Thyroid Panel

Subclinical hypothyroidism: TSH elevated (4.5-10) with normal free T4. Treat if TSH >10, or if TSH 4.5-10 with symptoms, positive TPO antibodies, pregnancy, or infertility. Repeat in 6-8 weeks to confirm persistence. Subclinical hyperthyroidism: TSH low (0.1-0.4) with normal free T4/T3. Often transient. Repeat in 6-8 weeks. Treat if TSH <0.1 (especially age >65 due to AFib risk) or if symptomatic.

Biotin supplements (common in hair/nail vitamins) can falsely elevate free T4 and lower TSH in immunoassays — hold for 48-72 hours before testing. Levothyroxine: draw labs before morning dose. Amiodarone can cause both hypo- and hyperthyroidism. Steroids, dopamine, and severe illness (sick euthyroid) suppress TSH. Pregnancy: TSH normally decreases in first trimester due to hCG. Estrogen (OCPs, HRT) increases TBG, raising total T4 but not free T4.

Check TPO antibodies: subclinical hypothyroidism (predicts progression), goiter evaluation, postpartum thyroiditis, Type 1 diabetes or other autoimmune conditions. Check TSH receptor antibodies (TRAb): suspected Graves disease (distinguishes from toxic multinodular goiter or thyroiditis). Check thyroglobulin antibodies: thyroid cancer monitoring (interfere with thyroglobulin assay). TPO antibodies are positive in ~95% of Hashimoto and ~75% of Graves disease.