Calcium: Normal Range, What High & Low Levels Mean

A calcium blood test — also called a serum calcium, total calcium, or Ca test — measures the total amount of calcium present in your blood at the time of the draw. Calcium is essential for much more than bone strength; your muscles need it to contract, your nerves use it to send signals, and your blood relies on it to clot properly. Because these functions are so critical, your body uses parathyroid hormone (PTH) and vitamin D to keep blood calcium levels within a very narrow, tightly regulated range. Talk with your healthcare provider about what your specific result means in the context of your overall health.

For adults aged 18 and over, the reference range established by Mayo Clinic Laboratories is 8.5 to 10.2 mg/dL. A result within this window generally suggests your body's calcium-regulating system is working as expected. Keep in mind that different laboratories may use slightly different equipment and methods, so the reference range printed on your own report is the most relevant one to look at. Results that fall just outside any reference range do not automatically signal a problem — patterns over time and your broader clinical picture matter just as much. Your healthcare provider is the right person to interpret exactly where your number stands.

When calcium rises above 10.2 mg/dL, doctors call this hypercalcemia. The most common persistent cause is primary hyperparathyroidism, where overactive parathyroid glands release too much PTH. Other causes include certain cancers — such as those involving bone metastases, multiple myeloma, or tumors that release a PTH-like protein — as well as granulomatous diseases like sarcoidosis or tuberculosis. Vitamin D toxicity from excess supplementation, prolonged immobility, certain medications like thiazide diuretics, and excessive intake of calcium combined with antacids can also push levels up. Because the list of causes is broad and some are serious, your healthcare provider needs to evaluate your specific result and history.

A calcium level below 8.5 mg/dL is called hypocalcemia. Common causes include hypoparathyroidism — low levels of PTH, which can develop after thyroid or neck surgery — and vitamin D deficiency, which reduces how much calcium your gut absorbs. Chronic kidney disease can lower calcium because the kidneys play a key role in activating vitamin D and managing phosphate levels. Conditions that affect nutrient absorption, such as celiac disease or Crohn's disease, low magnesium, pancreatitis, and certain medications including bisphosphonates, denosumab, and loop diuretics can also lower levels. Identifying the underlying cause is essential for proper management, so share your full medication and health history with your healthcare provider.

High calcium can cause fatigue, weakness, nausea, vomiting, constipation, increased thirst, frequent urination, kidney stones, bone pain, abdominal pain, and difficulty concentrating or low mood. Low calcium tends to produce different sensations: muscle cramps and spasms — especially in the face, hands, and feet — numbness and tingling around the mouth and fingers (called paraesthesia), muscle twitching, dry skin, brittle nails, coarse hair, feelings of anxiety or depression, and in severe cases irregular heartbeat or seizures. Symptoms alone cannot confirm which direction your calcium has shifted, and many of these overlap with other conditions. Always discuss any new or persistent symptoms alongside your lab result with your healthcare provider.

Preparation can vary depending on whether calcium is being checked as part of a broader panel or on its own, so your best step is to ask your ordering provider or the lab whether fasting or any other preparation is needed before your specific draw. Factors like hydration, body position during the draw, and the particular laboratory running the sample can all influence results slightly. If your level came back outside the normal range of 8.5 to 10.2 mg/dL, your doctor may want to repeat the test or order additional follow-up tests to get a clearer picture. Your healthcare provider can tell you exactly what steps, if any, to take before your next test.