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What is a Parathyroid Hormone (PTH) test? 

Parathyroid Hormone (PTH) is produced by four parathyroid glands in the neck. It circulates in the blood and plays an essential role in regulating calcium levels in the body. Calcium is necessary for the normal functioning of kidneys, heart, nervous system and bones.

When calcium levels reduce in body, parathyroid glands release PTH to stabilise them and n case of high calcium levels, PTH production is stopped. Thus, measuring PTH levels helps determine the cause of abnormal calcium levels in the body.

The alternate terms for this test are parathormone (PTH), intact PTH, PTH intact molecule, hypoparathyroidism - PTH blood test and hyperparathyroidism - PTH blood test.

  1. Why is a PTH test performed?
  2. How do you prepare for a PTH test?
  3. How is a PTH test performed?
  4. What do PTH test results indicate?

A PTH test is recommended to individuals who get abnormal (high or low) calcium levels results in another blood test. This test is also performed if patients present with signs and symptoms of abnormal calcium levels.

Estimating PTH levels helps doctors to determine the cause of abnormal calcium levels in the body. Following are the signs and symptoms of low calcium levels (hypocalcaemia):

 Following are the signs and symptoms of hypercalcaemia:

The test is also conducted when low phosphorus levels, severe osteoporosis or kidney disease is observed.

PTH levels increase during sleep hours and reduce during mid-morning and late afternoon time. Hence, you should ask your healthcare provider if fasting is needed before the test. The levels might also fluctuate due to seasonal changes. Blood sample for this test is usually withdrawn during the late afternoon and mid-morning hours. Make sure to inform your doctor about the timing of the sample withdrawn

For a PTH test, a blood sample will be collected from a vein in your hand.

The likely risks associated with this blood test include bleeding, light-headedness, bruising and infection. However, most of these symptoms subside on their own. If you notice persistent discomfort, check in with a doctor as soon as possible.

The normal results vary among different laboratories as they depend on the measurements and test specimens used. Consult your doctor for the interpretation of results.

Normal results: Normal PTH levels range from 10 to 55 picograms per millilitre (pg/mL).

Abnormal results: Lower than normal PTH levels might indicate the following:

  • Autoimmune destruction of the parathyroid gland
  • Tuberculosis and sarcoidosis
  • Low magnesium levels in the blood
  • Excess vitamin D intake
  • Accidental removal of the parathyroid gland during thyroid surgery
  • The inability of the parathyroid glands to produce PTH
  • Cancers that started in other body parts, such as the colon, breast and lungs, which have spread to the bone
  • Effect of radiation on the parathyroid glands
  • Excess sodium bicarbonate, certain antacids and calcium supplements

Higher than normal PTH levels might indicate the following:

  • Pseudohypoparathyroidism (inability of the body to produce a response to PTH)
  • Inadequate calcium absorption from the gut, insufficient calcium intake or loss of calcium through urine
  • Swelling in the parathyroid glands
  • Breastfeeding or pregnancy (rare cases)
  • Disorders that increase phosphorous or phosphate levels in the blood, such as chronic kidney disease
  • Adenomas (tumours in the parathyroid gland)
  • Vitamin D disorders due to lack of sun exposure, problems in absorption, use or breakdown vitamin D in the body

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.  

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References

  1. University of Rochester Medical Center. Parathyroid Hormone. Rochester, New York [internet].
  2. Penn State Health. Parathyroid hormone (PTH) blood test. Milton S. Hershey Medical Center; Pennsylvania
  3. Carl A. Burtis, David E. Bruns. Tietz Fundamentals of Clinical Chemistry and Molecular Diagnostics - E-Book. Elsevier Health Sciences, 2014
  4. American Association for Clinical Chemistry. Contemporary Practice in Clinical Chemistry. Washington, D.C, United States
  5. Richard A. McPherson, Matthew R. Pincus. Henry's Clinical Diagnosis and Management by Laboratory Methods E-Book. Elsevier Health Sciences, 2017. [internet].