The thyroid gland is a small butterfly shaped gland that is located below the larynx in the lower neck region. It is a part of our endocrine system. As is the case with other endocrine glands, the thyroid gland is also responsible for the secretion of certain hormones. These hormones are called thyroxine (T4) and triiodothyronine (T3). T3 and T4 hormones play a vital role in the regulation of metabolism. The secretion of these thyroid hormones is regulated by another hormone called thyroid-stimulating hormone (TSH). This hormone is released by the pituitary gland. If a person is exhibiting thyroid disorder symptoms, certain diagnostic tests are conducted to measure the levels of T3, T4 and TSH in blood. These blood tests are essential for diagnosing any thyroid disorder. The thyroid-stimulating hormone activates the thyroid gland thereby facilitating the secretion of thyroid hormones. This is the reason why the TSH blood test is central to the diagnosis of thyroid gland disorders.
Abnormal TSH levels are indicators of thyroid problems. Since medical science is constantly evolving with time, doctors are now relying on newer tests and parameters for diagnosing medical conditions. For instance, the normal reference range for the TSH test has been reviewed and medical experts are now diagnosing thyroid disorders on the basis of TSH 3rd generation normal range. So what is reference range for the new 3rd generation TSH test and how does it help in the diagnosis of thyroid disorders? Here is some information that will throw some light on this blood test.
TSH Normal Levels
Whenever the levels of T3 and T4 are high, the pituitary gland releases lesser amounts of TSH. On the other hand, the pituitary gland releases TSH in higher amounts if thyroid levels are low. So, a sluggish or an overactive thyroid gland can be diagnosed by checking the TSH levels in blood. Doctors often order the thyroid function tests when a patient exhibits the symptoms of a thyroid disorder. Once the blood sample is taken, the levels of T3, T4 and TSH are measured using specialized diagnostic techniques. Radioimmunoassay (RIA) refers to a sensitive assay technique that was earlier used for checking the concentration of TSH levels in the blood. This technique was used to provide the first generation of clinical assays for the TSH. The first generation provided the functional or analytical sensitivity of about 1.0 mIU/L.
The term 'analytical sensitivity' refers to the lowest concentration of a substance that can be detected in a sample using an analytic method. It is also referred to as the limit of detection. The analytical sensitivity is greater if the assay is able to detect small changes in the concentration. Since normal TSH levels lie within the range of 0.5 to 5.0 mIU/L, with the detection limit of 5 to 10 mIU/L, the first generation clinical assays were not very effective when it came to detecting mild hypothyroidism, wherein the patient's TSH levels were slightly more than 5 mIU/L. When new technologies and techniques such as immuno-radiometric assay (IRMA) became available, the TSH second generation provided improved analytical sensitivity wherein limit of detection was as low as 0.1 mIU/L. With the limit of detection becoming as low as 0.1 mIU/L, the second generation TSH assay proved to be a valuable diagnostic tool for detecting hyperthyroidism.
TSH 3rd Generation Normal Levels
Recently, the TSH normal range has been modified. The 3rd generation TSH assay allows the measurement of thyroid-stimulating hormone at very low concentrations. It is therefore referred to as ultra-sensitive TSH. It is this accuracy that makes it different from the first and second generation TSH tests. According to the American Association of Clinical Endocrinologists, the range for TSH 3rd generation is taken to be anywhere between 0.3 and 3.0 mIU/L, as opposed to the second generation range of 0.5 to 5.0 mIU/L. The functional sensitivities for the third generation TSH assays lies between 0.01 to 0.02 mIU/L. Due to its sensitivity to lower concentration of TSH, the third generation TSH assay is considered to be more accurate. This updated reference range can account for the symptoms experienced by many people. The modification of normal levels of TSH has made a great impact when it comes to the diagnosis of thyroid disorders.
If the TSH level is below 0.3 mIU/L, it is indicative of hyperthyroidism, whereas a reading that is higher than 3.0 mIU/L indicates hypothyroidism. Due to the narrower reference range, there is a better chance of diagnosing people with thyroid disorders. Since the third generation test allows the doctors to check for TSH even at very low concentrations, this test is used to monitor the levels of thyroid-stimulating hormone for those who are taking medicines for controlling thyroid. Certain medicines can interfere with the TSH 3rd generation testing which is why you should tell your doctor about the drugs you might be using. The newer range can now account for the unexplained symptoms that people might have been experiencing. However, this increasingly sensitive TSH test alone cannot help in giving a clear picture of the thyroid gland function. It must be ordered along with the T3, T4 and the Free T3 and Free T4 tests.
The new third generation TSH test has certainly proved to be beneficial in diagnosing thyroid disorders. The levels of thyroid hormones that are reflected in the results of this 3rd generation TSH test along with T3 and T4 tests can be of great assistance when it comes to formulating an accurate diagnosis. Many people who were experiencing symptoms related to thyroid, but were not diagnosed with a thyroid problem as per the old TSH normal range, can now be diagnosed with the help of this third generation test. Once the condition is diagnosed, medicines can be prescribed for keeping the thyroid disorder under control.