Interpretation of Your Thyroid Function Tests
Your thyroid function tests show normal thyroid function—no treatment or further testing is needed. 1
Understanding Your Results
Your test results indicate euthyroidism (normal thyroid function):
- TSH 2.35 mIU/L falls well within the normal reference range of 0.45-4.5 mIU/L, with a geometric mean of 1.4 mIU/L in healthy populations 1
- Total T4 12.6 (assuming units of µg/dL or similar) is within normal limits 1
- Free Thyroxine Index (FTI) 2.3 is calculated from total T4 and T3 uptake, and this value is normal 2
TSH is the single most sensitive and accurate test for detecting thyroid dysfunction, with sensitivity above 98% and specificity greater than 92%. 1, 3 Your normal TSH definitively excludes both hypothyroidism and hyperthyroidism. 1
Why TSH is the Gold Standard
The superiority of TSH over other thyroid tests is well-established:
- TSH changes by 466% when comparing euthyroid to subclinical hypothyroid states, while T4 changes by only 20% 3
- The overlap between normal and abnormal thyroid function is only 9% for TSH compared to 92.6% for T4 3
- TSH has an area under the curve of 0.999 for detecting thyroid dysfunction, compared to 0.853 for T4 3
What About the T3 Uptake Test?
The T3 uptake test (also called T3 resin uptake) is an older test that measures thyroid hormone binding proteins, not actual T3 levels. 2, 4 When combined with total T4, it calculates the Free Thyroxine Index (FTI) to estimate free T4 levels. 2 However, this test is largely obsolete and has been replaced by direct free T4 measurement in modern practice. 2, 5
When to Recheck Thyroid Function
With your completely normal results, you do not need routine thyroid screening. 1 Recheck thyroid function only if you develop:
- Unexplained fatigue, weight changes, or temperature intolerance 1
- Hair loss, constipation, or menstrual irregularities 1
- Palpitations, tremor, or anxiety 1
- New cardiac symptoms or arrhythmias 1
Critical Pitfalls to Avoid
- Never treat based on symptoms alone when TSH is normal—thyroid symptoms are extremely non-specific and prevalent in the general population 2
- Avoid unnecessary repeat testing—TSH naturally varies due to pulsatile secretion, time of day, and physiological factors, but values within the normal range do not indicate disease 1, 5
- Do not request additional thyroid tests (free T4, T3, antibodies) when TSH is normal and you have no symptoms—this only leads to confusion and potential overtreatment 2, 6