What isPrimary: Elevated
Secondary: Decreased
Tertiary: Elevated

What isIn states of volume overload, chronic illness, malnutrition the total serum protein is often reduced. This results in low total calcium levels since ~45% of calcium in the body is bound to proteins, mainly albumin.

Most are dehydrated so aggressive fluid resuscitation, >200 mL/hr to promote renal excretion of calcium as well as restore intravascular volume.
Glucocorticoids decrease intestinal absorption of calcium, increase renal excretion, and inhibit osteoclast-activating factor. They are not effective for cancer induced hypercalcemia.
Bisphosphonates inhibit osteoclast activity, thus reducing calcium levels.

C
Parathyroid carcinoma is a rare entity and is rarely diagnosed preoperatively. However, a high index of suspicion should exist for a patient with a palpable neck mass and hypercalcemia (>14 mg/dL). Papillary carcinoma is the most common of the malignant tumors of the thyroid, accounting for approximately 50% of malignant thyroid tumors in adults and 75% in children. However, a palpable mass and associated hypercalcemia is not the usual presentation for this thyroid neoplasm. Both parathyroid adenoma and hyperplasia can certainly present with hypercalcemia. The abnormal glands are rarely if ever palpable. The incidence of anaplastic carcinoma of the thyroid ranges from 7% to 15%. A rapidly growing mass, dyspnea, hoarseness, pain, dysphagia, cough, weight loss, or a combination of symptoms allowed the diagnosis to be made preoperatively in 94% of patients in one 250series; 29% had pulmonary or bone metastases at the time of initial presentation. Although a patient could present with hypercalcemia and a palpable neck mass, this patient is essentially asymptomatic, making parathyroid carcinoma the most likely diagnosis.

C
Severly elevated calcium levels represent a hypercalcemic crisis. Hypercalcemis crisis is a life-threatening emergency. Patients with calcium levels greater than 14 mg/dL or symptomatic patients with calcium levels greater than 12 mg/dL should be immediately and aggressively treated because severe hypercalcemia poses a risk of renal failure as well as severe central nervous system manifestations including coma. In addition, it leads to a shortening of the QT interval, tachycardias, and an increased sensitivity to digitalis. Treatment is divided into fast- and slow-acting modules. Fast-acting modules include those that induce a calciuresis (IV fluids), those that prevent bone resorption (bisphosphonates), and those that extract calcium (hemodialysis). Slow-acting measures prevent GI absorption of calcium (prednisone, reduced Vit D intake). The first-line therapy for hypercalcemic crisis involves rehydration with normal saline. Urine output should be kept at more than 100 mL/hr. Once urine output is established, diuresis with furosemide is instituted. Furosemide works by increasing renal calcium clearance. If these methods are not successful, then additional fast-acting modalities should be used.