Lab result explainedMetabolic panelLast updated November 8, 2026

Calcium blood test: what high and low calcium (hypercalcemia and hypocalcemia) mean

Calcium (serum and corrected calcium) (Ca) · Basic or comprehensive metabolic panel (BMP/CMP); ionized calcium on blood gas or separate test · reported in mg/dL (mmol/L outside the US; 1 mmol/L = 4.0 mg/dL)

A calcium blood test measures the calcium circulating in your blood, which is less than 1 percent of the calcium in your body; the other 99 percent is in bone. Blood calcium is kept within a very narrow band, normally about 8.5 to 10.5 mg/dL for total calcium, by parathyroid hormone (PTH) and vitamin D, because nerves, muscles, the heart and clotting all depend on it. A result outside that band is therefore usually a signal that one of those control systems has a problem, rather than a reflection of how much calcium you eat.

About 40 percent of blood calcium is bound to albumin, so the total calcium reading moves with albumin even when the active, free (ionized) calcium is normal. Clinicians adjust for this with the corrected calcium formula: corrected calcium = measured calcium + 0.8 × (4.0 − albumin in g/dL). A calcium of 8.0 mg/dL with an albumin of 2.5 corrects to 9.2 and is normal. Where accuracy matters, ionized calcium (normal about 4.6 to 5.3 mg/dL, or 1.15 to 1.33 mmol/L) is measured directly.

High calcium (hypercalcemia) is most often caused by an overactive parathyroid gland in people who feel well, and by cancer in people who are ill; vitamin D excess, certain medications and granulomatous diseases make up most of the rest. Low calcium (hypocalcemia) usually comes from vitamin D deficiency, kidney disease, low magnesium or damaged parathyroid glands after neck surgery. The single most useful companion test is PTH, which tells you whether the parathyroid glands are causing the abnormality or responding appropriately to it.

Ca at a glance

  • What it is: total calcium in blood (40 percent bound to albumin, 50 percent free or ionized, 10 percent complexed); tightly controlled by parathyroid hormone and vitamin D.
  • Normal: total calcium 8.5–10.5 mg/dL (2.12–2.62 mmol/L; many labs 8.6–10.3); ionized calcium 4.6–5.3 mg/dL (1.15–1.33 mmol/L). Labs differ.
  • Corrected calcium = measured calcium + 0.8 × (4.0 − albumin g/dL). Use it whenever albumin is below 4.0; a low total calcium with a low albumin is often normal once corrected.
  • High (hypercalcemia): above 10.5 mg/dL. Mild 10.5–11.9, moderate 12–13.9, severe 14 or above (a medical emergency). Causes: primary hyperparathyroidism, cancer, vitamin D excess, thiazides, lithium, sarcoidosis, excess calcium plus antacids.
  • Low (hypocalcemia): below 8.5 mg/dL after correction, or ionized below 4.6 mg/dL. Causes: vitamin D deficiency, kidney disease, low magnesium, hypoparathyroidism after thyroid or neck surgery, pancreatitis. Below 7.0 mg/dL with tingling, cramps or seizures is an emergency.
  • Next step: repeat with albumin (or ionized calcium) and PTH; high calcium with a high or mid-normal PTH is hyperparathyroidism, with a suppressed PTH points to cancer or vitamin D excess.

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What Ca measures

Calcium in blood exists in three forms: about 50 percent is free, ionized calcium, which is the biologically active form that nerves and muscles respond to; about 40 percent is bound to proteins, mostly albumin; and about 10 percent is complexed with small anions such as phosphate, citrate and bicarbonate. The standard test measures total calcium, all three forms together, by a colorimetric method on the same sample as the metabolic panel. Ionized calcium is measured separately with an ion-selective electrode, often on a blood gas analyzer, and must be collected and handled carefully because changes in blood pH shift calcium on and off albumin.

