PTH (Parathyroid Hormone)

What is PTH

PTH (parathyroid hormone) is a hormone produced by the parathyroid glands that regulates calcium and phosphate metabolism in the body. Four small parathyroid glands are located near the thyroid gland in the neck.

When blood calcium levels fall, the parathyroid glands increase PTH production. PTH acts in three ways: it stimulates calcium resorption from bones, increases calcium reabsorption in the kidneys, and indirectly (via vitamin D) increases calcium absorption in the intestine.

PTH is tested together with calcium, phosphate, and vitamin D — only all together do they provide a complete picture.

Reference ranges

Typical range: 15–65 pg/mL (picograms per millilitre). In SI units — approximately 1.6–6.9 pmol/L.

The laboratory's reference range is most important, as different test methods may have slightly different norms. Important: biotin supplements can interfere with the PTH assay and give falsely low results — inform your doctor if you are taking biotin.

Why PTH may be elevated

• Primary hyperparathyroidism — the most common cause, when one or more parathyroid glands produce too much PTH (usually due to an adenoma). Blood calcium is also elevated.
• Vitamin D deficiency — a common cause of secondary hyperparathyroidism. When vitamin D is deficient, intestinal calcium absorption decreases, and the parathyroid glands compensatorily increase PTH. Calcium is usually normal or low.
• Chronic kidney disease — the kidneys inadequately activate vitamin D and fail to excrete phosphate, which stimulates PTH production.
• Dietary calcium deficiency — insufficient calcium intake over time increases PTH.

Why PTH may be low

• Hypoparathyroidism — the most common cause is surgical (the parathyroid glands are accidentally damaged during thyroid surgery). Blood calcium is low.
• Autoimmune hypoparathyroidism — a rare condition in which the body damages parathyroid gland cells.
• Hypomagnesaemia — severely low magnesium can block PTH secretion.
• Hypercalcaemia without PTH elevation — when calcium is elevated due to other causes (e.g., malignancy), PTH is physiologically suppressed.

What to do next

If PTH is elevated, the first step is to check vitamin D and calcium levels. This helps distinguish primary hyperparathyroidism (high PTH + high calcium) from secondary (high PTH + low or normal calcium due to vitamin D deficiency).

If PTH is elevated due to vitamin D deficiency, vitamin D supplementation may normalise PTH levels. Your doctor may recommend:

• Testing 25-OH vitamin D, ionised calcium, and phosphate.
• Bone density measurement (if PTH has been elevated for a long time).
• Assessment of kidney function.

Monitoring over time

Monitoring PTH is important when treating vitamin D deficiency — a falling PTH indicates that supplementation is working. In primary hyperparathyroidism, PTH trends help track disease progression.

A history of kidney stones together with elevated PTH is an important signal for your doctor, as hyperparathyroidism is one of the causes of kidney stones.

Questions for your doctor

1. Is my elevated PTH related to vitamin D deficiency or primary hyperparathyroidism? 2. What vitamin D level should I aim for to normalise PTH? 3. Do I need a bone density scan? 4. Could my kidney function be related to my elevated PTH? 5. Should I retest PTH periodically, and how often?

*This is not medical advice. Please consult your doctor regarding any health decisions.*