What Is a Parathyroid Hormone Blood Test?

What to Expect With This Procedure

A parathyroid hormone blood test measures the amount of parathyroid hormone in your blood. This is important for assessing multiple medical conditions, including problems with calcium in the body. You also might hear it referred to as a parathyroid hormone test, a parathyroid hormone level, or a PTH test.

Purpose of Test

What Is PTH?

Parathyroid hormone (abbreviated PTH) is a signaling molecule secreted from the parathyroid glands. These are four small glands found near the thyroid gland inside the neck.

PTH plays a critical role in the regulation of calcium in the body. This is a crucial job, as having the right amount of calcium is very important for the heart, nervous system, and other parts of your body. If the concentration of calcium in your blood gets too low or too high, it can cause serious medical problems such as an abnormal heart rhythm.

When PTH is released from the parathyroid glands, the hormone works as a signal to various parts of your body. These signals work to increase the amount of calcium in the blood in a number of different ways. For example, it causes the kidneys to eliminate less calcium through the urine. It also causes more calcium to be absorbed in your intestines.

In a healthy person, a low level of calcium in the blood triggers the release of PTH from the parathyroid glands.

This raises the amount of calcium in the blood. On the other hand, if a person’s level of calcium in the blood is a little high, the parathyroid gland starts to release less PTH. This works to bring the blood calcium back into the normal range.

When Is a PTH Test Necessary?

You may need a PTH test if your physician worries that you might have a problem causing too much or too little calcium in your blood. This might come up as a concern based on a medical problem you are having, your clinical exam, or the results of a previous medical test.

For example, a high PTH can cause too much calcium in your blood (called hypercalcemia). This might cause symptoms like excessive thirst, constipation, bone pain, and kidney stones. People with an abnormally low PTH might have too little calcium in their blood (called hypocalcemia). Such individuals might have symptoms like numbness, tingling, and muscle cramps. However, some people have an abnormal PTH without any additional symptoms.

If for whatever reason your doctor worries that your calcium level might be off, a PTH is usually ordered along with calcium and sometimes other blood tests. This needs to be investigated because having an incorrect amount of calcium in your body can cause medical problems. Also, having too low or too high calcium also might potentially be a sign of another underlying medical problem that needs to be diagnosed and treated, such as a type of cancer.

Monitoring of ongoing medical conditions is another potential reason for a PTH test. For example, someone with a condition that affects calcium regulation (like severe kidney disease) might need such a test at regular intervals. Someone who has had surgery on their parathyroid gland (or on nearby structures) is also likely to need the test.

Hypoparathyroidism and Hyperparathyroidism

Hypoparathyroidism simply describes a PTH level that is too low. Hyperparathyroidism describes a PTH that is too high.

Even though they both have "—thyroidism" in their name, they have nothing to do with hypothyroidism or hyperthyroidism. Those refer to levels of thyroid hormone produced by the thyroid gland, a nearby gland with a totally different function.

Hyperparathyroidism

Hyperparathyroidism can arise because there is some sort of problem with the parathyroid glands. It can also happen when there is a low level of calcium in the blood that the body is trying to correct. For example, some medical conditions that might cause hyperparathyroidism include:

  • Adenoma of the parathyroid glands
  • Hyperplasia of the parathyroid glands
  • Kidney failure
  • Diseases causing poor absorption in the small intestine
  • Vitamin D deficiency
  • Cancer of the parathyroid glands (rare)

Hypoparathyroidism

Hypoparathyroidism occurs less often than hyperparathyroidism. The most common cause results from damage to the parathyroid gland, for example, from damage during surgery or radiation therapy. This might be temporary or permanent. Other potential causes include:

  • Certain autoimmune disorders
  • Low levels of magnesium
  • Certain rare genetic conditions

Tests Often Done With a PTH Test

The physiology of calcium in the body is quite complicated, and it involves several other substances. To properly interpret a PTH test, a medical professional typically needs the results from a calcium blood test as well. This is taken from the same blood sample as the PTH. Other tests might be included as well, depending on the circumstances. Some additional possibilities are:

  • Phosphate
  • Albumin
  • Vitamin D
  • Magnesium

All of these other tests give information about the way calcium is being moved through the body. Together with the PTH, they can give a good indication of any potential underlying medical problems.

Risks and Contraindications

There are very few (if any) risks to having a PTH blood test. It is a basic blood test that can be assessed as part of a simple blood draw. Sometimes there is slight bleeding or bruising at the site of the blood draw. Some people experience lightheadedness or dizziness as well.

If you have a medical condition that makes your blood clot less easily, talk to your doctor before scheduling the test. You may also have a greater risk of excessive bleeding if you take certain medications, like warfarin or other blood thinners.