Because of the albumin binding, total calcium rises and falls with albumin. Each 1 g/dL change in albumin shifts total calcium by about 0.8 mg/dL, which is the basis of the corrected calcium formula. The correction is a reasonable estimate in most outpatients but is less reliable in critically ill people, in advanced kidney disease and when blood pH is abnormal, which is why ionized calcium is preferred in intensive care, during surgery and in dialysis units. Alkalosis (for example from hyperventilation) increases albumin binding and lowers ionized calcium without changing total calcium, which is why anxious over-breathing causes tingling fingers and lips.

Blood calcium is controlled minute to minute by parathyroid hormone from four small glands behind the thyroid. When calcium falls, PTH rises and pulls calcium from bone, tells the kidneys to reabsorb more calcium and excrete phosphate, and activates vitamin D (calcitriol), which increases calcium absorption from food. When calcium rises, PTH switches off. This feedback loop is why the PTH level is always interpreted together with calcium: a high calcium should suppress PTH to below about 20 pg/mL, so a PTH that is high or even mid-normal in the face of a high calcium means the parathyroid glands are the problem. Calcium is best drawn fasting, without a prolonged tourniquet, since both a recent meal with calcium supplements and venous stasis raise it slightly.

Normal range for Ca

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

GroupTypical range (mg/dL (mmol/L outside the US; 1 mmol/L = 4.0 mg/dL))Notes
Total calcium, adults8.5–10.5 mg/dL (2.12–2.62 mmol/L)Many labs use 8.6–10.3 or 8.8–10.2 mg/dL. Labs differ; use the printed range. Slightly lower (by about 0.1–0.2) in older adults.
Ionized calcium, adults4.6–5.3 mg/dL (1.15–1.33 mmol/L)The active fraction; not affected by albumin. Preferred in critical illness, kidney disease and when albumin is very abnormal.
Children8.8–10.8 mg/dLHigher in infants and during growth; newborns can run 7.6–10.4 in the first days.
Corrected calciumMeasured calcium + 0.8 × (4.0 − albumin in g/dL)Apply when albumin is below 4.0 g/dL. Example: calcium 8.2 with albumin 2.8 = 8.2 + 0.96 = 9.2 mg/dL, normal. Less accurate in intensive care and advanced kidney disease.
Mild hypercalcemia10.5–11.9 mg/dLUsually primary hyperparathyroidism in people who feel well; often found incidentally. Repeat with albumin and PTH.
Moderate hypercalcemia12.0–13.9 mg/dLSymptoms common (thirst, constipation, fatigue, confusion). Cancer and hyperparathyroidism are the main causes; needs prompt evaluation.
Severe hypercalcemia (hypercalcemic crisis)14.0 mg/dL or aboveDehydration, confusion, kidney injury and heart rhythm disturbance; a medical emergency usually treated in hospital with intravenous fluids and bone-protecting drugs.
Mild hypocalcemia7.5–8.4 mg/dL (corrected) or ionized 4.0–4.5 mg/dLOften from vitamin D deficiency, kidney disease or low magnesium; may cause tingling or cramps.
Severe hypocalcemiaBelow 7.0 mg/dL (corrected) or ionized below 3.2 mg/dL (0.8 mmol/L)Risk of muscle spasm (tetany), laryngospasm, seizures and a prolonged QT interval on ECG; a medical emergency.

High calcium (hypercalcemia)

A high calcium means more calcium is entering the blood from bone, gut or kidney than the body's control system is removing. Two conditions account for about 90 percent of cases. In people who feel well and whose high calcium was found on a routine panel, the cause is usually primary hyperparathyroidism: one (occasionally more) of the four parathyroid glands has developed a benign growth and produces PTH regardless of the calcium level. It affects about 1 in 100 people over 50, is three times more common in women, and typically produces a calcium of 10.5 to 11.5 mg/dL that drifts up slowly over years, with a PTH that is high or inappropriately mid-normal. In people who are unwell, the cause is usually cancer: lung, breast, kidney, head and neck cancers and multiple myeloma raise calcium either by releasing a PTH-like protein (PTHrP) or by dissolving bone directly, and the PTH is suppressed.

