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Thyroid
Question | Answer |
---|---|
iodine deficiency leads to lack of thyroid hormone production (Hypothyroidism). | Leads to mental retardation, cretinism in fetus |
T3 is 4-8x more active metabolically than T4. T3 is ‘active’ form of thyroid hormone; T4 ‘pre-’ hormone; thyroglobulin ‘pro’ hormone | Released T4 converted to T3 by liver and kidney |
Three major thyroid hormone binding proteins: 1. Thyroxine-binding globulin (TBG) 2. Thyroxine-binding prealbumin (TBPA; transthyretin) 3. Albumin T4 and T3 levels affected by levels of available binding proteins. | |
Graves’ disease: most common cause of hyperthyroidism; antibody to TSH receptor protein; receptor stimulation leads to thyroid growth; excessive levels of thyroid hormone produced; diagnosed with tests to measure antibodies to TSH receptor. | Lab testing: high free T4 and/or T3 level with undetectable TSH; thyroid stimulating antibodies (TSIs) and TSH receptor antibodies usually positive. |
Chronic lymphocytic thyroiditis (Hashimoto’s thyroiditis): hypothyroidism; antibodies result in decreased thyroid hormone production | Low free T4 level with a normal or high TSH |
TSH Specimen collection and storage: serum or plasma with EDTA or heparin. Specimens stable at 4oC for 24h or -20oC for 1 month. | Reference Intervals (Total T4; nmol/L): Adults: Males and females 59-135nmol/L. |