Blood Ca (Calcium) Level
Blood Ca (Calcium) Level
Calcium is the most prevalent mineral in the body. It is a major component of bones and teeth, and is also important in the functioning of the muscles, nervous system, heart, and the blood clotting system.
The bones are the body’s major storage compartment for calcium. About 99% of the body’s total calcium is located in bone. In the blood, calcium is either free or bound to the protein albumin. The bound calcium is essentially inactive; the free calcium is considered biologically active. Calcium is obtained through the diet, and requires the presence of a normal quantity of vitamin D for efficient absorption from the intestine into the bloodstream.
Hormones involved in calcium metabolism include parathyroid hormone and calcitonin. Parathyroid hormone is released by the parathyroid glands, which are located behind the thyroid gland in the mid-neck. When blood calcium levels are low, the parathyroid glands are stimulated to produce and release parathyroid hormone. Parathyroid hormone acts to induce the release of calcium from bone. Parathyroid hormone is also active in the kidney, and is involved in keeping calcium from being excreted out of the body. Parathyroid hormone also stimulates the kidney to convert vitamin D into its active form, calcitriol, which is paramount to the intestinal absorption of calcium. Calcitonin is produced by special cells (parafollicular cells) in the thyroid gland. Calcitonin is involved in prompting bone to resorb calcium from the bloodstream.
A blood calcium level may be drawn as part of a general metabolic panel, during a routine physical examination. A blood calcium level may also be ordered if there are concerns regarding arrhythmias of the heart; problems with the muscles or nervous system; kidney stone; pancreatitis; infection; evidence of kidney disease; concerns about intestinal absorption; or problems with blood clotting. The test may also be useful if the patient has signs of too much blood calcium (hypercalcemia) or low blood calcium (hypocalcemia). Signs of hypercalcemia can include abnormal tiredness, weakness, decreased appetite, nausea and vomiting, constipation, excessive thirstiness, increased urination. Signs of hypocalcemia can include numbness or a tingling sensation in the hands and feet and around the mouth, muscle spasms, or abdominal cramps. Blood calcium levels may also be monitored regularly in patients who have conditions that may cause abnormal calcium levels, such as cancers of the breast, lung, head and neck, kidney, and multiple myeloma; malnutrition (including due to anorexia or other eating disorders); thyroid disease; intestinal disorders; kidney disease; history of kidney transplant; treatment with calcium or vitamin D supplements.
Patients who use calcium supplements or vitamin D should stop taking them for the twenty-four hours prior to their blood test.
This test requires blood to be drawn from a vein (usually one in the forearm), generally by a nurse or phlebotomist (an individual who has been trained to draw blood). A tourniquet is applied to the arm above the area where the needle stick will be performed. The site of the needle stick is cleaned with antiseptic, and the needle is inserted. The blood is collected in vacuum tubes. After collection, the needle is withdrawn, and pressure is kept on the blood draw site to stop any bleeding and decrease bruising. A bandage is then applied.
There are no restrictions on diet or physical activity, either before or after the blood test.
As with any blood tests, discomfort, bruising, and/or a very small amount of bleeding is common at the puncture site. Immediately after the needle is withdrawn, it is helpful to put pressure on the puncture site until the bleeding has stopped. This decreases the chance of significant bruising. Warm packs may relieve minor discomfort. Some individuals may feel briefly woozy after a blood test, and they should be encouraged to lie down and rest until they feel better.
Calcitonin— A hormone made by the thyroid gland. Calcitonin is involved in regulating levels of calcium and phophorus in the blood.
Hypercalcemia— High levels of blood calcium.
Hypocalcemia— Low levels of blood calcium.
Pancreatitis— Inflammation of the pancreas.
Parathyroid hormone— A hormone that is secreted by the parathyroid glands. Parathyroid hormone is involved in the regulation of calcium levels in the blood.
Basic blood tests, such as blood calcium levels, do not carry any significant risks, other than slight bruising and the chance of brief dizziness.
The blood calcium level can be determined by measuring the total blood calcium (the calcium that is bound to the protein albumin and the calcium that is free in the blood serum), or by measuring the free (ionized) calcium. Although measuring the total blood calcium is generally easier and usually sufficient in most patients, some patients have conditions that will affect these results; in these patients, it is important to measure the free calcium. Such patients include those who are extremely, critically ill, patients who are getting blood transfusions or large quantities of intravenous fluids or nutrition; patients who will undergo or have recently undergone major surgery, and patients who do not have normal levels of blood protein (albumin).
Normal results for a total blood calcium level in adults ranges from 0.0-103.5 milligrams per deciliter (mg/dL) or 2.25-2.75 millimoles per liter (mmol/L). Children have higher calcium levels, because their bones are in such a high-growth phase. Normal total blood calcium levels in children range from 7.6-10.8 mg/dL or 1.9-2.7 mmol/L. A normal free or ionized calcium level in adults is 4.65-5.28 mg/dL.
High blood calcium levels may be due to:
- prolonged bedrest;
- hyperparathyroidism (overactive parathyroid glands);
- kidney disease;
- cancer in the bones;
- too much calcium, vitamin D, or vitamin A in the diet; excessive intake of dairy products; excessive intake of antacids or supplements;
- Paget’s disease;
- Addison’s disease; or
- chronic kidney or liver diseases.
Low blood calcium levels may be due to:
- hypoparathyroidism (underactive parathyroid glands);
- intestinal problems that interfere with appropriate absorption of nutrients;
- bone disorders;
- kidney disease;
- low serum albumin (hypoalbuminemia);
- low magnesium;
- pregnancy; or
- advanced age in men.
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Goldman L., D. Ausiello, eds. Cecil Textbook of Internal Medicine, 23rd ed. Philadelphia: Saunders, 2007.
McPherson R. A., and M. R. Pincus, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods, 21st ed. Philadelphia: Saunders, 2006.
Medical Encyclopedia. Medline Plus. U.S. National Library of Medicine and the National Institutes of Health. January 2, 2008. http://www.nlm.nih.gov/medlineplus/encyclopedia.html (February 10, 2008).
American Association for Clinical Chemistry, 1850 K Street, NW, Suite 625, Washington, DC, 20006, (800) 892-1400, http://www.aacc.org.
Rosalyn Carson-DeWitt, M.D.