Calcium is the most abundant mineral in the human body, and it is essential for the proper function of virtually every cell. Since the body loses calcium every day, it should be included in the diet. Dietary calcium can come from some fruits and vegetables, dairy products, eggs and fish. A blood (serum) calcium test actually measures the calcium that is not in bones.
In addition to helping to build bones and teeth, calcium is essential for muscle contraction, heart function, nerve function and blood clotting.
Calcium circulates in the blood in two forms: it can either be bound to such transport proteins as albumin or be found in free, "ionized" form.
While normal blood calcium levels differ slightly from lab to lab, they usually range between 8.5 and 10.5 mg/dL (milligrams of calcium per deciliter of blood). Ionized calcium typically ranges from about 4.6 to 5.3 mg/dL
Because they are growing, children can have slightly lower or higher blood calcium than adults, with normal levels ranging from 7.6 to 10.8 mg/dL
High blood calcium (hypercalcemia) can occur for such reasons as: dehydration, an overactive parathyroid gland (hyperparathyroidism), certain cancers, getting too much calcium or vitamins A and D from the diet, abusing calcium medicines and certain diseases.
Low blood calcium (or hypocalcemia) can have various causes, including: bone problems, low levels of the blood protein albumin, inflammation of the pancreas, kidney disease, malfunction of the parathyroid gland (hypoparathyroidism) and improper absorption of foods or calcium.