The remaining causes are sorted out by the PTH, phosphate and vitamin D levels. Excess vitamin D from high-dose supplements (typically more than 10,000 IU a day for months, giving a 25-hydroxyvitamin D above 150 ng/mL) raises calcium with a low PTH and a high phosphate. Granulomatous diseases such as sarcoidosis and tuberculosis make their own active vitamin D in immune cells. Thiazide diuretics reduce calcium loss in urine and can unmask mild hyperparathyroidism; lithium raises the set point of the parathyroid glands. Taking several grams of calcium carbonate a day as antacids or supplements can cause the calcium-alkali syndrome, now the third most common cause of hypercalcemia in hospital. Prolonged immobilisation, an overactive thyroid, adrenal insufficiency and a rare inherited condition called familial hypocalciuric hypercalcemia (FHH, picked up by a very low urine calcium) complete the list.

Symptoms depend on how high and how fast. A calcium of 10.5 to 11.5 that has crept up over years often causes nothing, or only vague tiredness, aches and constipation, though it quietly increases kidney stones and bone loss. Between 12 and 14 mg/dL, thirst, frequent urination, nausea, constipation, muscle weakness, poor concentration and low mood are usual. Above 14 mg/dL, or with a rapid rise, confusion, dehydration, kidney injury and heart rhythm disturbance (a short QT interval) can follow, and the person needs hospital treatment the same day.

Common causes

  1. Primary hyperparathyroidism

    A benign adenoma of one parathyroid gland in about 85 percent of cases, or enlargement of all four, produces PTH independently of calcium. Calcium is usually 10.5–11.5 mg/dL with a PTH above 65 pg/mL or inappropriately normal (above about 20–25 pg/mL), a low-normal phosphate and a high urine calcium. The commonest cause in outpatients.

  2. Cancer

    Squamous cancers of the lung, head and neck, kidney, bladder and ovary release PTH-related protein (PTHrP); breast cancer, myeloma and lymphoma dissolve bone directly; some lymphomas make active vitamin D. Calcium is often above 12 mg/dL, PTH is suppressed below 20 pg/mL, and the cancer is usually already known. The commonest cause in hospital.

  3. Vitamin D excess

    Supplements above 10,000 IU a day for months, dosing errors with high-strength products, or over-fortified foods raise 25-hydroxyvitamin D above 150 ng/mL (375 nmol/L), increasing gut calcium absorption; PTH is low and phosphate high. Recovery takes weeks because vitamin D is stored in fat.

  4. Calcium-alkali (milk-alkali) syndrome

    More than about 4 g of calcium a day from calcium carbonate antacids or supplements, especially with vitamin D or in kidney impairment, causes high calcium, metabolic alkalosis and kidney injury; now accounts for around 10 percent of hospital hypercalcemia.

  5. Thiazide diuretics and lithium

    Hydrochlorothiazide and chlorthalidone reduce urinary calcium loss and raise calcium by 0.2–0.5 mg/dL, often unmasking mild hyperparathyroidism; lithium raises the threshold at which the parathyroids switch off, causing a PTH-dependent hypercalcemia in 10–15 percent of long-term users.

  6. Granulomatous diseases

    Sarcoidosis, tuberculosis, fungal infections and some lymphomas contain activated macrophages that convert vitamin D to its active form unchecked; calcium rises especially after sun exposure or vitamin D supplements, with a low PTH and a high 1,25-dihydroxyvitamin D.

  7. Immobilisation

    Prolonged bed rest, spinal cord injury or a plaster cast in people with high bone turnover (adolescents, Paget's disease, hyperthyroidism) releases calcium from bone faster than the kidneys can clear it.

  8. Hyperthyroidism and adrenal insufficiency

    Thyroid hormone excess speeds bone turnover and mildly raises calcium in up to 20 percent of people with an overactive thyroid; Addison's disease causes hypercalcemia through dehydration and reduced kidney calcium excretion.

