Calcium is a very important substance for the human body. Among other important functions, calcium is used by the nervous system to transmit nerve impulses and by the muscular system to help muscles contract. Approximately 99 percent of the total calcium in the human body is present in the bones; the remainder is present in the blood. Calcium levels in the blood must be kept within a very narrow range to be considered normal. When this limit is exceeded, a person can be plagued by various symptoms.
Hypercalcaemia is the term doctors use to describe the condition wherein amounts of calcium in the blood are higher than normal. The average level of calcium in the blood should be 9 to 10.5 mg/dL (milligrams per deciliter). High blood calcium exists when the amount reaches 12.0 mg/dL. A medical emergency can occur when calcium levels in the blood increase to a very high level. The individual can suffer cardiac arrest or go into a coma. In such extreme cases the amount of calcium has reached 15 to 16 mg/dL. This condition would be called severe hypercalcaemia.
A person who has high blood calcium will experience unusual signs in his digestive system, heart, muscles, bones and kidneys. High blood calcium by itself can cause appetite loss and, therefore, weight loss. Individuals will also suffer constipation. Nausea and vomiting will also occur, and this could leave the individual constantly thirsty. In terms of the heart, a person with high blood calcium would suffer hypertension and irregular heart rhythms or a lowered heart rate. Other cardiac symptoms would be detected in an EKG. People who have this condition often feel inexplicably exhausted or lethargic. They may also have a hard time concentrating, and they can easily become confused. Moreover, sufferers notice that their bones have weakened, and they frequently experience bone pain. Finally, high blood calcium can lead sufferers to urinate more often than normal. It can also lead to the formation of kidney stones, and, in more severe cases, it can result in kidney failure.
Humans have four parathyroid glands that secrete parathyroid hormone (PTH). This hormone raises the concentration of calcium in the blood as necessary. Sometimes one of these glands develops a benign tumor (non-cancerous). The presence of such a tumor would cause the gland to malfunction and keep producing PTH regardless of the level of calcium in the blood. This hormone disorder is called hyperparathyroidism. It is estimated that 98 percent of people who exhibit hypercalcaemia have hyperparathyroidism as well.
Other than dysfunctional parathyroid glands, certain types of cancer can cause high blood calcium. Some types of cancers spread to the bone and consume the center of the bone, thus releasing more calcium into the blood. There are also certain types of malignant tumors that can produce a hormone similar enough to PTH that it "fools" the bones into releasing more calcium. This tumor-secreted hormone is called parathyroid-related-peptide. These cancer-related occurrences regarding high blood calcium mostly occur when the cancer is already very advanced. Another possible but very rare cause of hypercalcaemia is a surplus of Vitamin D in the body. This particular vitamin helps our intestines absorb calcium from the food we eat. Theoretically, a person who takes Vitamin D supplements excessively will increase the total amount of calcium in his body. But healthy parathyroid and thyroid glands could easily compensate for this surplus and control the amount that goes into the blood. Much rarer diseases or disorders that cause high blood calcium include sarcoidosis, or an overactive immune system; Paget's disease, or chronic and abnormal bone growth in specific areas; and Addison's disease, or the failure of the adrenal glands.
Broad scope tests, such as the Comprehensive Metabolic Panel and the Basic Metabolic Panel, can evaluate various conditions relating to the total amount of calcium in the blood. When the level of calcium tests higher than normal, more targeted tests will be done. One of these is a test to measure ionized calcium and the amount of PTH. Ionized calcium is the calcium in the blood that is not bound to proteins. Determining the amount of ionized calcium and PTH can help assess whether there is any disorder in the parathyroid gland. Test measurements of urine calcium can diagnose any problems with the excretion of calcium by the kidneys. Measurements of Vitamin D, phosphorous and magnesium can help determine other metabolic deficiencies or excesses.