When you think of calcium, you probably think of bones and teeth, where 99% of your body's calcium is stored. However, the remaining 1% circulates in your blood, where it is vital for muscle contractions, nerve signaling, and blood clotting.
Your body guards the calcium level in your blood fiercely. If your blood calcium drops, your body will literally pull calcium out of your bones to keep the blood levels stable. Therefore, a blood calcium test is not a good way to check for osteoporosis; instead, it checks for problems with the organs and glands that regulate calcium.
Typical Total Calcium reference ranges (mg/dL)
| Adults | 8.5 – 10.2 | Ranges vary slightly by lab |
|---|---|---|
| Children | Higher than adults | Due to active bone growth |
Total calcium measures both free calcium and calcium bound to proteins (like albumin).
What high calcium (Hypercalcemia) means
High calcium in the blood is called hypercalcemia. It is not caused by drinking too much milk or eating too much cheese. The most common cause is overactive parathyroid glands (hyperparathyroidism). These four tiny glands in your neck control calcium levels, and if one becomes overactive, it pumps too much calcium into the blood.
Mildly high calcium often causes no symptoms and is found on routine screening. More significantly elevated levels can cause a cluster of symptoms sometimes remembered as 'stones, bones, groans, and moans': kidney stones, bone pain, abdominal cramps, and fatigue or confusion.
What low calcium (Hypocalcemia) means
Low calcium is called hypocalcemia. The most common reason for a low total calcium result on a lab report is actually low albumin (a protein in the blood). Because much of the calcium in your blood is bound to albumin, if albumin is low, total calcium looks low, even though the 'free' active calcium is normal.
True low calcium can be caused by vitamin D deficiency, kidney disease, or underactive parathyroid glands. Symptoms of true low calcium include muscle cramps, tingling in the lips and fingers, and muscle spasms.
When to actually worry — and when not to
- A calcium level above 12.0 mg/dL or below 7.0 mg/dL is usually considered critical and requires prompt medical attention.
- If you have a high calcium result along with severe abdominal pain, confusion, or extreme thirst and urination, contact your doctor.
- A consistently high calcium level, even if mild, should always be investigated to rule out parathyroid issues.
Common questions
Does a normal calcium blood test mean my bones are healthy?
No. Your body prioritizes keeping blood calcium normal over keeping bones dense. If you aren't getting enough calcium, your body will steal it from your bones to keep the blood level normal. To check bone health, you need a DEXA scan, not a blood test.
What is 'ionized calcium'?
Total calcium measures all the calcium in your blood. Ionized calcium measures only the 'free' calcium that is not attached to proteins. If your total calcium is abnormal, your doctor might order an ionized calcium test to get a more accurate picture of the active calcium in your body.
One value never tells the whole story.
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Upload your reportMedical disclaimer: This article is for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Reference ranges vary between laboratories — always compare your result to the range on your own report, and consult a qualified healthcare professional about your results and any symptoms.