  9. Familial hypocalciuric hypercalcemia (FHH)

    An inherited change in the calcium-sensing receptor gives lifelong mild hypercalcemia (usually 10.5–11.5 mg/dL) with a normal or mildly raised PTH and a very low urine calcium; it is benign and must not be mistaken for hyperparathyroidism, since surgery does not help.

  10. Dehydration and sample artefact

    Hemoconcentration and a prolonged tourniquet raise total calcium by 0.2–0.5 mg/dL; a high albumin does the same. A repeat fasting sample with a short tourniquet time and an albumin or ionized calcium resolves it.

Symptoms that can go with it

  • Often none when calcium is 10.5–11.5 mg/dL and has risen slowly
  • Excessive thirst and passing large amounts of urine, including at night
  • Constipation, nausea, loss of appetite and abdominal pain
  • Fatigue, muscle weakness and aching bones or joints
  • Low mood, poor concentration, irritability or, at higher levels, confusion and drowsiness
  • Kidney stones, or flank pain and blood in the urine
  • Bone thinning (osteoporosis) and fractures over years of untreated hyperparathyroidism
  • Palpitations or an abnormal heart rhythm at very high levels

Low calcium (hypocalcemia)

The first question with a low total calcium is whether it is really low. Because 40 percent of calcium is bound to albumin, a low albumin from illness, liver disease or kidney protein loss pulls total calcium down without changing the free, active calcium. Correcting for albumin (adding 0.8 mg/dL for every 1 g/dL that albumin is below 4.0), or measuring ionized calcium directly, settles this, and a large proportion of low calcium results on routine panels turn out to be normal once corrected. Mild true hypocalcemia (corrected calcium 7.5 to 8.4 mg/dL) is common in hospital and often has no symptoms.

When calcium is genuinely low, the PTH level again divides the causes. If PTH is high, the parathyroid glands are responding appropriately and the problem lies elsewhere: vitamin D deficiency (the commonest cause in the community, especially with little sun exposure, darker skin, malabsorption or obesity), chronic kidney disease (the kidneys cannot activate vitamin D and retain phosphate, which binds calcium), acute pancreatitis (calcium is deposited in damaged fat), tumour lysis or rhabdomyolysis (phosphate release), and medications such as bisphosphonates, denosumab and some anti-seizure drugs. If PTH is low or inappropriately normal, the glands themselves are failing: hypoparathyroidism after thyroid or parathyroid surgery (temporary in 20 to 30 percent of thyroidectomies, permanent in 1 to 3 percent), autoimmune destruction, radiation, or infiltration by iron or copper. Low magnesium (below about 1.2 mg/dL) is a special case, because it both blocks PTH release and makes bone resistant to it, so calcium will not correct until magnesium is replaced.

Symptoms come from nerves and muscles becoming over-excitable. Early signs are tingling or numbness around the mouth and in the fingers and toes, muscle cramps and twitching; tapping the facial nerve in front of the ear can trigger a facial twitch (Chvostek sign) and inflating a blood pressure cuff can cause the hand to spasm (Trousseau sign). As calcium falls below about 7.0 mg/dL, or quickly, painful sustained spasms (tetany), spasm of the voice box with difficulty breathing, seizures, a prolonged QT interval and heart failure can occur, which is why severe or symptomatic hypocalcemia is treated urgently in hospital.

Common causes

  1. Low albumin (pseudohypocalcemia)

    The commonest reason for a low total calcium on a routine panel; the free calcium is normal. Corrected calcium or ionized calcium confirms it. No treatment for calcium is needed.

  2. Vitamin D deficiency

    A 25-hydroxyvitamin D below 12–20 ng/mL reduces calcium absorption from food; PTH rises to compensate, so calcium is often only mildly low until deficiency is severe. Common with limited sun exposure, darker skin, malabsorption (celiac disease, bariatric surgery) and obesity.

  3. Chronic kidney disease

    Failing kidneys cannot convert vitamin D to its active form and retain phosphate, which binds calcium; PTH rises (secondary hyperparathyroidism). Calcium falls as eGFR drops below about 30 mL/min.

