Serum Parathyroid Hormone (PTH)

Function

Parathyroid Hormone (PTH) is secreted by the four parathyroid glands located in the neck. Its primary role is to maintain stable concentrations of calcium in the blood. When calcium levels drop, the parathyroid glands release PTH, which acts on the bones (releasing calcium), the kidneys (reducing calcium excretion), and the intestines (increasing calcium absorption via Vitamin D activation).

Why it is Ordered

This test is crucial for investigating the cause of abnormal calcium levels (hypocalcemia or hypercalcemia). It is also used to monitor patients with chronic kidney disease (CKD), as they often develop secondary hyperparathyroidism. Evaluating PTH helps distinguish between problems originating in the parathyroid glands versus other issues like Vitamin D deficiency or malignancy.

Associated Conditions

• Primary Hyperparathyroidism: Usually caused by a benign tumor on the gland, leading to high PTH and high calcium.
• Secondary Hyperparathyroidism: Occurs when the body raises PTH to compensate for low calcium, often due to Vitamin D deficiency or kidney failure.
• Hypoparathyroidism: Low PTH levels resulting in low calcium, often following neck surgery or autoimmune damage.