Serum calcium > 10.2 mg/dL (corrected for serum albumin).

Etiology:- Hyperparathyroidism- Malignancy- Granulomatous disorders- Familial hypocalciuric hypercalcemia- Pharmacologic: Vitamin D intoxication, milk-alkali syndrome, thiazide diuretics, lithium, hyperthyroidism, Paget's disease of the bonePrimary hyperparathyroidism and hypercalcemia of malignancy account for > 90% of cases of hypercalcemia. Serum calcium is typically higher in hypercalcemia of malignancy (> 13 mg/dL), and patients therefore exhibit more severe symptoms!

Clinical features:- Bones (osteopenia, fractures, osteitis fibrosa cystica, arthralgias, myalgias)- Stones (kidney stones)- Groans (abdominal pain, nausea and vomiting, peptic ulcer disease, constipation)- Psychiatric overtones (weakness, fatigue, altered mental status)- Polyuria- Cardiac arrhythmias- Muscle weakness, paresis

Diagnosis:- Order a total/ionized calcium, albumin, phosphate, PTH.- Other workup: parathyroid hormone-related peptide (PTHrP) if malignancy is suspected, serum protein electrophoresis for multiple myeloma, bone scan to identify lytic lesions, urinary cAMP elevated in primary hyperparathyroidism, vitamin D if granulomatous disease (sarcoidosis, TB) suspected, and ECG (may show a short QT interval).

Treatment:- Mild (total calcium < 12 mg/dL): Oral hydration- Severe or symptomatic hypercalcemia (total calcium > 14 mg/dL): → IV hydration with isotonic saline→ Loop diuretics → Bisphosphonates (e.g., zoledronic acid, pamidronate), in cases of excessive bone resorption (e.g., hypercalcemia of malignancy, immobilization)→ Calcitonin- Hypercalcemic crisis (psychosis, fever, coma): IV hydration and forced diuresis