  4. Low magnesium

    Magnesium below about 1.2 mg/dL blocks PTH release and action. Causes include proton pump inhibitors, diuretics, alcohol dependence, diarrhoea and some chemotherapy. Calcium stays low until magnesium is corrected.

  5. Hypoparathyroidism after thyroid or neck surgery

    Removal of, or damage to the blood supply of, the parathyroid glands during thyroidectomy or parathyroidectomy; calcium falls within 24–72 hours, is temporary in 20–30 percent and permanent in 1–3 percent. PTH is low.

  6. Autoimmune and genetic hypoparathyroidism

    Autoimmune destruction (sometimes with Addison's disease and candidiasis), DiGeorge syndrome, activating mutations of the calcium-sensing receptor and pseudohypoparathyroidism (resistance to PTH) all cause lifelong low calcium with low or ineffective PTH.

  7. Medications

    Bisphosphonates and denosumab (especially with vitamin D deficiency or kidney disease), cinacalcet, loop diuretics, phenytoin and phenobarbital, foscarnet, cisplatin, and large transfusions (citrate binds calcium) lower calcium.

  8. Acute pancreatitis

    Calcium binds to fatty acids released by damaged pancreatic tissue; a calcium below 8.0 mg/dL within 48 hours is a marker of severe pancreatitis.

  9. High phosphate: tumour lysis, rhabdomyolysis, phosphate enemas

    Sudden release or absorption of phosphate binds calcium and deposits it in tissues; calcium can fall rapidly and dangerously, with high potassium and kidney injury.

  10. Critical illness, sepsis and alkalosis

    Ionized calcium is low in up to half of intensive care patients through several mechanisms; hyperventilation and alkalosis increase albumin binding and lower ionized calcium acutely, causing tingling and cramps.

Symptoms that can go with it

  • Tingling or numbness around the mouth and in the fingers and toes
  • Muscle cramps, twitching or aching, particularly in the hands, feet and face
  • Carpopedal spasm: the fingers draw together and the wrist flexes, sometimes triggered by a blood pressure cuff
  • Fatigue, anxiety, irritability, low mood or brain fog
  • Dry skin, brittle nails, coarse hair and dental enamel defects with long-standing low calcium
  • Cataracts and, over years, calcium deposits in the brain with chronic hypoparathyroidism
  • Hoarseness, wheeze or difficulty breathing from spasm of the voice box in severe cases
  • Seizures, palpitations or fainting from a prolonged QT interval when calcium is very low

Read it alongside

  • Parathyroid hormone (PTH) — the key companion test; high calcium with a high or mid-normal PTH means primary hyperparathyroidism, high calcium with a suppressed PTH (under 20 pg/mL) points to cancer, vitamin D excess or granulomatous disease; low calcium with a high PTH means the glands are responding to vitamin D deficiency or kidney disease, and with a low PTH means hypoparathyroidism.
  • Albumin — needed for corrected calcium; each 1 g/dL below 4.0 adds 0.8 mg/dL to the measured calcium.
  • Ionized calcium — the direct measurement of active calcium, used when albumin or pH is abnormal, in kidney disease and in intensive care.
  • Phosphorus — low in primary hyperparathyroidism and PTHrP-driven cancer; high in kidney disease, hypoparathyroidism, vitamin D excess and tumour lysis.
  • 25-hydroxyvitamin D — identifies deficiency as the cause of low calcium, or excess as the cause of high calcium; 1,25-dihydroxyvitamin D is raised in granulomatous disease and some lymphomas.
  • Magnesium — low magnesium blocks PTH and must be corrected before calcium will respond.
  • Creatinine and eGFR — kidney disease causes low calcium and high phosphate; hypercalcemia itself injures the kidneys and causes stones.
  • Alkaline phosphatase — raised when bone turnover is high (hyperparathyroidism with bone disease, bone metastases, Paget's disease, healing fractures) and in vitamin D deficiency with osteomalacia.

