Whether it’s because your doctor orders a routine test to screen for thyroid problems or you’ve been experiencing fatigue, fog, weight gain, and other symptoms of a thyroid disorder, there are nuances to thyroid testing that you’ll want to know about. “There’s a lot of misinformation out there about the tests — it’s important to understand why you’re doing them,” says Laura Ryan, MD, an associate clinical professor within the division of endocrinology, diabetes, and metabolism at The Ohio State University Wexner Medical Center in Columbus.
The Test: TSH
First, your physician will order a blood test to measure your level of thyroid stimulating hormone (TSH), which is an indirect measure of thyroid function. It’s a simple blood test that doesn’t require you to fast, and the results are usually available in 24 hours.
TSH is produced by the pituitary gland, and it stimulates the thyroid to make the hormone thyroxine, which is commonly known as T4. Then the body converts T4 to triiodothyronine (T3), the active form of thyroid hormone that exerts its many effects throughout the body. A high TSH level suggests that the thyroid gland isn’t making enough thyroid hormone, meaning you have hypothyroidism. If your TSH level is low, on the other hand, this usually means the thyroid gland is making too much thyroid hormone — as is the case with hyperthyroidism.
The Test: T3 and T4
If your TSH test comes back abnormal, or it’s normal but you have symptoms that are suspicious of thyroid disorder, your T4 level will be measures, says Christian Nasr, MD, medical director of the Thyroid Center at the Endocrine and Metabolism Institute at The Cleveland Clinic. Depending on the results of the TSH and/or T4 tests, your doctor will make a diagnosis and decide what to do next.
Most mainstream doctors don’t test T3 levels, but according to Ayla Baker, MD, a clinical endocrinologist with Northwestern Medicine in the greater Chicago area, “It can be useful as part of a panel [of tests] to see what the thyroid is doing.” Some doctors will test “Free T3” and “Free T4” levels to measure the hormones floating free in the blood.
The Test: Reverse T3
Reverse T3 is an inactive form of thyroid hormone, and while many conventional doctors don’t measure it, Aviva Romm, MD, author of The Adrenal Thyroid Revolution ($17.99, Amazon), says she finds the test useful for her patients who TSH levels are normal but are still having symptoms of a thyroid problem.
The Test: Antibodies
“Checking thyroid antibodies is fraught with misunderstanding about its utility,” notes Dr. Ryan. Tests for these antibodies (including thyroid peroxidase, thyroglobulin, and TSH receptor antibodies) are usually performed if the doctor suspects the presence of an autoimmune disorder such as Hashimoto’s or Graves’ disease, both of which occur when the immune system attacks the thyroid gland and causes it to make more or less thyroid hormones than the body actually needs.
But Dr. Ryan notes that she will sometimes order these tests if a woman’s TSH level is borderline abnormal and she has a strong family history of a thyroid disorder or an autoimmune disease. In that case, Dr. Ryan explains, the results “can give a hint of whether she’s likely to develop one.”
If the results of any tests your doctor orders are inconclusive, she may advise repeat testing four to six weeks later, by which point your levels may have returned to normal. If they haven’t, treatment may be in order. But as Dr. Nasr says, “There’s some controversy about when to treat.” Indeed, there’s a gray zone when it comes to thyroid function. A subclinical problem can occur if your results are just outside the range of normal, but it can be a warning sign that a full-blown thyroid disorder may be in the woman’s future. “Subclinical hypothyroidism is much more common than full-on hypothyroidism,” says Dr. Ryan. If your results indicate a subclinical problem, your doctor will help you determine next steps.
This article originally appeared in our print magazine, Heal Your Thyroid.