Thyroid conditions such as hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid) are more common in people with Down syndrome. Current guidelines for adults with Down syndrome recommend checking for thyroid conditions with a blood test every 1-2 years.
Our thyroid glands make multiple thyroid hormones. As a result, there are several different blood tests that can be done. The different blood tests check for the level or amount of the different thyroid hormones in our blood. The three most common labs measured to assess thyroid function are TSH (thyroid stimulating hormone), Free T4 (thyroxine), and Free T3 (triiodothyronine).
TSH is made in the brain and signals the thyroid gland to make T4 and T3. T4 and T3 are the hormones that go to the other tissues and organs of the body to "do the work of the thyroid."
Assessment of symptoms, physical findings, and review of lab values are all part of assessing for thyroid conditions. For lab values:
A high TSH and a low T4 are consistent with hypothyroidism.
A low TSH and a high T4 (and/or T3) are consistent with hyperthyroidism.
A high TSH with a normal T4 are consistent with subclinical hypothyroidism (it is called subclinical hypothyroidism because only the TSH value is abnormal and T3 and T4 levels are normal).
Thyroid function impacts many functions in our body. Therefore, if the thyroid function is abnormal (high or low), many body functions may be altered. The body functions include heart rate, bowel function, cognition (ability to think), skin texture, ability to lose weight, and more.
It is generally accepted that the values for normal thyroid function are the same for people with and without Down syndrome. There has been some discussion that normal values should be defined differently for people with Down syndrome. However, consensus has not been reached on this question.
The TSH test is typically the first (and only) blood test that is done. A study done in people without Down syndrome that was published online in June 2020 questions this approach of primarily testing for TSH. The study was a meta-analysis or a review of a selection of previously published studies. It concluded that measuring another thyroid hormone - Free T4 - may provide the most helpful information. As noted above, many body functions can be affected by thyroid function. The status of those body functions will vary if thyroid function is normal, high, or low. The study found that Free T4 may more accurately reflect the health conditions and symptoms that the thyroid can affect. Of the three tests, when the T4 was abnormal, the functions were more likely to be abnormal; when the T4 was normal, the body functions were more likely to be normal. A summary of the journal article is available from Medscape (requires registering for a free account to review the article).
A couple points to note:
The studies that were reviewed in the meta-analysis were not done with people with Down syndrome. We do not know if the findings would be different for people with Down syndrome.
Measuring TSH has long been the standard, and a change will require further analysis. This is one study. Further research is needed, as physicians in the summary article linked above note.
At the Adult Down Syndrome Center, we recommend thyroid blood testing as part of regular screening (every 1-2 years). We also check thyroid blood tests when an individual has symptoms of thyroid dysfunction. We consider checking both TSH and Free T4 (and sometimes T3) depending on the symptoms of the individual. This can provide more insight for making treatment recommendations and decisions.
While this information needs further study, especially in people with Down syndrome, what might this tell us now? Here are some considerations:
If the TSH is normal but the person is still having symptoms of thyroid dysfunction, it might be beneficial to also check the T4.
If the person feels well and the T4 is normal but the TSH is abnormal, it might be reasonable to make no changes with regards to medication but to repeat the labs sooner than would be recommended by the GLOBAL Medical Care Guidelines for Adults with Down Syndrome or the standard follow-up testing if the person is taking thyroid medication.
Each individual is unique. Assessments of labs and symptoms and discussion with your healthcare provider can help optimize thyroid function.
Additional resources on thyroid conditions in people with Down syndrome are available in the Endocrinology section of our Resource Library. For general information about thyroid conditions, please see the Mayo Clinic's resources on hypothyroidism and hyperthyroidism.