PTH: Ask Us | Parathyroid Hormone

At a Glance

Why Get Tested?

To determine the cause of calcium imbalances; to evaluate parathyroid function; to diagnose and differentiate between primary, secondary and tertiary hyperparathyroidism; to diagnose hypoparathyroidism; during surgery for hyperparathyroidism, to confirm removal of the gland(s) causing the problem

When to Get Tested?

When calcium blood levels are higher or lower than normal; when you are having surgery for hyperparathyroidism; when your doctor wants to determine how well your parathyroid glands are functioning

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

Since PTH levels vary during the day, samples are usually collected about 8 a.m. Talk to your doctor about sample timing. Current practices do not require fasting.

The Test Sample

What is being tested?

This test measures the amount of parathyroid hormone (PTH) in the blood. PTH helps the body maintain stable levels of calcium in the blood. It is part of a feedback loop that includes calcium, PTH, vitamin D, and, to some extent, phosphorus (phosphate) and magnesium. Conditions and diseases that disrupt this feedback loop can cause inappropriate elevations or decreases in calcium and PTH levels and lead to symptoms of hypercalcemia or hypocalcemia.

PTH is produced by four button-sized parathyroid glands that are located in the neck behind the thyroid gland. Normally, these glands secrete PTH into the bloodstream in response to low blood calcium levels. Parathyroid hormone then works in three ways to help raise blood calcium levels back to normal:

Takes calcium from the body's bone
Stimulates the activation of vitamin D in the kidney, which in turn increases the absorption of calcium from the intestines
Suppresses the excretion of calcium in the urine while encouraging excretion of phosphorus

As calcium levels begin to increase in the blood, PTH normally decreases.

Parathyroid hormone itself is composed of 84 amino acids (sometimes called PTH (1-84)). Once it is released from the parathyroid gland into the blood stream, it has a very short life-span; levels fall by half in less than 5 minutes. The fall is caused primarily by the breakdown of PTH to smaller fragments, mainly PTH (35-84) and PTH (7-84). Although it was originally thought that these fragments are inactive, they are, in fact, active but have different actions than PTH (1-84). These fragments, especially PTH (7-84), appear to do the opposite of PTH, lowering serum calcium and preventing removal of calcium from the bone.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

Since PTH levels vary during the day, samples are usually collected about 8 a.m. Talk to your doctor about sample timing. Current practices do not require fasting.

The Test

How is it used?

An intact PTH is the most frequently ordered parathyroid hormone test. It is ordered to help diagnose the reason for a low or high calcium level and to help distinguish between parathyroid-related and non-parathyroid-related causes. It may also be ordered to monitor the effectiveness of treatment when a patient has a parathyroid-related condition. A calcium test is almost always ordered along with a PTH test. It is not just the levels in the blood that are important, but the balance between them and the response of the parathyroid glands to changing levels of calcium. Usually doctors are concerned about either severe imbalances in calcium regulation that may require medical intervention or in persistent imbalances that indicate an underlying problem.

PTH levels can be used to monitor people who have conditions or diseases that cause chronic calcium imbalances or to monitor those who have had surgery or other treatment for parathyroid tumors.

^ Back to top

When is it ordered?

A PTH test may be ordered when a test for calcium is abnormal. It may be ordered when someone has symptoms associated with hypercalcemia, such as:

Fatigue
Nausea
Abdominal pain
Thirst

PTH may also be ordered when a person has symptoms associated with hypocalcemia, such as:

Abdominal pain
Muscle cramps
Tingling fingers

A doctor may order a PTH, along with calcium, at intervals when someone has been treated for diseases or conditions that affect calcium regulation, such as the removal of a parathyroid tumor, or when a person has a chronic condition such as kidney disease.

Sometimes, an intraoperative PTH test will be ordered when someone who has hyperparathyroidism is undergoing surgery to have abnormal parathyroid tissue removed.

^ Back to top

What does the test result mean?

A doctor will evaluate both calcium and PTH results together to determine whether the levels are appropriate and are in balance as they should be. If both PTH and calcium levels are normal, then it is likely that the body's calcium regulation system is functioning properly.

Low levels of PTH may be due to conditions causing hypercalcemia or to an abnormality in PTH production causing hypoparathyroidism. Excess PTH secretion may be due to hyperparathyroidism, which is most frequently caused by a benign parathyroid tumor.

