Why Thyroid Tests Don't Always Work

When symptoms like persistent fatigue, unexplained weight gain, dry skin, brain fog and anxiety are reported to doctors, they may call for a test to see whether an underactive thyroid is to blame. Unfortunately, the test may not reflect a legitimate problem with your thyroid and can be wrong for not just one reason, but several.

The test that is typically done to detect thyroid problems is the TSH test, which detects levels of Thyroid Stimulating Hormone in the blood. TSH levels rise when the pituitary gland senses that hormone T3 and/or T4 levels — the hormones made by the thyroid gland — are lower than they should be in order to regulate body systems.

High TSH levels as measured in the test indicate that the thyroid isn’t functioning the way it should and indicate the need for medication — usually synthroid — to get the thyroid functioning normally again.

The old standard of needing thyroid medication is a TSH level of 5 or higher, but experts now say that lower levels of TSH may still indicate the need for medication. The American Association of Endocrinology says TSH levels of 4.1 or higher should be treated, and the National Academy of Clinical Biochemistry recommends treatment for those at a level of 2.5 or higher, according to HuffPost.

Many doctors are beginning to realize that what constitutes an underactive thyroid may vary from person to person and that the TSH test may not tell the whole story about a thyroid’s functioning. A condition called thyroid hormone resistance can occur in which thyroid hormones test normally in the blood but are low in the tissues where it is needed, like the brain or digestive tract.

Additionally, TSH levels don’t rise in all patients with underactive thyroids. Testing levels of free T3 and T4 can give more accurate levels and reveal thyroid problems that the TSH test won’t catch. Another test called the TRH test can measure the thyroid’s ability to function when stimulated and can be more accurate than the TSH test.

Although many doctors continue to rely on the TSH test, it isn’t the most accurate way to tell if thyroid problems exist, according to Medical Xpress. Being tested more specifically to see if your body is responding to thyroid stimulation or whether your T3 and T4 levels are in the normal range can be a far more accurate indicator of your thyroid’s functioning and can help you get needed treatment even if your function appears to be normal.

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