The intact parathyroid hormone (iPTH) test is crucial post-thyroidectomy in assessing parathyroid gland health by measuring intact parathyroid hormone levels. Elevated iPTH signals potential hyperparathyroidism and calcium imbalances, while low levels indicate hypoparathyroidism. This test aids in diagnosing and managing parathyroid disorders, which are vital for post-operative care to maintain proper mineral balance.