After recognition, primary hyperparathyroidism should be proved or excluded.In extreme cases of primary hyperparathyroidism, removal of the parathyroid gland after surgical neck exploration is the only way to avoid death. The diagnostic program should be performed within hours, in parallel with measures to lower serum calcium. Treatment of choice for acutely lowering calcium is extensive hydration and calcitonin, as well as bisphosphonates (which have effect on calcium levels after one or two days). Causes
Primary hyperparathyroidism and malignancy account for about 90% of cases of hypercalcaemia.Causes of hypercalcemia can be divided into those that are PTH dependent or PTH independent. Parathyroid function
Primary hyperparathyroidism
Solitary parathyroid adenoma
Primary parathyroid hyperplasia
Parathyroid carcinoma
Multiple endocrine neoplasia (MEN1 & MEN2A)
Familial isolated hyperparathyroidism
Lithium use
Familial hypocalciuric hypercalcemia/familial benign hypercalcemia

Cancer
Solid tumour with metastasis (e.g. breast cancer or classically squamous cell carcinoma, which can be PTHrP-mediated)
Solid tumour with humoral mediation of hypercalcaemia (e.g. lung cancer, most commonly non-small cell lung cancer or kidney cancer, phaeochromocytoma)
Haematologic cancers (multiple myeloma, lymphoma, leukaemia)
Ovarian small cell carcinoma of the hypercalcemic type

Vitamin-D disorders
Hypervitaminosis D (vitamin D intoxication)
Elevated 1,25(OH)2D (see calcitriol under Vitamin D) levels (e.g. sarcoidosis and other granulomatous diseases such as tuberculosis, berylliosis, histoplasmosis, Crohns disease, and granulomatosis with polyangiitis)
Idiopathic hypercalcaemia of infancy
Rebound hypercalcaemia after rhabdomyolysis

High bone-turnover
Hyperthyroidism
Multiple myeloma
Prolonged immobilization
Pagets disease
Thiazide use
Vitamin A intoxication

Kidney failure
Tertiary hyperparathyroidism
Aluminium intoxication
Milk-alkali syndrome

Other
Acromegaly
Adrenal insufficiency
Zollinger–Ellison syndrome
Williams Syndrome

Diagnosis
Diagnosis should generally include either a calculation of corrected calcium or direct measurement of ionized calcium level and be confirmed after a week. This is because either high or low serum albumin levels does not show the true levels of ionised calcium.
Calcitonin blocks bone resorption and also increases urinary calcium excretion by inhibiting calcium reabsorption by the kidney
Usually used in life-threatening hypercalcaemia along with rehydration, diuresis, and bisphosphonates
Helps prevent recurrence of hypercalcaemia
Dose is 4 international units per kilogram via subcutaneous or intramuscular route every 12 hours, usually not continued indefinitely due to quick onset of decreased response to calcitonin

Other therapies
rarely used, or used in special circumstances
plicamycin inhibits bone resorption (rarely used)
gallium nitrate inhibits bone resorption and changes structure of bone crystals (rarely used)
glucocorticoids increase urinary calcium excretion and decrease intestinal calcium absorption
no effect on calcium level in normal or primary hyperparathyroidism
effective in hypercalcaemia due to osteolytic malignancies (multiple myeloma, leukaemia, Hodgkins lymphoma, carcinoma of the breast) due to antitumour properties
also effective in hypervitaminosis D and sarcoidosis
dialysis usually used in severe hypercalcaemia complicated by kidney failure. Supplemental phosphate should be monitored and added if necessary
phosphate therapy can correct the hypophosphataemia in the face of hypercalcaemia and lower serum calcium

Other animals
Research has led to a better understanding of hypercalcemia in non-human animals. Often the causes of hypercalcemia have a correlation to the environment in which the organisms live. Hypercalcemia in house pets is typically due to disease, but other cases can be due to accidental ingestion of plants or chemicals in the home. Outdoor animals commonly develop hypercalcemia through vitamin D toxicity from wild plants within their environments. Household pets
Household pets such as dogs and cats are found to develop hypercalcemia. It is less common in cats, and many feline cases are idiopathic.