Thyroid Function Tests

by Carlo Raj, MD

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    What are my key thyroid function tests? The most sensitive is TSH. For example, if you find a patient with Hashimoto and there was decreased levels of T3, T4, what are you going to measure? TSH and you find that to be elevated. What if your patient had secondary hypothyroidism? That means that the anterior pituitary is not functioning properly. Your TSH levels will be decreased, thus T3, T4. The TSH levels allow you to ask if a change in thyroid hormone is being driven by the pituitary. For example, if T4 is low and TSH also low then where’s my underlying issue? Not in the thyroid, it is in your anterior pituitary. Free T4 – directly measures the free hormone. Free T4. Very sensitive, bypasses effects of disease and drugs on thyroid binding globulin levels. Free T4. We’ll talk more about TBG. Thyroid binding globulin would be the binding protein that’s being synthesized and released by the liver, influenced by the hormone estrogen that we’ll talk about later in pregnancy. Total T4. Total. What does total mean to you? It’s a concept. Free plus bound. Free plus bound is total. When you have total, which one of those components makes up majority of your total? Not the free. It’s the bound. Clear? So, total means free and bound. Always keep that in mind. That will make your life so much easier later when we talk about pregnancy. So, total T4 greater than 99% protein bound… What’s the name of that protein? Thyroid binding globulin. Coming from where? From the liver. Influenced by whom? Estrogen. I’ve done that plenty. Need to take into account TBG status and thus, helps in diagnosis of hyperthyroidism, hypothyroidism only under conditions of normal TBG levels. So, you need to make sure that you rule...

    About the Lecture

    The lecture Thyroid Function Tests by Carlo Raj, MD is from the course Thyroid Gland Disorders.

    Included Quiz Questions

    1. TSH
    2. Free T4
    3. Total T4
    4. Thyroglobulin
    5. TRH
    1. Estrogen
    2. Glucocorticoids
    3. Androgens
    4. Malnutrition
    5. Protein-losing states

    Author of lecture Thyroid Function Tests

     Carlo Raj, MD

    Carlo Raj, MD

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