What usually happens next

  1. A single mildly abnormal calcium is repeated fasting, with albumin (or ionized calcium) and a PTH drawn at the same time; the corrected value and the PTH pattern decide everything that follows.
  2. If calcium is high with a high or non-suppressed PTH, expect a 24-hour urine calcium (to exclude FHH), a bone density scan, kidney function and imaging of the parathyroid glands (ultrasound or sestamibi scan) if surgery is being considered; parathyroidectomy is recommended when calcium is more than 1 mg/dL above normal, bone density is low, kidney function is reduced, there are stones, or you are under 50.
  3. If calcium is high with a suppressed PTH, the work-up includes PTHrP, 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, serum protein electrophoresis and free light chains, a chest X-ray, and a review of supplements, antacids and medications; imaging for cancer follows if these point that way.
  4. If calcium is low with a high PTH, 25-hydroxyvitamin D, magnesium, phosphate and kidney function are checked and the cause treated; if PTH is low or inappropriately normal, magnesium is checked and hypoparathyroidism is assessed, with an endocrinology referral.
  5. Bring a list of all supplements (calcium, vitamin D, vitamin A), antacids and medications (thiazides, lithium, bisphosphonates, denosumab, proton pump inhibitors) to the appointment; several of these are common and reversible causes.
  6. Ask for an ECG if calcium is above 12 or below 7.5 mg/dL or you have palpitations, as both extremes change the heart's electrical interval.

Diet, lifestyle and natural levers with evidence

What can move Ca once the cause is known. Nothing here replaces finding the cause.

Correct vitamin D deficiency (for low calcium)

Strong evidence

Vitamin D deficiency is the most common reversible cause of low calcium in the community. In trials and treatment series, repleting a 25-hydroxyvitamin D below 20 ng/mL with 1,000–2,000 IU of vitamin D3 a day, or the equivalent weekly dose, raises calcium into the normal range and lowers PTH within 4 to 12 weeks, and reverses the bone softening (osteomalacia) that severe deficiency causes. The Endocrine Society considers 30 ng/mL or above sufficient for calcium handling; 20 ng/mL is adequate for most of the population.

Vitamin D raises calcium in people with sarcoidosis, lymphoma or primary hyperparathyroidism, who should take it only under supervision. The tolerable upper intake is 4,000 IU a day for adults; toxicity (calcium above normal with a 25-hydroxyvitamin D above 150 ng/mL) usually requires more than 10,000 IU a day for months.

Replace low magnesium (for low calcium)

Strong evidence

When magnesium is below about 1.2 mg/dL, PTH cannot be released or act properly and calcium stays low regardless of calcium or vitamin D intake. Case series and small trials consistently show PTH rising within hours and calcium normalising within one to three days of magnesium replacement, while calcium given alone fails. Dietary sources (nuts, seeds, legumes, whole grains, leafy greens) provide 300–400 mg a day; oral supplements of 200–400 mg a day are used for mild deficiency, and intravenous magnesium for severe or symptomatic cases.

Proton pump inhibitors, diuretics and alcohol are common causes and need review. In kidney disease, magnesium can accumulate; supplements need monitoring. Oral magnesium causes diarrhoea at higher doses.

Meet, but do not exceed, the calcium requirement from food

Strong evidence

The recommended intake is 1,000 mg a day for adults, rising to 1,200 mg for women over 50 and everyone over 70, with an upper limit of 2,000–2,500 mg. Because PTH and vitamin D regulate blood calcium, dietary intake within this range barely moves the serum level in healthy people; its effect is on bone, where adequate intake plus vitamin D reduces fractures by around 10–15 percent in older adults in meta-analyses. Food sources (dairy, fortified plant milks, tofu set with calcium, canned fish with bones, leafy greens) are preferred over supplements, which in some meta-analyses have been associated with a small increase in kidney stones and cardiovascular events.

In primary hyperparathyroidism, normal dietary calcium is recommended, but supplements can raise calcium further; people with high calcium should not take calcium supplements unless advised.

