The thyrotropin releasing hormone (TRH) stimulation test is a diagnostic method used to detect hypothyroidism, or an underactive thyroid gland. Three other tests that most practitioners typically order to detect thyroid hormone levels are the thyroid stimulating hormone (TSH) test, the T3 and the T4.
To review the basic endocrinology behind thyroid function, the hypothalamus is the gland in the brain that secretes TRH. In turn, this stimulates the pituitary gland, also located in the brain, to release TSH. Finally, TSH stimulates the thyroid gland to produce thyroid hormones T3 and T4.
Hypothyroidism can present with a variety of symptoms, including feelings of fatigue and weakness, weight gain, intolerance to cold temperatures, forgetfulness and difficulty to think clearly, constipation and dry skin. Women can experience heavy or irregular menstrual periods. Untreated hypothyroidism in pregnant women can have harmful effects on their baby. If hypothyroidism is left untreated, cholesterol levels can elevate, thus increasing risks for a heart attack or stroke. Symptoms do present gradually over time. When symptoms do not subside or worsen, it is time to seek a diagnosis.
Until several years ago, the TRH stimulation test was the screening of choice for determining thyroid function. The THR stimulation test requires the collection of an initial baseline sample of blood, followed by an intravenous injection of a synthetic form of THR to stimulate the pituitary gland to release TSH. Additional blood samples are obtained over a period of time following the injection to track levels of TSH. The TRH stimulation test can be a valuable tool in confirming hypothyroidism in patients who exhibit obvious symptoms of the disorder, yet show borderline results on a TSH test. The TRH stimulation test can also identify secondary hypothyroidism, which results from a disorder of the pituitary gland, as well as tertiary hypothyroidism, which would be indicative of a disorder of the hypothalamus. Early detection of hypothyroidism, which can take years to develop and consistently be revealed on a TSH test, can be achieved with the TRH stimulation test at the onset of symptoms.
Today most physicians opt for the TSH test in lieu of the TRH stimulation test. The manufacturer discontinued production of protirelin, the injectable synthetic TRH used to perform the TRH test, several years ago. Injectable protirelin can be obtained through compounding pharmacies; however, physicians question the quality for use in the TRH stimulation test. The TSH test requires no such injections, only one blood sample is needed, and the test is much simpler to perform and interpret. The difference between the TSH test and the TRH test can be compared to a single photograph versus live film footage, respectively. The TSH is like one snapshot as it measures thyroid levels in one instant of time, the time at which the blood sample was obtained. The TRH stimulation test is more like a whole film segment, illustrating hormone levels over a period of time. Since TSH levels can change constantly due to an array of metabolic influences, a single reading can misrepresent how adequately the thyroid is functioning. The TRH stimulation test provides a more detailed picture.
Fortunately, hypothyroidism is easily treated, usually with prescribed thyroid hormone oral medication. Symptoms begin to abate fairly quickly and patients note marked improvement in their overall physical stamina and emotional outlook. The hypothyroid patient will likely remain on the medication for life and will be required to follow-up periodically with their physician. Thyroid hormone level screenings will also need to be performed regularly as directed by the physician in order to verify that the medication is continuously used at the ideal dosage for maintaining optimal thyroid function.
Early detection through a TRH stimulation test can lead to early intervention, thus relieving the patient with hypothyroidism of symptoms so that he or she can get back to enjoying a more positive quality of life.
Currently, doctors evaluate three blood test to see if your thyroid is low, TSH, T3 and T4. If you have questions regarding the TRH stimulation test, contact Raphael Kellman, M.D. at 212-7-1118
