Need to check your thyroid? Maybe not

By | July 23, 2019

As medical science advances, we have more tests and biomarkers available to help identify illnesses. Yet overdiagnosis and overtreatment that may occur following abnormal results can cause dangerous adverse effects and costly consequences. Hypothyroidism — a lower than normal range of thyroid hormones — may be the poster child for this problem because it is such a common condition.

What is hypothyroidism?

At the front of your neck lies the thyroid, a butterfly-shaped gland that makes the hormone T4. When released into the bloodstream, T4 converts to T3, the most active form of thyroid hormone. Having sufficient levels of these hormones is important because the thyroid regulates body temperature, metabolism, blood pressure, and heart rate.

Hypothyroidism occurs when the thyroid is underactive (not working optimally). It affects as many as five in 100 people. Symptoms of hypothyroidism include fatigue, cold intolerance, constipation, dry skin, hair loss, muscle weakness, weight gain, and fertility problems.

In my primary care practice, I’m finding that more and more of my patients are reporting feeling tired and concerned about whether they have hypothyroidism. Some patients request many different thyroid blood tests to diagnose and treat hypothyroidism. But are these tests really necessary?

How is hypothyroidism diagnosed?

Most major medical associations recommended diagnosing hypothyroidism through a blood test using a simple two-step approach.

  • First, we check the level of thyroid stimulating hormone (TSH), which the pituitary gland in the brain releases to stimulate thyroid hormone production.
  • If TSH is high, we confirm low thyroid function with a test called free or unbound T4 (T4 in the bloodstream that is not attached to a protein).
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It may help to think of the pituitary gland as a thermostat and the thyroid gland as a heater. The thermostat senses low temperatures outside of the body and turns on the internal heater. When body temperature reaches a set threshold, the thermostat signals the heater to stop working. In the body, it is the TSH produced by the pituitary gland that signals the thyroid to make more T4. When there is less free T4 in the blood, the pituitary senses the low levels and starts making more TSH.

Why not check thyroid hormones directly?

Why not check the thyroid hormones (T3 and T4) themselves, to see if the gland is not functioning properly?

The thyroid only makes small amounts of T3. Even in cases of severe hypothyroidism, T3 levels don’t go down that much. T4 is produced in large quantities by the thyroid. However, TSH is a far superior screening test because small changes in T4 cause large TSH spikes. Usually when a person has hypothyroidism, TSH levels become very high way before T4 levels fall below normal. So, in our analogy, the thermostat is very sensitive to small variations in temperature.

That’s why a normal TSH almost always means the thyroid gland is healthy and producing enough thyroid hormones. Research finds that a simple TSH test is enough to identify hypothyroidism in 99.6% of the tests performed.

You may have heard of expanded or full thyroid panels, which often include tests for TSH, total T3, total T4, free T3, free T4, anti-TPO antibodies, thyroglobulin, and reverse T3. There is no evidence these extra tests help to diagnose and manage thyroid disease, although they definitely add to health care costs. Proponents of expanded thyroid analysis believe more data may support a personalized intervention plan. However, what happens in a lab test often fails to mirror the elaborate dance of hormones in the body. Additionally, findings are highly variable. What happens in your body today may change in a matter of days or weeks, even without significant interventions.

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How is hypothyroidism treated?

To make matters even more confusing, we still do not recommend universal treatment for people who have subclinical hypothyroidism: slightly elevated TSH (between 4.12 and 10 mU/mL) and normal free T4.

Even though subclinical hypothyroidism is associated with worse health outcomes, treatment with thyroid hormone medicine may not significantly improve a person’s symptoms and quality of life.

From my perspective, more lab testing may cause anxiety, generate further tests, and lead to unnecessary treatment, which can cost hundreds, and sometimes thousands, of dollars. We have good solid evidence to support simple tests to diagnose hypothyroidism and follow people who need treatment for it. I recommend questioning any doctors (and bloggers) who recommend tests that are not supported by clinical research. While it may sound like a good idea to check more biomarkers, it’s important to understand the limitations of weak evidence before embarking on this journey. On some of these websites, dollar signs are just a click away.

The bottom line

According to most guidelines, a TSH below 10 provides good reassurance that a person does not have hypothyroidism.

If you are diagnosed with subclinical hypothyroidism and you do not want to take thyroid hormones, it’s reasonable to recheck TSH and free T4 in two to three months to see if any changes have occurred.

If your main concern is your energy level, eating a healthy whole food diet, exercising more, reducing stress, and sleeping well can help. What’s more, this approach may improve many chronic health problems — and it certainly will not deplete your bank account.

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