Limit calcium carbonate antacids and high-dose supplements (for high calcium)

Moderate evidence

The calcium-alkali syndrome now accounts for about 10 percent of hospital admissions for hypercalcemia, most often in women taking calcium carbonate for bone health or heartburn alongside vitamin D, and in people with reduced kidney function. Intakes above about 4 g of elemental calcium a day are typical, but it has occurred at 1.5–2 g a day with kidney impairment. Case series show calcium returning to normal within days of stopping the supplements and rehydrating. Keeping total supplemental calcium at or below 500–600 mg a day, and using a non-calcium antacid if needed, removes this risk.

Stay well hydrated (for mild high calcium)

Moderate evidence

High calcium impairs the kidneys' ability to concentrate urine, which causes dehydration, which in turn reduces calcium excretion, a cycle that pushes calcium higher. Intravenous saline is the first treatment for severe hypercalcemia precisely because it breaks this cycle, lowering calcium by 1–2 mg/dL in the first day. For people with mild primary hyperparathyroidism being monitored rather than operated on, guidelines recommend drinking enough to avoid dehydration (around 2–3 litres a day unless restricted for heart or kidney disease), which also lowers kidney stone risk.

People with heart failure or advanced kidney disease should follow their clinician's fluid targets.

Weight-bearing activity and avoiding prolonged immobilisation

Preliminary evidence

Bed rest and immobilisation release calcium from bone and can raise blood calcium, particularly in young people and those with high bone turnover; in spinal cord injury, hypercalcemia develops in 10–25 percent within the first months. Early mobilisation and standing or weight-bearing exercise reduce this bone loss in rehabilitation studies. In people with mild primary hyperparathyroidism, regular physical activity is recommended to maintain bone density, though it does not change the calcium level itself.

When to see a clinician promptly

  • A calcium of 14 mg/dL or above, or any high calcium with confusion, severe vomiting, severe dehydration, drowsiness or palpitations: hypercalcemic crisis, an emergency.
  • A calcium of 12–13.9 mg/dL, or any high calcium in someone with a known or suspected cancer, within a day or two.
  • A corrected calcium below 7.0 mg/dL, or any low calcium with muscle spasms, tingling that is spreading, difficulty breathing, seizures or fainting: severe hypocalcemia, an emergency.
  • Low calcium in the days after thyroid, parathyroid or other neck surgery with tingling or cramps.
  • Persistent mildly high calcium (10.5–11.9 mg/dL) on two tests, to have PTH measured and primary hyperparathyroidism assessed, especially with kidney stones, bone loss or fractures.
  • High calcium in anyone taking high-dose vitamin D, calcium supplements or antacids, lithium or a thiazide diuretic, to review these before anything else.

Frequently asked questions

What is a normal calcium level in blood?

For adults, total calcium of about 8.5 to 10.5 mg/dL (2.12 to 2.62 mmol/L); many labs use 8.6 to 10.3. Ionized calcium, the free active form, is normally 4.6 to 5.3 mg/dL (1.15 to 1.33 mmol/L). Children run slightly higher. If your albumin is below 4.0 g/dL, the total calcium should be corrected before comparing with the range.

Is a calcium of 10.4, 10.6 or 11 high?

A calcium of 10.4 is within or at the top of most ranges and is usually repeated rather than acted on. A calcium of 10.6 to 11 is mildly high; if it is confirmed on a repeat fasting test, the next step is a PTH level, since this band is typical of primary hyperparathyroidism in people who feel well. Dehydration, a long tourniquet and calcium supplements taken shortly before the draw can each add a few tenths, so a single value in this range is not a diagnosis.

How do you calculate corrected calcium?

Corrected calcium = measured total calcium + 0.8 × (4.0 − albumin in g/dL). For example, a calcium of 8.1 mg/dL with an albumin of 2.6 g/dL corrects to 8.1 + 0.8 × 1.4 = 9.2 mg/dL, which is normal. If your lab reports in mmol/L and g/L, the formula is calcium + 0.02 × (40 − albumin). The correction is an estimate; when accuracy matters, ionized calcium is measured directly.