The table below summarizes results that may be seen:

Calcium - PTH Relationship

If calcium levels are low and PTH levels high, then the parathyroid glands are responding as they should and producing appropriate amounts of PTH. Depending on the degree of hypocalcemia, a doctor may investigate a low calcium level further by measuring vitamin D, phosphorus, and magnesium levels.
If calcium levels are low and PTH levels are normal or low, then PTH is not responding and the person tested probably has hypoparathyroidism. Hypoparathyroidism is a failure of the parathyroid glands to produce sufficient PTH. It may be due to a variety of conditions and may be persistent, progressive, or transient. Causes include an autoimmune disorder, parathyroid damage or removal during surgery, a genetic condition, and severe illnesses. Those affected will generally have low PTH levels, low calcium levels, and high phosphorus levels.
If calcium levels are high and PTH levels are high, then the parathyroid glands are producing inappropriate amounts of PTH. The doctor may order x-rays or other imaging studies to help determine the cause and evaluate the severity of hyperparathyroidism. Hyperparathyroidism is a group of conditions characterized by an overproduction of PTH by the parathyroid glands. It is separated into primary, secondary, and tertiary hyperparathyroidism. Primary hyperparathyroidism is most frequently due to a parathyroid tumor (usually benign) that secretes PTH without feedback control. This puts PTH constantly in the "ON" position, where it can cause hypercalcemia and can lead to kidney stones, calcium deposits in organs, and decalcification of bone. With primary hyperparathyroidism, people will generally have high calcium and high PTH levels, while phosphorus levels are often low.
Secondary hyperparathyroidism is usually due to kidney failure. In people with kidney disease and/or failure, phosphorus may not be excreted efficiently, disrupting its balance with calcium. Kidney disease may also make those affected unable to produce the active form of vitamin D, and this in turn means that they are unable to absorb calcium properly from the diet. As phosphorus levels build up and calcium levels fall, PTH is secreted. Secondary hyperparathyroidism can also be caused by any other condition that causes low calcium, such as malabsorption of calcium due to intestinal disease and vitamin D deficiency. In secondary hyperparathyroidism, people will generally have high PTH levels and low or normal calcium levels.

Sometimes, people with chronic secondary hyperparathyroidism develop high serum calcium and still have high PTH; this is sometimes called tertiary hyperparathyroidism.
If calcium levels are high and PTH levels are low, then the parathyroid glands are responding properly, but the doctor is likely to perform further investigations to check for non-parathyroid-related reasons for the elevated calcium.

^ Back to top

Is there anything else I should know?

Because there are many fragments of PTH, tests for PTH may measure one or more of the fragments. None of the assays for intact PTH measure PTH (35-84), which is actually the fragment of PTH present in highest amounts in blood. Many intact PTH assays measure PTH (7-84) as well. In most people, this fragment is present in much lower amounts than PTH (1-84), so this is not a concern. In kidney failure, a common setting for measuring PTH levels, PTH (7-84) levels increase compared to PTH (1-84), and sometimes over half of what is measured as PTH represents this N-terminal truncated fragment. Some intact PTH assays do not measure this fragment and will give lower PTH results when increased PTH (7-84) is present.

PTH levels will vary during the day, peaking at about 2 a.m. Specimens are usually drawn about 8 a.m.

Drugs that may increase PTH levels include phosphates, anticonvulsants, steroids, isoniazid, lithium, and rifampin.

^ Back to top

Common Questions

1. Can I have an abnormal PTH level without having symptoms?

Yes, if your calcium level changes slowly, you may not have any noticeable symptoms. In this case, the imbalance will most likely be detected by finding an abnormal calcium level during a regular health check, then checking your PTH level.

^ Back to top

2. What does vitamin D have to do with PTH?

If you do not have enough vitamin D, your body will not be able to absorb calcium properly. Vitamin D regulates the intestinal absorption of calcium, while PTH regulates the activation of vitamin D. Too much and too little vitamin D can imbalance calcium metabolism.

^ Back to top

3. What is intraoperative PTH and why is it done?

An "intraoperative PTH" is a PTH test done on a person while they are undergoing parathyroid hormone surgery. When someone has hyperparathyroidism, the usual treatment is surgery to remove the enlarged gland or glands. About 85-90% of the time in primary hyperparathyroidism, only one abnormal parathyroid gland is present, but in the remaining cases two or more of the glands are abnormal. In secondary hyperparathyroidism, usually all four of the parathyroid glands are affected. During surgery, it is important for the surgeon to make sure that he has removed all of the abnormal glands. If all are abnormal, typically three glands are completely removed along with part of the fourth, leaving behind just enough parathyroid tissue to prevent hypoparathyroidism. One way to be sure that all of the abnormal tissue has been removed is to measure PTH before and after an apparently abnormal gland has been removed. If all the abnormal tissue is gone, PTH levels will fall by over 50% within 10 minutes. To be useful, this requires that the laboratory be able to provide the results quickly. This is often called rapid or intraoperative PTH measurement.

