both 25-hydroxyvitamin D (storage form) and sometimes 1,25-dihydroxyvitamin D (active form) will be checked to identify excess supplementation or granulomatous disease.
4. Check kidney function
Creatinine, eGFR, and urine calcium will be assessed. Hypercalcaemia can damage the kidneys. A 24-hour urine calcium helps distinguish hyperparathyroidism from FHH.
5. Additional investigations
Depending on PTH results: if high PTH, a sestamibi scan or neck ultrasound localises the overactive gland. If low PTH, investigations for malignancy (CT, myeloma screen with protein electrophoresis).
6. Specialist referral
Endocrinologist if hyperparathyroidism is confirmed. Oncologist if malignancy is suspected. In Australia, most endocrinology outpatient clinics are Medicare-covered.
Frequently Asked Questions
Should I stop taking vitamin D if my calcium is high?
If your calcium is elevated and you are taking vitamin D supplements, your GP will likely pause them until the cause is identified. However, do not stop prescribed medications without consulting your GP first — the high calcium may have a different cause entirely.
Does high calcium always mean cancer?
No. While malignancy is an important cause, primary hyperparathyroidism is actually more common overall. In outpatient settings where calcium is found incidentally on routine blood work, hyperparathyroidism is the most likely diagnosis.
What is the difference between total and ionised calcium?
Total calcium measures all calcium in your blood — the portion bound to albumin (about 40%), bound to other molecules (about 10%), and the free/ionised fraction (about 50%). Ionised calcium is the biologically active form.
I have primary hyperparathyroidism. Do I need surgery?
Not always. Mild, asymptomatic hyperparathyroidism can be monitored. Surgery is recommended if calcium is more than 0.25 mmol/L above the upper limit, age under 50, osteoporosis on DEXA, eGFR below 60, or kidney stones. Surgery is curative in over 95% of cases.
Can dehydration cause high calcium?
Dehydration concentrates the blood and can mildly elevate total calcium. However, dehydration alone rarely pushes calcium above 2.70 mmol/L. Your GP will recheck after rehydration.
How often should calcium be monitored if mildly elevated?
If monitoring mild hyperparathyroidism conservatively, typical follow-up includes calcium and PTH every 6–12 months, annual creatinine/eGFR, and a DEXA scan every 1–2 years. SmarterBlood can track your trend over time.
Related Reading
Track Your Calcium Over Time
Upload your blood test results and SmarterBlood will chart your calcium, PTH, and vitamin D trends automatically — so you and your GP can monitor the pattern.
This information is based on guidelines from the Royal College of Pathologists of Australasia (RCPA), Endocrine Society of Australia, and Kidney Health Australia. Reference ranges may vary between pathology providers. SmarterBlood provides educational information only and is not a substitute for professional medical advice.