Does this test have other names?
Parathyroid hormone assay, parathyrin, parathormone, PTH-C-Terminal
What is this test?
This test measures a substance called parathyroid hormone (PTH) in your blood. PTH
is made by four tiny parathyroid glands in your neck. PTH circulates in your blood
and is needed to regulate the level of calcium in your blood. Your heart, bones, nervous
system, and kidneys need a normal calcium level in the blood to work the way they
If your calcium level is too low, your parathyroid glands release PTH to get more
calcium into your blood. If your calcium level is too high, your parathyroid glands
stop producing PTH. Measuring the amount of PTH in your blood helps your healthcare
provider find out the cause of an abnormal calcium level.
This test is usually done early in the morning, the best time best to measure PTH.
Why do I need this test?
You may need this test if an earlier blood test found that your calcium level was
too high or too low. You may also need this test if you have signs or symptoms of
an abnormal calcium level. PTH levels help your healthcare provider find out whether
an abnormal calcium level is from a problem with your parathyroid glands or has another
Signs and symptoms of high calcium, or hypercalcemia, include:
Aches and pains
Symptoms of low calcium, or hypocalcemia, include:
What other tests might I have along with this test?
Your healthcare provider may order other blood tests along with a PTH test. It's common
to have your blood calcium level checked along with the PTH level. Other blood mineral
levels may also be checked. You may also have tests to measure your kidney function.
What do my test results mean?
Many things may affect your lab test results. These include the method each lab uses
to do the test. Even if your test results are different from the normal value, you
may not have a problem. To learn what the results mean for you, talk with your healthcare
Results are given in picograms per milliliter (pg/mL). This test measures three forms
of PTH: intact molecule, N-terminal fragments, and C-terminal fragments. Normal levels
N-terminal: 8 to 24 pg/mL
Intact molecule: 10 to 65 pg/mL
C-terminal: 50 to 330 pg/mL
Some of the more common causes of high PTH levels are:
Overactive parathyroid glands, a condition called hyperparathyroidism; this can have
Failure of the kidneys to respond normally to PTH
Inherited vitamin D deficiency
Spinal cord injury
Low calcium not related to the parathyroid glands
Some of the more common causes of low PTH levels are:
Underactive parathyroid glands, a condition called hypoparathyroidism; this can have
Overactive thyroid gland, or hyperthyroidism
Elevated calcium not related to the parathyroid glands
Your healthcare provider will look at the PTH results along with the blood calcium
level and possibly other tests to better understand what the results mean.
How is this test done?
The test requires a blood sample, which is drawn through a needle from a vein in your
Does this test pose any risks?
Taking a blood sample with a needle carries risks that include bleeding, infection,
bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight
stinging sensation or pain. Afterward, the site may be slightly sore.
What might affect my test results?
Conditions such as higher than normal blood fats, vitamin D deficiency, and milk-alkali
syndrome (Burnett's syndrome) can interfere with your test results. Many types of
medicines can also alter the results. These include medicines with phosphates and
vitamin A or D overdoses.
How do I get ready for this test?
You may need to fast for 10 hours before the test. Be sure your healthcare provider
knows about all medicines, herbs, vitamins, and supplements you are taking. This includes
medicines that don't need a prescription and any illicit drugs you may use.