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Diagnosis

If detailed history and examination does not narrow down the differential diagnoses, further laboratory investigations are performed. Intact PTH (iPTH, biologically active parathyroid hormone molecules) is measured with immunoradiometric or immunochemoluminescent assay. Elevated (or high-normal) iPTH with high urine calcium/creatinine ratio (more than 0.03) is suggestive of primary hyperparathyroidism, usually accompanied by low serum phosphate. High iPTH with low urine calcium/creatinine ratio is suggestive of familial hypocalciuric hypercalcemia. Low iPTH should be followed up with Parathyroid hormone-related protein (PTHrP) measurements (though not available in all labs). Elevated PTHrP is suggestive of malignancy. Normal PTHrP is suggestive of multiple myeloma, vitamin A excess, milk-alkali syndrome, thyrotoxicosis, and immobilisation. Elevated Calcitriol is suggestive of lymphoma, sarcoidosis, granulomatous disorders, and excessive calcitriol intake. Elevated calcifediol is suggestive of vitamin D or excessive calcifediol intake.