Calcium, Total
Total calcium is the amount of calcium in your blood. It supports your nerves, muscles, heart and bones, and it is on most routine panels.
AI-verified against cited sources. Awaiting expert reviewAlso called Ca, Ca totalLOINC 17861-6
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What it is
Calcium is a mineral your body needs for muscles, nerves, your heartbeat and blood clotting. About 99% of it is stored in your bones and teeth, and only a small amount circulates in your blood. This test measures total calcium. Part of it is attached to proteins, mostly albumin, and about half is free (ionized), which is the active form. Your body keeps the blood level in a narrow range with help from parathyroid hormone (PTH) and vitamin D.
Why it matters
Blood calcium that is too high or too low can affect your muscles, nerves, heart and kidneys. Because the body controls it so tightly, a result outside the range can be a clue about your parathyroid glands, vitamin D, kidneys or albumin level. Many mild changes are found by chance and have simple explanations, so a repeat test is common. This test does not show how much calcium is in your bones.
If it’s low
A result below your lab's range is called low calcium (hypocalcemia). A common reason is a low albumin level, which lowers the total number even when the free (ionized) calcium is in its usual range. True low calcium can come from low vitamin D, low magnesium, kidney problems or an underactive parathyroid gland. Mild low calcium often has no symptoms. Larger drops can cause tingling around the mouth or fingers and muscle cramps.
Common causes
- Low albumin (from illness, liver or kidney disease, or poor nutrition), which lowers the total number without changing the free calcium
- Low vitamin D, or trouble absorbing vitamin D and calcium
- Low magnesium
- Chronic kidney disease
- An underactive parathyroid gland, including after neck or thyroid surgery
- Inflammation of the pancreas (pancreatitis)
- Some medicines, including certain anti-seizure medicines and rifampin
- A blood tube contaminated with EDTA or citrate, which is a lab artifact
What can help
- Ask your clinician whether albumin, ionized calcium, magnesium, vitamin D and PTH should be checked
- Eat foods that provide calcium and vitamin D, such as dairy or fortified alternatives, canned fish with bones, leafy greens and eggs
- Talk with your clinician before starting any calcium or vitamin D supplement
If it’s high
A result above your lab's range is called high calcium (hypercalcemia). Mild high calcium often causes no symptoms and is often found on routine tests. Common explanations include dehydration, certain medicines and supplements, and an overactive parathyroid gland, which is the most common cause in people who aren't in the hospital. Less often it is linked to other conditions, including some cancers. Your clinician can put your result in context.
Common causes
- Dehydration, which can raise the number slightly
- A blood draw with the tourniquet on for a long time, which can give a falsely high result
- Calcium or vitamin D supplements, or calcium-based antacids, taken in large amounts
- Medicines such as thiazide water pills and lithium
- An overactive parathyroid gland (primary hyperparathyroidism)
- Too much vitamin D or vitamin A
- Long periods of not moving, such as bed rest
- Conditions such as sarcoidosis or an overactive thyroid
- Some cancers, especially those that affect bone (less common)
What can help
- Ask your clinician whether a repeat test, with albumin, PTH, vitamin D and kidney function, would help explain it
- Review every supplement, antacid and medicine you take with your clinician
- Drink fluids as your clinician advises, since dehydration can raise calcium
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
The usual range depends on sex and age. Choose women or men to see the one that applies.
- 18–598.7–10.2 mg/dL
Sources: Labcorp, Mayo Clinic Laboratories, Merck Manual Professional Edition
- Men, 60+8.6–10.2 mg/dL
Sources: Labcorp, Mayo Clinic Laboratories
- Women, 60+8.7–10.3 mg/dL
Sources: Labcorp, Mayo Clinic Laboratories
See Calcium by age and sex, with the U.S. survey numbers where they exist.
If this applies to you
Calcium means a little more for some people. Open the one that fits you.
Kidney disease or at risk
Calcium is one of the lab values KDIGO 2024 groups under CKD-mineral and bone disorder, along with phosphorus, PTH and vitamin D. These shifts begin early in CKD, so calcium is followed over time with phosphorus and PTH.
Taking lithium
Long-term lithium is linked to overactive parathyroid glands and high calcium. NICE suggests checking calcium every 6 months, and the FDA label asks for regular checks.
How common is your level?
NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.
Use the left and right arrow keys to read each age. Shift moves five years.
Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2015-2016, 2017-March 2020 (pre-pandemic), August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.
Explore Calcium by age and sex: every percentile as a table, with a download.
What can affect your result
- Albumin: total calcium rises or falls by about 0.8 mg/dL (0.2 mmol/L) for every 1 g/dL change in albumin
- Age: children and teenagers have different ranges, and some labs list a separate range for people 60 and older
- Hydration: dehydration can raise it slightly
- Medicines and supplements, including thiazide water pills, lithium, calcium and vitamin D
- Time of day: calcium varies a little across the day, so some labs prefer a fasting morning sample
- Blood draw: a long-lasting tourniquet can raise the result slightly, and tubes with EDTA or citrate can lower it
- Gadolinium MRI contrast can make some calcium tests read falsely low
- Tubes containing EDTA, citrate or oxalate interfere and can make calcium read falsely low (Labcorp).
