A calcium blood test measures the amount of calcium in your blood. Calcium is one of the most important minerals in your body. You need calcium for healthy bones and teeth. Calcium is also essential for proper functioning of your nerves, muscles, and heart. About 99% of your body's calcium is stored in your bones. The remaining 1% circulates in the blood. If there is too much or too little calcium in the blood, it may be a sign of bone disease, thyroid disease, kidney disease, or other medical conditions.

Calcium concentration, both total and free, is characterized by a high physiological variation, depending on age, sex, physiological state (eg, pregnancy), and even season (owing to the seasonal variation of vitamin D, which is directly involved in the regulation of calcium concentration). Therefore, separate reference intervals have been established according to the age and sex of the individual being tested.

Total calcium reference ranges in males are as follows:

Younger than 12 months: Not established

Age 1-14 years: 9.6-10.6 mg/dL

Age 15-16 years: 9.5-10.5 mg/dL

Age 17-18 years: 9.5-10.4 mg/dL

Age 19-21 years: 9.3-10.3 mg/dL

Age 22 years and older: 8.9-10.1 mg/dL

Total calcium reference ranges in females are as follows:

Younger than 12 months: Not established

Age 1-11 years: 9.6-10.6 mg/dL

Age 12-14 years: 9.5-10.4 mg/dL

Age 15-18 years: 9.1-10.3 mg/dL

Age 19 years and older: 8.9-10.1 mg/dL

Free (ionized) calciumreference ranges in males are as follows:

Younger than 12 months: Not established

1-19 years: 5.1-5.9 mg/dL

Age 20 years and older: 4.8-5.7 mg/dL

Free (ionized) calciumreference ranges in females are as follows:

Younger than 12 months: Not established

1-17 years: 5.1-5.9 mg/dL

Age 18 years and older: 4.8-5.7 mg/dL

Calcium (urine) reference ranges are as follows*:

Males: 25-300 mg/24-hour urine collection

Females: 20-275 mg/24-hour urine collection

Hypercalciuria: >350 mg/specimen

*Values are for persons with average calcium intake (ie, 600-800 mg/day)