Hypercalcemia, or high levels of calcium in the blood, is defined by the Merck Manual as a calcium concentration greater than 10.4 milligrams per deciliter, or mg/dL. Hypercalcemia may or may not cause any signs or symptoms. The most common symptoms when present include fatigue, impaired concentration, an increase in frequency of urination, decreased appetite, thirst, nausea, vomiting and constipation. The Merck Manual notes that levels of calcium greater than 18 mg/dL can result in kidney failure, shock and even death.
One of the functions of the kidneys is to remove excess calcium from the body in the urine. High levels of calcium can put extra stress on the kidneys and cause it to lose the ability to remove excess calcium. Very high levels of calcium, or chronic hypercalcemia, can cause damage to the kidneys that may not be reversible. Signs and symptoms related to ineffective kidney function include kidney stones, increased frequency of urination, increased urination at night, flank pain and increased thirst. Increased frequency of urination may be caused by the deposition of calcium in the kidney, which can result in nephrogenic diabetes insipidus, a condition in which the kidneys are unable to concentrate urine. Increased excretion of urine, in turn, leads to dehydration and thirst. According to the Cleveland Clinic, 20% of those with hypercalcemia experience increased thirst and urination related to nephrogenic diabetes insipidus.
Gastrointestinal manifestations include abdominal pain, constipation, nausea, vomiting and decreased appetite. These symptoms are caused by dehydration induced by increased urination. Dehydration is worsened by these precipitating factors. Hypercalcemia may also increase the production of stomach acid, which can exacerbate nausea, vomiting and decreased appetite.
Calcium is needed by the heart to beat properly, however too much calcium can cause an abnormal beating of the heart known as an arrhythmia. Hypercalcemia can also result in hypertension and cardiovascular calcification. Hypertension occurs when the kidneys become damaged from high levels of calcium, and lose the ability to regulate blood pressure properly. Hypertension may also be caused by constriction of blood vessels from hypercalcemia.
According to the Linus Pauling Institute, calcium is needed for the transmission of nerve signals and contraction of muscles. Muscular symptoms include muscle twitches, atrophy of the muscles and weakness. Psychological manifestations include fatigue, depression, anxiety, irritability and impaired concentration. Confusion, dementia, memory loss and coma can occur with calcium levels greater than 12 mg/dL, notes the Merck Manual. Headaches may also be present and are a result of dehydration.
Skeletal symptoms include bone pain, height loss, fractures, increase in the curvature of the spine and bowing of the shoulders. These symptoms may be caused by calcium secreting tumors that have metastasized to the bone or from decrease in bone mass.