The PTH Blood Test and Diagnosis

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Why the PTH Test May Be Ordered

There are a variety of reasons that the physician may have ordered a PTH blood test. It may be ordered when the patient has unusual calcium values, suffers from kidney disease and when the physician suspects a disorder associated with the parathyroid gland(s). Patients already diagnosed with a condition of the parathyroid may have PTH testing prior to surgery to remove the gland or to monitor the effectiveness of a particular treatment. This test may also be ordered to rule out the parathyroid as a cause to problems associated with vitamin D production and imbalances of phosphate or magnesium.

Testing and Preparation

The PTH test is a blood test that will require a blood sample. The procedure can be performed in a physician’s office, hospital or at another approved clinic. Blood is usually obtained from the arm, via a needle, after the area has been cleansed with alcohol. There are special preparations for this test. The patient must fast at least ten to twelve hours before the test, but the patient might be allowed to drink water. Some medications such as steroids, anticonvulsants and some antidepressants can affect test results. The patient should check with their physician regarding these medications prior to testing. In most cases, the test is performed early in the morning. This is because PTH levels may fluctuate throughout the day, altering results of the test.

Normal PTH Blood Values

PTH values tend to vary between individuals and laboratories. Factors such as age, sex and underlying health conditions must be taken into consideration. However, Med Help establishes general guidelines for these values to be between 10 and 55 picograms per milliliter, also expressed as pg/mL. Ranges that exceed or are below these values are considered abnormal and can be indicative of disease or disorder. Kidney disease, hyperparathyroidism and hypoparathyroidism are a few of the conditions which may be associated with abnormal parathyroid hormone levels. However, abnormal PTH levels can also be associated with absorption problems and disorders unrelated to the parathyroid.

Tests Commonly Associated With the PTH Test

To confirm or eliminate a possible diagnosis, other tests may be ordered along with the PTH blood test. This can include tests for calcium, vitamin D, phosphate and magnesium. Many times these additional tests will be required to differentiate between various disorders and causes. For example, low levels of PTH can signify disorder within the parathyroid but if calcium levels are low as well, the problem is not likely caused by this gland and further testing is needed. Accurate diagnosis relied on these tests in combination with the PTH.


PTH: The Test. Lab Tests Online. Modified 18, June 2010. Viewed 12, July 2010.

PTH: Information, Symptoms, Treatments and Resources. Med Help. 24, October 2007. Viewed 12, July 2010.