← All Tests
Lab Test

Calcium Blood Test: Hypercalcaemia, Hypocalcaemia & What They Mean

Calcium is one of the most tightly regulated minerals in the body. Abnormal levels can indicate parathyroid disease, cancer, vitamin D disorders, or kidney problems.

Written and clinically reviewed by Suman Konda, PharmD, Clinical Pharmacist · Based on peer-reviewed sources · Editorial policy · Not medical advice

Last reviewed and updated: · How we check our content

Normal corrected calcium
2.20–2.60 mmol/L
Adjusted for albumin
Correct for every 4 g/L albumin below 40
Hypercalcaemia >2.6
Always investigate
Most common cause
Primary hyperparathyroidism

Adjusting Calcium for Albumin

Corrected Calcium Formula

Corrected calcium = Measured calcium + 0.02 × (40 − albumin). Low albumin lowers total calcium without affecting ionised (biologically active) calcium: adjusted calcium corrects for this. Ionised calcium measurement avoids this confusion.

Causes of Hypercalcaemia (High Calcium)

Cause% of CasesClue
Primary hyperparathyroidism50%High PTH with high Ca²⁺
Malignancy25–30%Low PTH; weight loss, anaemia
Vitamin D toxicity<5%History of high-dose supplementation
SarcoidosisUncommonLung involvement, raised ACE
Thiazide diureticsDrug causeRecent drug history
Milk-alkali syndromeUncommonExcessive calcium supplement use

Symptoms of Hypercalcaemia

  • Remembered as 'Bones, Stones, Groans, Moans, Psychic Overtones'
  • Bones: bone pain, fractures
  • Stones: renal calculi (kidney stones)
  • Groans: constipation, nausea, vomiting
  • Moans: muscle weakness, fatigue
  • Psychic: confusion, depression, lethargy
PTH Is Always the Next TestAlways check PTH alongside calcium. High PTH with high calcium = primary hyperparathyroidism. Low/suppressed PTH with high calcium = malignancy or vitamin D excess until proven otherwise.
What is hypercalcaemia of malignancy?
Cancer can raise calcium via PTHrP (parathyroid-hormone-related protein), bone metastases, or ectopic vitamin D production. It's a sign of advanced disease and requires urgent management.
What causes low calcium (hypocalcaemia)?
Vitamin D deficiency, hypoparathyroidism (post-thyroid surgery), magnesium deficiency (blocks PTH), acute pancreatitis, renal failure, and malabsorption syndromes.
What are symptoms of low calcium?
Tingling in fingers/lips, muscle cramps (tetany), Trousseau's sign (carpal spasm with BP cuff), Chvostek's sign (facial twitch with tap), and in severe cases, seizures and laryngospasm.
How is hypercalcaemia treated?
IV fluids (rehydration) is the first step. Bisphosphonates (zoledronic acid) for malignancy-related hypercalcaemia. Treat the underlying cause. Steroids work for sarcoidosis and vitamin D toxicity.
Vitamin DCalcium regulation

Frequently asked questions

Can a Calcium result be misleading?
It can. Sample handling shifts Calcium measurably: a prolonged tourniquet, a delay before processing, the wrong tube or a recent supplement all affect the value in mmol/L. An unexpected result in someone who feels well is often worth repeating before anything else.
What is worth asking a doctor about an abnormal Calcium?
Whether it needs repeating, whether a medicine or recent illness explains it, how far outside the range it actually falls, and whether it changes management or simply needs watching. Those four questions cover most of what matters.
Does age or sex affect the Calcium reference range?
For several analytes it does, which is why some reports print separate intervals. Where your laboratory gives an age or sex-specific range for Calcium, that range takes precedence over any general figure.

References

The clinical information on this page is drawn from peer-reviewed sources indexed by the US National Library of Medicine. Links go to the source so you can read it yourself.

  1. Primary Hyperparathyroidism. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf NBK441895
  2. Electrolytes. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf NBK541123

Related reading

Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.

Getting the sample right

Calcium is one of the tests most affected by collection technique. A prolonged tourniquet causes local haemoconcentration and falsely raises the measured value, so the cuff should be released promptly. Clenching the fist repeatedly has the same effect. Because almost half of circulating calcium is bound to albumin, the total calcium moves with the albumin level, which is why laboratories report an adjusted or corrected calcium. In situations where that adjustment is unreliable, such as marked protein abnormalities, critical illness or myeloma, an ionised calcium measured directly is the more trustworthy figure.

The two causes that account for most cases

In practice the large majority of hypercalcaemia, commonly quoted as around 90%, is explained by two diagnoses. Primary hyperparathyroidism dominates in outpatients and is typically mild, long-standing and found incidentally, with a parathyroid hormone level that is inappropriately normal or raised for the calcium. Malignancy dominates in hospital inpatients, tends to produce higher calcium levels that rise more quickly, and suppresses parathyroid hormone. Measuring PTH alongside calcium therefore separates the two efficiently and is the standard next step rather than an additional extra.

Other causes worth knowing

  • Thiazide diuretics and lithium, both of which raise calcium and may unmask underlying hyperparathyroidism.
  • Excess vitamin D or calcium supplementation, increasingly common with high-dose over-the-counter products.
  • Granulomatous disease such as sarcoidosis and tuberculosis, through unregulated vitamin D activation.
  • Prolonged immobilisation, particularly after major injury in younger people with high bone turnover.
  • Familial hypocalciuric hypercalcaemia, a benign inherited condition that mimics hyperparathyroidism and is important to identify because surgery does not help it.

Low calcium

Hypocalcaemia most often follows thyroid or parathyroid surgery, severe vitamin D deficiency, chronic kidney disease, or magnesium depletion, which impairs parathyroid hormone release and action. Symptoms progress from tingling around the mouth and fingertips to muscle cramps and, when severe, tetany, seizures and cardiac effects with a prolonged QT interval. As with potassium, the speed of the fall matters: a gradual decline is often surprisingly well tolerated, while an abrupt drop after surgery can be symptomatic at a higher level.