Before the Test

Make sure your healthcare provider knows about all your medications and supplements before you get your test, as some of these may interfere with the test results.

Some medications may increase PTH levels in certain people. These include steroids, anticonvulsant drugs, and lithium.

Also ask your provider about the best time of day to have the test, as PTH levels may fluctuate during the day.

Timing

The blood draw itself should only take a few minutes. To be prepared, it's best that you allow for longer than that, perhaps an hour or so. You may need to wait for a while after you arrive, and you may have paperwork to fill out as well. You may also want a chance to rest for a bit after the blood draw.

Location

The blood draw might be performed at a hospital, at an outpatient center, or at your local doctor’s office.

What to Wear

It is often helpful to wear a shirt with loose sleeves. This makes it easier to for your phlebotomist to be able to access your veins.

Food and Drink

Usually fasting is not required before a PTH test. However, if you are having other tests done at the same time, some of these might. Your doctor can give you specific instructions if needed.

Cost and Health Insurance

Usually, a PTH test is a relatively inexpensive test that is covered by insurance.

What to Bring

Bring your insurance card. Also, bring a list of the medications you are currently taking.

During the Test

Pre-Test

You’ll probably need to give your information to a receptionist. In some cases, you may have a medical or insurance form to fill out. When they are ready for you, you will be taken to where someone will take your blood sample. This will usually be done by a nurse or a phlebotomist, a health professional trained in drawing blood samples.

Throughout the Test

To perform the PHT test, a healthcare professional needs to take a blood sample. Someone will clean the area. Next, a tourniquet will be applied above the area of the vein to be used, usually the upper arm. You may be asked to squeeze your fist while your phlebotomist finds a good vein to use. The needle will be inserted into a vein in your arm. This usually only hurts for a moment or two. The whole process only takes a few minutes.

After the Test

In almost all cases, you will be able to return to your normal activities right away. If you are dizzy after the blood draw, you may need to sit for a while or have something to eat or drink before going about the rest of your day. Don’t leave the area until you are feeling completely steady on your feet.

Keep the bandage on the site for at least an hour. If it starts to bleed again, apply pressure and raise the site above your head until it stops. It is a good idea to make sure you get enough to drink for the rest of the day. You may also need to avoid heavy activities for a few hours. The sample is promptly sent to a medical laboratory for analysis.

Interpreting Results

Results are often available within a day or two. An average parathyroid hormone level is between 10 and 65 picograms per milliliter (pg/ml), but different versions of the test may have different values. Your test may also indicate whether your PTH is high, normal, or low.

Your results will probably be reported along with your calcium levels, and in some cases, other substances. This will help your healthcare provider get an idea of potential underlying causes.

Follow-Up

Following up after a PTH test will depend on the results of your test. If both your PTH and calcium are normal, probably no follow-up will be needed.

If either is abnormal, you are likely to need follow-up studies. These can help identify any underlying problems. For example, if your PTH is high, but your calcium is low, that means that your parathyroid gland is working normally to try and raise your calcium levels. 

Your physician may need to run other tests (like vitamin D, phosphorus, and magnesium) to see why your calcium is still low.

As another example, if your calcium and PTH were both high, that would mean that the parathyroid gland was producing too much PTH. This might happen, for example, from an adenoma of the parathyroid gland. You might need imaging studies of your neck, so your doctor could examine the gland in more detail. Usually, the first test would be an ultrasound of the area. If necessary, you might need treatment to remove the gland.

If your calcium and your PTH were both low, your doctor would need to try and find out why. For example, certain autoimmune conditions might cause this. You might need to have follow up blood tests to try and figure this out.

If your calcium was high but your PTH was low, this would also probably require follow-up blood tests. These would help figure out the underlying reason your calcium was too high.

Depending on the circumstances, you may need to have a repeat test done. For example, if your PTH is abnormal, you might need to have it repeated after you’ve had your treatment. That can help make sure that the treatment is working for you. You also might need repeat tests if you have a chronic condition that puts you at risk of calcium problems, like severe kidney disease.

Your doctor is the best person to put your results in perspective. Don’t hesitate to ask any questions that you have about what the test means and the best follow-up steps.

A Word From Verywell

It can be uncomfortable waiting for the results of medical tests. This may especially be the case if you or your loved one is suffering a medical problem that hasn’t yet been diagnosed. A parathyroid test is a relatively quick and simple test that can give some additional clues, but most of the time, your health care professional will still need to learn more.

Try to be patient with the diagnostic process, which may take time. Remember that, most of the time, an abnormal parathyroid test arises from a treatable problem. Your medical team will try to keep you informed and involved with every stage of your diagnosis and treatment. 

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