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THYROID DISORDERSDiagnostic Studies in Thyroid DisordersTestCommentsThyroid-stimulating Most sensitive test to detect 1 hypo- and hyperthyroidismhormone (TSH) May be inappropriately normal in central etiologiesT’d by dopamine, steroids, severe illnessT 3 and T 4 immunoassays Measure total serum concentrations (∴ influenced by TBG)Free T 4 immunoassay Free T 4, not influenced by TBG, increasingly popular(FT 4)Thyroxine-bindingc TBG (∴ c T 4): estrogens, OCP, pregnancy, hepatitis, opioids,globulin (TBG)hereditaryT TBG (∴ T T 4): androgens, glucocorticoids, nephriticsyndrome, cirrhosis, acromegaly, nicotinic acid, hereditaryReverse T 3Inactive, c’d in sick euthyroid syndromeThyroid antibodies Antithyroid peroxidase (TPO) seen in Hashimoto’s (high titer),painless thyroiditis and Graves’ disease (low titer)Thyroid-stimulating Ig (TSI) and thyrotropin-binding inhibitoryimmunoglobulin (TBII) seen in Graves’ diseaseThyroglobulinc’d in goiter, hyperthyroidism and thyroiditisT’d in factitious ingestion of thyroid hormoneTumor marker for thyroid cancer only after totalthyroidectomy and radioiodine therapyRadioactive iodine uptake Useful to differentiate causes of hyperthyroidism(RAIU) scanc uptakehomogeneous Graves’ diseaseheterogeneous multinodular goiter1 focus of uptake w/ suppression of rest of gland hotnoduleno uptake subacute painful or silent thyroiditis,exogenous thyroid hormone, struma ovarii, recent iodineload, or antithyroid drugsTHYROID 7-3Figure 7-1 Approach to thyroid disordersdecreasedTSHnormalincreaseddecreasedFree TnormalCentralincreasedHypothyroidismSubclinicalhyperthyroidism? secondary(central) diseasePrimaryhyperthyroidismRAIUdecreasedPrimaryhypothyroidismFree TnormalSubclinicalhypothyroidismincreasedTSH-secretingadenoma(central hyperthyroidism)orThyroidhormoneresistancediffusefocalnonehomogeneousheterogeneousserum thyroglobulin↓ ↑Graves’diseaseToxicmultinodulargoiterFunctioningadenomaThyrotoxicosisfactitiaThyroiditisStruma ovariior Iodine load