^ Back to top

Related Pages

On This Site

Conditions: Kidney Disease

Elsewhere On The Web

FamilyDoctor.org: Hyperparathyroidism
National Endocrine and Metabolic Diseases Information Service: Hyperparathyroidism
National Institute of Child Health and Human Development: What is hypoparathyroidism?
National Cancer Institute, cancer.gov: Parathyroid Cancer
MedlinePlus Medical Encyclopedia: Parathyroid disorders

» See all Article Sources

Article Sources

« Return to Related Pages

NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

Eckman, A (Updated 2009 October 14). PTH. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003690.htm. Accessed May 2010.

Mayo Clinic Staff (2010 May 12). Hyperparathyroidism. MayoClinic.com [On-line information]. Available online at http://www.mayoclinic.com/print/hyperparathyroidism/DS00396/DSECTION=all&METHOD=print through http://www.mayoclinic.com. Accessed May 2010.

Gonzalez-Campoy, J.M. (Updated 2009 July 17). Hypoparathyroidism. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/122207-overview through http://emedicine.medscape.com. Accessed May 2010.

Kim, L. and Makdissi, A. (Updated 2009 September 24). Hyperparathyroidism. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/127351-overview http://emedicine.medscape.com. Accessed May 2010.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

Spengler, R. (2001 April 3, Updated). Parathyroid Hormone. LaurusHealth.com, Medical Tests [On-line information]. Available online at http://www.laurushealth.com/library/healthguide/MedicalTests/topic.asp?HWID=hw8101 through http://www.laurushealth.com.

(2002 march 3, Updated). PTH. Yahoo Health Encyclopedia [On-line information]. Available online at http://health.yahoo.com/health/encyclopedia/003690/0.html through http://health.yahoo.com.

(2001 May 1, Updated). What Does The Parathyroid Do? Jewish Hospital HealthCare Services [On-line information]. Available online at http://jhhs.client.web-health.com/web-health/topics/GeneralHealth/generalhealthsub/generalhealth/endocrine/what_parathyroid.html through http://jhhs.client.web-health.com.

Brown, T., Reviewed (2002 March 3). PTH. Pennhealth.com Health Illustrated Encyclopedia [On-line information]. Available online at http://www.pennhealth.com/ency/article/003690.htm through http://www.pennhealth.com.

(2001 May 13, Updated). Parathyroid Hormone. Colorado State University Hypertextbook, Pathophysiology of the Endocrine System [On-line information]. Available online at http://arbl.cvmbs.colostate.edu/hbooks/pathphys/endocrine/thyroid/pth.html through http://arbl.cvmbs.colostate.edu.

Parathyroid Hormone, Intact Molecule. ARUP's Guide to Clinical Laboratory Testing (CLT) [On-line test information]. Available online at http://www.aruplab.com/guides/clt/tests/clt_p3.htm through http://www.aruplab.com.

Parathyroid hormone test. Hendrick Health System, AccessMed Health Information Library [On-line information]. Available online at http://www.ehendrick.org/healthy/00059880.html through http://www.ehendrick.org.

(2001). Parathyroid Hormone Decreases the Risk of Fractures in Postmenopausal Women with Osteoporosis. John Hopkins arthritis, archived news, 2001 archives [On-line news release]. Available online at http://www.hopkins-arthritis.som.jhmi.edu/news-archive/2001/pth.html through http://www.hopkins-arthritis.som.jhmi.edu.

Brown, T., Updated (2002 March 3, Updated). PTH. MEDLINEplus Health Information, Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003690.htm.

Hyperparathyroidism: What it is and how it's treated. familydoctor.org, from American Academy of Family Physicians [On-line information]. Available online at http://familydoctor.org/handouts/251.html through http://familydoctor.org.

Allerheiligen, D., et. al. (1998 April 15). Hyperparathyroidism. American Family Physician [On-line journal]. Available online at http://www.aafp.org/afp/980415ap/allerhei.html through http://www.aafp.org.

NCI (2002 August 9, Modified). Parathyroid Cancer, Health Professional Version. National Cancer Institute, cancer.gov [On-line information]. Available online at http://www.cancer.gov/cancerinfo/pdq/treatment/parathyroid/HealthProfessional through http://www.cancer.gov.

NCI (2002 August 20, Modified). Parathyroid Cancer, Patient Version. National Cancer Institute, cancer.gov [On-line information]. Available online at http://www.cancer.gov/CancerInfo/doc_pdq.aspx?viewid=426e3a40-31e1-463f-a9ec-7036aa1cc6ab&version=patient through http://www.cancer.gov.

Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC. Winter, w. and Harris, N. Chapter 34: Calcium Biology and Disorders, pp 387-397.

The National Academy of Clinical Biochemistry. Laboratory Medicine Practice Guidelines, Evidence-Based Practice for Point-of-Care Testing Published Guidelines (2007): Intraoperative Parathyroid Hormone; Chp 10, Pp 105-119.

Robert Hurd, MD. PTH. MedlinePlus Medical Encylopedia. Last updated 30 November 2009. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003690.htm. Accessed December 16, 2009.