From the Guidelines
If TSH is elevated, the next test to order is a free T4 (thyroxine) level. This test measures the amount of unbound thyroid hormone in the bloodstream and helps determine if you have primary hypothyroidism 1. When TSH is elevated but free T4 is normal, this indicates subclinical hypothyroidism. If both TSH is high and free T4 is low, this confirms overt primary hypothyroidism.
Some key points to consider when interpreting these results include:
- The combination of TSH and free T4 provides a complete picture of thyroid function and helps clinicians determine if thyroid hormone replacement therapy is necessary and at what dose 1.
- In some cases, testing for thyroid antibodies like thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies (TgAb) may also be appropriate to identify autoimmune thyroid disease such as Hashimoto's thyroiditis, which is the most common cause of hypothyroidism.
- The USPSTF found no direct evidence that treatment of thyroid dysfunction based on risk level alters final health outcomes, but treatment is generally recommended for patients with a TSH level that is high enough to warrant concern 1.
- Follow-up testing of serum T4 levels in persons with persistently abnormal TSH levels can differentiate between subclinical and “overt” thyroid dysfunction 1.
The most recent and highest quality study, from 2015, supports the use of free T4 as the next step in evaluation after an elevated TSH is found 1. This approach prioritizes the assessment of thyroid function and guides treatment decisions to improve patient outcomes in terms of morbidity, mortality, and quality of life.
From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Elevated Thyroid-Stimulating Hormone (TSH) Diagnosis
If Thyroid-Stimulating Hormone (TSH) is elevated, the following tests can be ordered:
- Free thyroxine (FT4) and free triiodothyronine (FT3) measurements to confirm and assess the level of hypo and hyperthyroidism (overt or subclinical) 2
- Anti-thyroid peroxidase antibodies (TPO) to predict the development of hypothyroidism 3
- Thyroxine (T4) and tri-iodothyronine (T3) determinations to assess thyroid function 2
Treatment and Follow-up
For patients with elevated TSH, treatment with levothyroxine (LT4) monotherapy may be considered, especially for those with TSH >10 mIU/L or pregnant women 4, 5
- Follow-up involves regular assessment of TSH levels and symptom relief 5
- Repeat TSH testing after six months for male subjects and participants with baseline TSH equal or less than 6.9 mIU/L 3
Special Considerations
In patients with central hypothyroidism, other pituitary hormones should be evaluated, especially assessment of the hypothalamic-pituitary-adrenal axis 4
- In patients with persistently elevated TSH despite an apparently adequate replacement dose of LT4, poor compliance, malabsorption, and the presence of drug interactions should be checked 4