![]() ![]() *FDH = familial dysalbuminaemic hyperthyroxinaemia Best Pract Res Clin Endocrinol Metab 2013 27:745-62. Pitfalls in the measurement and interpretation of thyroid function tests. Olympia Koulouri, Carla Moran, David Halsall, Krishna Chatterjee, Mark Gurnell. These are discussed in an excellent review by the Cambridge Thyroid Group which run the national reference laboratory for “weird” thyroid function tests: However in some cases the results do not present this anticipated pattern. The table below highlights the common patterns: If TSH levels are high one would expect to see low levels of T3 and T4 If TSH levels are low one would expect to see high levels of T3 and T4. Typical results for free T4 and free T3 are as follows: In most cases now it is the free T4 and T3 levels that are measured. If it is referred to as “bound” it means it is attached to a protein. In response to TSH your thyroid gland will make two forms of T3 and T4. People with Addison’s disease, Turner Syndrome or Down’s syndrome should also be tested regularly as should those with other autoimmune diseases Left untreated this can cause health problems for both yourself and the baby. It is important for your TSH levels to be checked both before deciding to become pregnant AND during the pregnancy as both hyperthyroidism and hypothyroidism can occur at this time. Examples of suggested reference ranges and the normal, low and high TSH levels are shown below : TSH levels have been standardised internationally and vary according to your age and gender. As your levels of T4 and T3 rise the serum TSH falls. As your levels of thyroid hormone (T4 and T3) fall, the serum TSH rises. ![]() ![]() Hypothyroidism will be suspected if the TSH level is high and Hyperthyroidism will be suspected if your TSH level is low due to negative feedback. The pituitary gland is very sensitive and acts as a regulator telling your thyroid gland to increase or decrease T4 and T3 production according their levels in the bloodstream. The doctor will diagnose your condition with the aid of a test looking at your Thyroid Stimulating Hormone (TSH) which is a hormone produced by the pituitary gland in response to your thyroid hormone production. You’ve gone because you think you might have hyperthyroidism because you have some of the symptoms listed on this patient information sheet Whether you wonder if you have hypothyroidism because you have gone to the doctor with symptoms listed in this blog post When a GP suggests a thyroid function test they are looking at the thyroid hormone levels in your bloodstream and comparing them to reference ranges (or levels) in 95% of the healthy population. Blood tests are currently the most accurate way in which to diagnose and manage thyroid disorders. ![]()
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