T4 level refers to the concentration of thyroxine (T4), a key thyroid hormone produced by the thyroid gland, in the bloodstream. T4 helps regulate metabolism, energy production, and many bodily functions. Laboratory tests may measure total T4, free T4, or both, often alongside thyroid-stimulating hormone (TSH) to evaluate thyroid function. Abnormally low T4 levels suggest hypothyroidism, while elevated T4 levels can indicate hyperthyroidism or over-replacement with thyroid medications. Chronic abnormalities in T4 can contribute to weight changes, cardiovascular issues, fatigue, and other symptoms. For insurers, T4 results, along with TSH and clinical context, provide important insight into the stability and control of thyroid disorders in underwriting.

In underwriting, T4 levels are reviewed when applicants report thyroid disease, use levothyroxine or antithyroid medications, or present with symptoms that may be thyroid-related. Underwriters look for stable, well-controlled T4 and TSH values documented in recent labs and physician notes. Mild, well-managed hypothyroidism often receives favorable consideration, while poorly controlled hyperthyroidism or associated cardiac issues can lead to ratings or postponement. Advisors can improve outcomes by encouraging clients to obtain up-to-date thyroid labs and demonstrate consistent medication adherence. Understanding T4 level helps advisors translate technical lab values into practical expectations about insurability and the importance of thyroid control for overall health.