Parathyroid Hormone (PTH) Test

The parathyroid hormone (PTH) test measures the amount of PTH in a blood sample. The test is also known as the intact PTH test or parathormone test.

PTH is made by the four parathyroid glands located behind the thyroid gland in your neck. It helps keep calcium levels in your blood within a healthy range. Calcium is an important mineral stored in your bones and teeth. It is important for the health of your nerves, muscles and heart. Abnormal levels of PTH can lead to conditions such as overactive or underactive parathyroid glands. Thus, doctors use this test to diagnose and monitor these conditions.

You may be advised to get the parathyroid hormone test if you are experiencing the following symptoms of too much calcium in the blood:

• Nausea
• Vomiting
• Stomach pain
• Increased thirst
• Kidney stones
• Fatigue
• Bone, joint, and muscle weakness

You may also be advised to get the test if you are experiencing the following symptoms of too little calcium in the blood:

• Muscle cramps and spasms
• Irregular heartbeat
• Seizures
• Dry skin
• Coarse hair

The test is also advised for the following categories of individuals:

• Individuals who already have parathyroid disorders – The test is generally done to find out whether parathyroid problems are causing abnormal calcium levels in the blood. It is also done to check how the treatment is working.
• Individuals with chronic kidney disease (CKD) – The test is used to monitor individuals who have been diagnosed with CKD.
• Individuals with osteoporosis – The test can help in finding out the underlying cause of osteoporosis (a condition that causes your bones to break easily).

The parathyroid hormone test can be used with other tests to help diagnose certain conditions, such as:

• Primary hyperparathyroidism – This is a condition in which the body produces too much PTH, causing calcium levels in the blood to become too high.
• Secondary hyperparathyroidism – This condition occurs due to long-term kidney disease, calcium, or vitamin D deficiency, resulting in raised PTH levels. The body has high levels of PTH because calcium levels are low in the blood. This is usually a compensatory response to chronic kidney disease, vitamin D deficiency, or calcium deficiency, leading to elevated PTH levels.
• Hypoparathyroidism – This is a condition in which the body produces too little PTH, resulting in low blood calcium levels.
• Benign tumour of the parathyroid glands – This is a non-cancerous tumour, also called a parathyroid adenoma. It is the most common cause of high PTH levels in the body.
• Parathyroid cancer – This is a rare cancer that occurs in people in their forties and fifties, affecting one of the four parathyroid glands.
• Hyperplasia of parathyroid glands – This means that your parathyroid glands have become larger than normal.
• Multiple endocrine neoplasia – This is a group of conditions that causes growths or tumours to develop in one or more of your hormone-producing (endocrine) glands.

What to Expect Before the Parathyroid Hormone (PTH) Test

No fasting is required for a standalone parathyroid hormone (PTH) test. You can eat and drink normally. However, if it is part of a broader package that includes fasting tests, your doctor may advise fasting for 8-12 hours. Avoid strenuous exercise for 24 hours before the test, as intense physical activity can temporarily raise parathyroid hormone (PTH) levels and affect interpretation. Always inform your doctor about any ongoing medications.

What to Expect During the Blood Collection

A phlebotomist cleans the skin with an antiseptic, then places an elastic band around your upper arm to make the veins easier to access. A small needle is inserted into the vein; you may feel a brief pinch. Blood is collected into a labelled tube in under a minute.

What to Expect After the Parathyroid Hormone (PTH) Test

A small cotton swab and bandage are placed over the site to stop any minor bleeding. You can return to normal activities immediately. Minor bruising is normal and disappears quickly. If dizzy, sit and rest for a few minutes.

In the PTH test, the primary parameter being measured is:

• The level of parathyroid hormone in a sample of blood.

The PTH normal range is indicated in the table below:

The table below provides a general interpretation of the parathyroid hormone test results based on whether the levels are low or high.

Like other medical tests, this test also has certain risks and limitations.

Risks:

The test is generally safe and involves little risk. You may feel slight pain when the needle is inserted or mild bruising afterwards, which usually resolves within a few days.

Limitations:

• A calcium blood test is generally needed along with a PTH test to interpret the results.
• You may need to fast for a few hours before the test or take it at a specific time of the day. Ask your doctor for proper advice on this.

Depending on your symptoms and results, your doctor might recommend the following tests to better understand your condition:

• Calcium blood test
• Calcium urine test
• Vitamin D test
• Phosphate blood test
• Phosphate urine test
• Creatinine test
• Antinuclear antibody test
• Autoantibody test