Causes of high calcium: Hyperparathyroidism − look also for high ionized calcium, measured or calculated. Hyperparathyroidism may coexist with other endocrine tumors (multiple endocrine adenomatosis syndromes). Carcinoma, with or without bone metastases. Humoral hypercalcemia of malignancy (HHM) (tumor-induced hypercalcemia) is seen especially in primary squamous cell carcinoma of lung, head and neck, but other important tumors include primaries in the kidney, liver, bladder, and ovary. It is probably caused by parathormone-like peptides. The most common solid tumors causing bone metastases are primaries in the breast and lung. Other neoplasms may also cause hypercalcemia. Differences between HPT and humoral hypercalcemia of malignancy include low dihydroxyvitamin D, reduced calcium absorption,1 and the presence of a nonparathyroid tumor. Alkaline phosphatase more than twice its upper limit is more suggestive of cancer than of hyperparathyroidism. Especially if there is only a brief duration of symptoms, anemia, hypoalbuminemia, and other findings suggestive of malignant disease, chloride:phosphorus ratio <29 mmol/L, chloride <100 mmol/L, high serum LD (LDH) and/or phosphorus, think first of malignant neoplasm.2 The chloride:phosphorus ratio is predominantly of value when it is <29 mmol/L, to provide evidence against a diagnosis of primary hyperparathyroidism.