What are the symptoms of high calcium?

Mild hypercalcemia often causes none. As calcium rises above about 11.5 to 12 mg/dL, people notice thirst, frequent urination, constipation, nausea, fatigue, muscle weakness, aching bones, poor concentration and low mood (summarised as stones, bones, abdominal groans and psychiatric moans). Above 14 mg/dL confusion, dehydration, kidney injury and heart rhythm problems can develop. Long-standing mild elevation causes kidney stones and bone thinning.

What causes high calcium levels?

In people who feel well, primary hyperparathyroidism (an overactive parathyroid gland) causes most cases. In people who are ill, cancer is the usual cause. Other causes include vitamin D excess, high-dose calcium carbonate antacids or supplements, thiazide diuretics, lithium, sarcoidosis and tuberculosis, an overactive thyroid, prolonged immobilisation and a benign inherited condition called familial hypocalciuric hypercalcemia. Dehydration raises it slightly. A PTH level separates the parathyroid cause from the rest.

What are the symptoms of low calcium?

Tingling or numbness around the lips, fingers and toes, muscle cramps and twitching are the earliest signs. As calcium falls further, the hands and feet can go into spasm, and severe hypocalcemia (below about 7 mg/dL) can cause seizures, spasm of the voice box with breathing difficulty and dangerous heart rhythms. Long-standing low calcium causes dry skin, brittle nails, dental problems and cataracts. Many people with mildly low calcium have no symptoms at all.

Does low calcium in blood mean I need more calcium in my diet?

Usually not. Blood calcium is controlled by parathyroid hormone and vitamin D, not by yesterday's intake, so a low result normally points to vitamin D deficiency, low magnesium, kidney disease, a parathyroid problem or simply a low albumin that makes total calcium look low. Correcting vitamin D or magnesium is what raises calcium in most cases. Adequate dietary calcium (about 1,000 to 1,200 mg a day) matters for bone health, and it is part of treating hypoparathyroidism, but on its own it will not fix a low blood level with another cause.

Does hyperparathyroidism need surgery?

Not always. Surgery to remove the overactive gland is recommended when calcium is more than 1 mg/dL above the upper limit of normal, when bone density is in the osteoporosis range or there has been a fracture, when kidney function is reduced (eGFR under 60) or there are kidney stones, or when the person is under 50; it is also reasonable for anyone who prefers it, since it is curative in about 95 percent of cases. People with mild disease who do not meet these criteria can be monitored with yearly calcium and kidney tests and bone density every one to two years, with attention to vitamin D, hydration and activity.

References

  1. Calcium blood test. MedlinePlus, US National Library of Medicine (2023)View source
  2. Calcium: fact sheet for health professionals. NIH Office of Dietary Supplements (2024)View source
  3. Hypercalcemia. Mayo Clinic (2024)View source
  4. Hypercalcemia. Merck Manual Professional Version (2023)
  5. Hypocalcemia. Merck Manual Professional Version (2023)
  6. Bilezikian JP, Khan AA, Silverberg SJ, et al.. Evaluation and management of primary hyperparathyroidism: summary statement and guidelines from the Fifth International Workshop. Journal of Bone and Mineral Research (2022)
  7. Minisola S, Pepe J, Piemonte S, Cipriani C. The diagnosis and management of hypercalcaemia. BMJ (2015)
  8. Cooper MS, Gittoes NJ. Diagnosis and management of hypocalcaemia. BMJ (2008)
  9. Stewart AF. Hypercalcemia associated with cancer. New England Journal of Medicine (2005)
  10. Patel AM, Goldfarb S. Got calcium? Welcome to the calcium-alkali syndrome. Journal of the American Society of Nephrology (2010)
  11. Payne RB, Little AJ, Williams RB, Milner JR. Interpretation of serum calcium in patients with abnormal serum proteins. British Medical Journal (1973)
  12. Carroll MF, Schade DS. A practical approach to hypercalcemia. American Family Physician (2003)

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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.