Parathyroid Hormone (PTH)

The Parathyroid Hormone (PTH) test measures the amount of PTH in the blood. PTH is a hormone produced by the parathyroid glands that helps regulate calcium and phosphate levels in the blood and bones. This test is commonly used to evaluate parathyroid gland function and diagnose the causes of abnormal calcium levels.

1. What Is PTH?

• PTH is secreted by four small parathyroid glands located behind the thyroid gland.

• It plays a critical role in maintaining calcium balance by:

  - Increasing calcium absorption from the intestine (via vitamin D activation)

  - Stimulating calcium release from bones

  - Reducing calcium excretion by the kidneys

• PTH also lowers phosphate levels by increasing phosphate excretion in urine.

2. Why Is the PTH Test Performed?

This test is used to:

• Diagnose hyperparathyroidism or hypoparathyroidism.

• Investigate the cause of high or low calcium levels.

• Monitor treatment in individuals with parathyroid disorders or chronic kidney disease.

• Evaluate bone health and calcium metabolism.

3. PTH Reference Range

• Normal range: 10 – 65 pg/mL (varies by lab and testing method)

• Interpretation depends on corresponding calcium and vitamin D levels.

4. Interpreting PTH Results

🔹 High PTH (Hyperparathyroidism):

• Primary: Due to parathyroid gland overactivity (e.g., benign tumor).

• Secondary: Response to low calcium (e.g., vitamin D deficiency, chronic kidney disease).

• Tertiary: Seen in chronic renal failure with long-standing secondary hyperparathyroidism.

🔹 Low PTH (Hypoparathyroidism):

• May result from parathyroid gland damage, autoimmune disorders, or low magnesium levels.

• Leads to low calcium and high phosphate levels.

5. What Can Affect PTH Levels?

• Blood calcium and phosphate levels

• Vitamin D status and kidney function

• Medications (e.g., diuretics, lithium, calcium or vitamin D supplements)

• Surgery involving the thyroid or parathyroid glands

6. How Is the Test Performed?

• A blood sample is drawn, often in conjunction with calcium and vitamin D levels.

• Fasting may be required, especially if calcium or phosphorus is being tested.

7. When to See a Doctor

🚨 Contact your healthcare provider if you:

• Have symptoms of calcium imbalance (e.g., muscle cramps, bone pain, fatigue, tingling).

• Show abnormal blood calcium, phosphorus, or vitamin D levels.

• Are being evaluated for kidney disease, osteoporosis, or parathyroid disorders.

🔹 Key Takeaways

✅ PTH is essential for regulating calcium and phosphate in the body.

✅ Abnormal levels can point to parathyroid dysfunction or metabolic imbalances.

✅ Proper interpretation requires consideration of calcium, phosphate, and vitamin D levels.