Serum Calcium: Normal Range, High & Low Causes
What Calcium measures
Calcium supports bones, muscles, nerves and the heart. Your body keeps blood calcium in a narrow range using parathyroid hormone and vitamin D. Total calcium is affected by albumin, so low albumin can make calcium look low.
Calcium reference ranges
| Category | Conventional units | SI units |
|---|---|---|
| Typical adult range | 8.5 – 10.2 mg/dL | 2.12 – 2.55 mmol/L |
Clinicians may calculate an albumin-corrected calcium. 8.5 mg/dL is about 2.12 mmol/L (multiply mg/dL by 0.2495).
Need to convert units? Use the mg/dL ↔ mmol/L converter.
Common causes of a high result
- Primary hyperparathyroidism (the most common cause)
- Some cancers
- Too much vitamin D or calcium supplements
- Dehydration
- Thiazide diuretics
- Granulomatous disease such as sarcoidosis
Common causes of a low result
- Low vitamin D
- Hypoparathyroidism
- Kidney disease
- Low albumin (a false low)
- Low magnesium
- Pancreatitis
How to prepare for the test
Fasting is usually not required. Tell your clinician about calcium and vitamin D supplements.
How often to retest
Abnormal results are usually repeated and followed by parathyroid hormone and vitamin D tests.
Track Calcium over time
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Get the appFrequently asked questions
What is a normal calcium level?
About 8.5–10.2 mg/dL (2.12–2.55 mmol/L) for adults, with small differences between labs.
What does high calcium feel like?
Mild elevations often cause no symptoms. Higher levels can cause thirst, frequent urination, constipation, nausea, tiredness and confusion.
Why does my calcium look low but I feel fine?
Total calcium is influenced by albumin. If albumin is low the result can look low even when active calcium is normal, so clinicians check a corrected value.
Related tests
Sources
This page is general education and was last updated 2026-10-30. It is not a substitute for medical advice. See our editorial approach.