Symptoms of high calcium levels in a patient's blood include frequent urination, significant thirst, pain in the abdomen, vomiting and being confused, according to Mayo Clinic. Patients with hypercalcemia may also suffer from weakened muscles and bone pain, because as the calcium leaches from the patient's bones, they become weak.
Patients with overactive parathyroid glands may develop hypercalcemia, according to Mayo Clinic. Cancer and the overuse of calcium and vitamin D supplements also cause elevated calcium levels in the blood. High calcium levels can result in kidney stones and can affect a patient's heart and brain functions. The patient may become lethargic and fatigued. Those with mild hypercalcemia may not experience any symptoms.