The laboratory diagnosis of hyperparathyroidism primarily focuses on simultaneous measurements of serum calcium and parathyroid hormone levels. Primary hyperparathyroidism is characterized by hypercalcemia paired with elevated or inappropriately normal circulating levels of parathyroid hormone. Complementary tests—including serum phosphate and vitamin D—assist in distinguishing primary hyperparathyroidism from secondary or tertiary hyperparathyroidism, which typically exhibits hypocalcemia or normocalcemia with elevated PTH. 24-urinary calcium excretion and calcium-to-creatinine clearance ratio are essential to differentiate primary hyperparathyroidism from familial hypocalciuric hypercalcemia. Besides being essential for the initial diagnosis of hyperparathyroidism, laboratory tests are very useful in the management of patients undergoing surgical and/or pharmacological therapy.