A blood calcium level that is more than 10.4 milligrams per deciliter is high and suggests the presence of hypercalcemia, explains The Merck Manual Professional Edition. Common causes of this condition include hyperparathyroidism, vitamin D toxicity and cancer.
In some cases hypercalcemia does not cause symptoms and the abnormality is found on a routine blood test. When symptoms are present, they include constipation, anorexia, nausea, vomiting, abdominal pain, ileus, urinary frequency, an urge to urinate at night and excessive thirst, according to The Merck Manual Professional Edition. Blood calcium levels greater than 12 milligrams per deciliter may cause additional symptoms, such as emotional instability, confusion, delirium, psychosis, stupor and coma.