Total T4 — Normal Range & Interpretation
Full name: Total Thyroxine
Total T4 measures both protein-bound and free thyroxine circulating in serum. Since over 99% of T4 binds to thyroxine-binding globulin (TBG), albumin, and transthyretin, the assay reflects total hormone pool rather than metabolically active hormone. Clinicians order Total T4 alongside TSH and Free T4 to evaluate suspected hypothyroidism, hyperthyroidism, and discordant thyroid panels.
| Male | Female | Unit | Category |
|---|---|---|---|
| 5.0–12.0 | 5.0–12.0 | μg/dL | Thyroid Panel |
Clinical Context
Total T4 measures both protein-bound and free thyroxine circulating in serum. Since over 99% of T4 binds to thyroxine-binding globulin (TBG), albumin, and transthyretin, the assay reflects total hormone pool rather than metabolically active hormone. Clinicians order Total T4 alongside TSH and Free T4 to evaluate suspected hypothyroidism, hyperthyroidism, and discordant thyroid panels.
Elevated Total T4 occurs in Graves disease, toxic multinodular goiter, thyroiditis, exogenous levothyroxine overreplacement, and TBG-increasing states such as pregnancy, oral contraceptive use, estrogen therapy, and acute hepatitis. Depressed Total T4 appears in Hashimoto thyroiditis, central hypothyroidism, severe illness, nephrotic syndrome, malnutrition, and androgen or glucocorticoid therapy that lowers TBG. NPs interpret Total T4 in the context of binding-protein status rather than in isolation.
Classic AANP vignette: pregnancy and estrogen raise TBG and therefore Total T4 without causing true hyperthyroidism, making Free T4 the preferred confirmatory test. Expect questions pairing a pregnant patient with a high Total T4 but normal TSH and Free T4. The boards also test the TSH-first screening approach, levothyroxine dose monitoring, and distinguishing primary from central thyroid disease using paired TSH and T4 results.
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