This article discusses the test used to measure the amount of ionized calcium in blood.
How the Test is Performed
A blood sample is needed. Most of the time blood is drawn from a vein located on the inside of the elbow or the back of the hand.
How to Prepare for the Test
You should not eat or drink for at least 6 hours before the test.
Many medicines can interfere with blood test results.
- Your health care provider will tell you if you need to stop taking any medicines before you have this test.
- DO NOT stop or change your medicines without talking to your provider first.
Why the Test is Performed
Your provider may order this test if you have signs of kidney or parathyroid disease. The test may also be done to monitor the progress and treatment of these diseases.
Most of the time, blood tests measure your total calcium level. This looks at both ionized calcium and calcium attached to proteins. You may need to have a separate ionized calcium test if you have factors that increase or decrease total calcium levels. These may include abnormal blood levels of albumin or immunoglobulins.
Normal Results
- Children: 4.8 to 5.3 milligrams per deciliter (mg/dL) or 1.20 to 1.32 millimoles per liter (millimol/L)
- Adults: 4.8 to 5.6 mg/dL or 1.20 to 1.40 millimol/L
Normal value ranges may vary slightly among different laboratories. Talk to your health care provider about the meaning of your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
What Abnormal Results Mean
Higher-than-normal levels of ionized calcium may be due to:
- Decreased levels of calcium in the urine from an unknown cause
- Hyperparathyroidism
- Hyperthyroidism
- Milk-alkali syndrome
- Multiple myeloma
- Paget disease
- Sarcoidosis
- Thiazide diuretics
- Thrombocytosis (high platelet count)
- Tumors
- Vitamin A excess
- Vitamin D excess
Lower-than-normal levels may be due to:
- Hypoparathyroidism
- Malabsorption
- Osteomalacia
- Pancreatitis
- Renal failure
- Rickets
- Vitamin D deficiency
FAQ
What does a calcium blood test check for?
- A blood calcium test is ordered to screen for, diagnose, and monitor a range of conditions relating to the bones, heart, nerves, kidneys, and teeth. The test may also be ordered if a person has symptoms of a parathyroid disorder, malabsorption, or an overactive thyroid.
What does high calcium levels mean in a blood test?
- Hypercalcemia is a condition in which the calcium level in your blood is above normal. Too much calcium in your blood can weaken your bones, create kidney stones, and interfere with how your heart and brain work. Hypercalcemia is usually a result of overactive parathyroid glands.
What are normal calcium levels in the blood?
- Normal values range from 8.5 to 10.2 mg/dL (2.13 to 2.55 millimol/L). Normal value ranges may vary slightly among different laboratories.
What does low calcium mean in a blood test?
- In hypocalcemia, the calcium level in the blood is too low. A low calcium level may result from a problem with the parathyroid glands, as well as from diet, kidney disorders, or certain drugs.
What is the most common cause of high calcium levels?
- The most common cause of high calcium blood levels is excess PTH released by the parathyroid glands. This excess occurs due to: An enlargement of one or more of the parathyroid glands.
What are the symptoms of calcium deficiency in adults?
- Low levels of calcium can cause extreme fatigue, which involves a lack of energy and an overall feeling of sluggishness. It can also lead to insomnia. Fatigue associated with a calcium deficiency can also involve lightheadedness, dizziness, and brain fog — characterized by a lack of focus, forgetfulness, and confusion.