- A tourniquet left on for a long time can raise the result artificially (Merck Manual).
- Very high protein levels can make total calcium read higher without changing the free (ionized) calcium (Merck Manual).
- Gadolinium MRI contrast can make some calcium tests read falsely low (Merck Manual).
- Thiazide water pills, lithium, and calcium or vitamin D supplements can raise calcium. Some anti-seizure medicines and other drugs can lower it.
Morning. Calcium varies a little across the day, and Labcorp prefers a fasting morning sample. Temporary causes such as dehydration can clear within days. Blood calcium is tightly controlled, so this test does not show changes in the calcium stored in your bones.
When to talk to a clinician
Contact the clinician who ordered the test soon if your calcium is outside your lab's range, especially with strong thirst, frequent urination, constipation, nausea, kidney stones, muscle cramps or tingling around the mouth. Large reference labs such as Quest and ARUP treat a result above 13 mg/dL (about 3.2 mmol/L) or below 6 mg/dL (about 1.5 mmol/L) as urgent. Call 911 or your local emergency number for chest pain, fainting, a seizure, severe confusion or an irregular heartbeat.
Questions you could ask
- How often should my calcium be rechecked?
- Do any of my medicines or health conditions affect my calcium?
- Could any of my supplements, antacids or medicines be raising my calcium?
- Should we repeat the test and check albumin, PTH, vitamin D and kidney function?
- Do I need an ionized calcium test?
- Could a low albumin explain this result?
Questions people ask
Is a slightly high or low calcium result something to worry about?
Small differences are common and often have simple causes, such as dehydration or a low albumin level. Clinicians often repeat the test before drawing conclusions. What matters most is how far outside the range it is, whether it stays there and whether you have symptoms.
Why does my clinician also look at my albumin?
Part of the calcium in your blood is attached to albumin. If albumin is low, total calcium reads low even when the active, free calcium is in its usual range. Clinicians may adjust the number for albumin or measure ionized calcium directly.
What is the difference between total calcium and ionized calcium?
Total calcium counts all the calcium in your blood. Ionized calcium counts only the free part, which is the active form. Total calcium is the routine test. Ionized calcium is usually ordered when the total result is unexpected or when protein levels are unusual.
Does this test show whether my bones are getting enough calcium?
No. Only about 1% of your body's calcium is in your blood, and your body keeps that level steady. A blood calcium result doesn't show how strong your bones are. A bone density scan (DEXA) is used for that.
How do I convert calcium between mg/dL and mmol/L?
Divide mg/dL by 4.008 to get mmol/L. Multiply mmol/L by 4.008 to get mg/dL. For example, 9.6 mg/dL is about 2.4 mmol/L.
Show the science and sources
Units
- 1 mg/dL = 1 mg/dL
- 1 mg/dL = 0.2495 mmol/L
- 1 mg/dL = 10 mg/L
- 1 mg/dL = 0.499 mEq/L
Open the Calcium unit converter
Is a change real?
Calcium naturally varies about 1.81% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 6% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: The European Biological Variation Study (EuBIVAS): a summary report.
For clinicians and researchers
About 40% of blood calcium is bound to proteins (mostly albumin), roughly half is ionized and the rest is complexed with phosphate and citrate. PTH and 1,25-dihydroxyvitamin D regulate it, and calcitonin has a weaker effect. Total calcium changes by about 0.8 mg/dL per 1 g/dL change in albumin, but albumin-based correction is only an estimate, and ionized calcium is preferred when albumin, acid-base status or protein binding is altered. Labcorp uses a colorimetric method and Mayo Clinic Laboratories a photometric one. EDTA, citrate and oxalate interfere. Hyperparathyroidism (most common in outpatients) and malignancy (more common in hospitalized patients) are the leading causes of hypercalcemia. The Merck Manual notes that calcium is rarely above 12 mg/dL in hyperparathyroidism and that a value above 13 mg/dL suggests cancer. Intervals vary by lab: for ages 18 to 59, Labcorp prints 8.7–10.2 mg/dL and Mayo Clinic Laboratories 8.6–10.0, while the Merck Manual gives 8.8–10.4. Critical limits are below 6.0 or above 13.0 mg/dL at ARUP and 6.0 or lower and 13.0 or higher at Quest.
LOINC 17861-6 (primary), 2000-8, 49765-1. Specimen: serum-or-plasma.
Sources
- Calcium (test 001016), Labcorp
- Calcium, Total, Serum (test ID CA), Mayo Clinic Laboratories
- Overview of Disorders of Calcium Concentration, Merck Manual Professional Edition (2025)
- Hypercalcemia, Merck Manual Professional Edition (2025)
- Hypocalcemia, Merck Manual Professional Edition (2025)
- Critical Values List (CORP-APPEND-0104A, Rev. 46), ARUP Laboratories (2026)
- Quest Diagnostics Priority Result Reporting Policy (Client Synopsis), Quest Diagnostics (2025)
- Diagnostic Laboratories: Critical Values, Houston Methodist
- Calcium (PubChem CID 5460341), PubChem, National Library of Medicine
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.