Health

Thyroid Index (TSH/FT4/FT3 Interpretation)

Interpret the thyroid axis by pattern-reading TSH with FT4 and (optionally) FT3. Adult reference ranges: TSH 0.4–4.0 mIU/L, FT4 0.8–1.8 ng/dL (≈10–23 pmol/L), FT3 2.3–4.2 pg/mL (≈3.5–6.5 pmol/L). High TSH + low FT4 → overt primary hypothyroidism; high TSH + normal FT4 → subclinical hypothyroidism; low TSH + high FT4/FT3 → overt primary hyperthyroidism; low TSH + normal FT4 → subclinical hyperthyroidism, exogenous hormone, or resolving thyroiditis (check FT3 for T3 toxicosis); low/normal TSH + low FT4 → central hypothyroidism; high TSH + high FT4 → TSH-secreting adenoma or thyroid hormone resistance. Low FT3 with normal TSH/FT4 indicates low-T3 (non-thyroidal illness) syndrome. Units selectable for TSH, FT4, FT3. Derived from ATA 2014/2016, NACB 2002, Garber 2012, and MDCalc. Not medical advice.