![]() ![]() Follow this link to see our leaflet: Your Guide to Pregnancy and Fertility in Thyroid Disorders. In pregnancy the serum TSH reference range is different from the general population and should ideally be based on reference ranges derived from healthy pregnant women in the same population. These ranges are only a guide and will vary according to laboratory. Typical reference ranges for healthy adults are: Test Laboratories use reference ranges to compare blood test results with results in the normal healthy population. Usually the ‘free’ or active portion of T4 and T3 is measured (i.e., FT4 and FT3). If the TSH level is below the reference range, the blood T4 and T3 will be measured.Ī blood sample is taken from a vein in the arm and sent off to the laboratory for analysis.If the TSH level is above the reference range, the blood T4 will be measured.Many laboratories use a ‘cascade’ system, so the other hormones will be measured if the TSH is not normal. It is good practice for doctors to measure the T4 in addition to the TSH in children, as T4 is essential to brain development. The exception to this is when a pituitary problem is suspected, in which case T4 should be measured as well. In most cases, your TSH level will be the first hormone to be measured, because if this is normal, it is very likely that your thyroid is functioning normally. The usual blood tests done for thyroid function are TSH, T4 and sometimes T3. When the thyroid hormone levels rise above normal, the ‘thermostat’ senses this and the pituitary stops secreting TSH so that the thyroid makes less T4. If the level drops just a little below normal the pituitary reacts by secreting a hormone called thyroid-stimulating hormone (TSH), which activates the thyroid gland to produce more T4. The pituitary senses the level of thyroid hormones in your bloodstream, just as the thermostat in your living room senses the temperature. The amount of T4 and T3 secreted by your thyroid gland is regulated by the pituitary gland, which lies underneath your brain. It is the T3 that is biologically active and regulates your body’s metabolism. This in turn is converted to tri-iodothyronine (T3), which contains three atoms of iodine. One of these is thyroxine, which contains four atoms of iodine and is often called T4. The thyroid secretes two main hormones into the bloodstream. It is made up of two lobes, on either side of your windpipe, joined by a small bridge of thyroid tissue called the isthmus. The thyroid gland lies in the front of your neck just below your Adam’s apple. Contact us Become a member Renew membership Please donate Search SearchĪlso available in Arabic, Polish and Urdu and Mandarin What is the thyroid gland and how does it work? ![]()
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