I was 7 or 8 weeks pregnant with baby number four when I diagnosed myself with hypothyroidism. I had asked my medical assistant to draw blood because some bloodwork from the previous week with my obstetrician was a little off. When the results came back, the thyroid stimulating hormone (TSH) level was flagged in bright red. My level was high and I needed to start taking thyroid hormone.
After my son was born, I hoped I would be able to stop taking thyroid hormone, but as soon as I did my TSH rose back up into the abnormal range. It was clear that, pregnant or not, I had an underactive thyroid. I wasn’t surprised, exactly. After all, thyroid problems are very common, especially among women. Many of my patients have thyroid problems. Yet, there are certain aspects of thyroid disease that are confusing to people. So, let’s review the basics.
Thyroid tests
Perhaps the most confusing aspect of thyroid disease are the tests we use to diagnose and monitor thyroid problems. It’s an alphabet soup of acronyms that all start with the letter T with numbers that don’t always mean what we think they should. Here’s a breakdown.
Thyroid-Stimulating Hormone (TSH)
The main test used to screen for thyroid problems is the TSH. This hormone is made in the pituitary gland and tells the thyroid to make thyroid hormone. As a result, when TSH rises that means there is not enough thyroid hormone circulating. When it falls there is too much thyroid hormone circulating. Put another way, a high TSH is indicative of an underactive thyroid. A low TSH suggests an overactive thyroid. It’s an inverse relationship.
Thyroxine (T4) and Triiodothyronine (T3)
T4 and T3 are two versions of thyroid hormone that circulate in our blood. Human thyroids make T4, which then gets converted to T3 in the blood by enzymes that pluck an iodine atom off T4. T4 lasts a long time but isn’t very active. T3 is very active but lasts a short time. There are lots of versions of tests for T4 and T3, and some produce more accurate results than others. That is one reason why we use the more reliable TSH as a screening test.
Thyroid antibodies
The immune system can make four different antibodies that lab tests can measure. Thyroid globulin antibodies and thyroid peroxidase antibodies are both used to diagnose Hashimoto’s disease, an autoimmune inflammation in the thyroid that often leads to an underactive thyroid. In this case, the antibodies aren’t causing the inflammation in the thyroid, they result from it. Instead, it’s white blood cells called lymphocytes that inappropriately attack the thyroid. That attack causes thyroid cells to break down and the proteins inside get exposed to the immune system which makes antibodies to those proteins.
Testing for TSH receptor antibodies and thyroid simulating immunoglobulin helps us to diagnose Grave’s disease which causes an overactive thyroid. As their name suggests, these are antibodies made by the immune system that bind to receptors on thyroid cells and direct them to pour out thyroid hormone in an unregulated way.
This distinction between the role of thyroid antibodies in Hashimoto’s disease and Grave’s disease is important. It means that in Grave’s disease there is a direct correlation between antibody levels and how severe the disease is. However, in Hashimoto’s disease there is no connection between antibody levels and how severe the disease is.
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Hypothyroidism
An underactive thyroid is the most common problem with thyroid function and hypothyroidism is quite common. Data from the NHANES III study suggests that nearly 5% of people have an underactive thyroid and women are up to 10 times more likely than men to develop an underactive thyroid.
Most people with an underactive thyroid have Hashimoto’s disease. Their immune system attacked their thyroid and now it can’t make enough thyroid hormone. Other causes of hypothyroidism include surgery to remove part or all of the thyroid, and radioactive iodine ablation.
The treatment is always the same. We give thyroid hormone in pill form to provide the body with the thyroid hormone it would make if it could but can’t.
Hyperthyroidism
Having an overactive thyroid is much less common that having an underactive thyroid. Even by the most generous estimates only about 2.5% of people have hyperthyroidism and fewer than 1% of people will experience the most severe form of hyperthyroidism, Grave’s disease. An overactive thyroid can also be caused by thyroid nodules that churn out thyroid hormone in an unregulated way. Inflammation in the thyroid can also cause it to leak thyroid hormone, usually temporarily (more on that in a minute).
How we treat hyperthyroidism depends on what’s causing it. Grave’s disease can be treated with medication, surgery, or with a non-invasive procedure called a radioactive iodine ablation. If wayward nodules are causing the problem, radioactive iodine ablation or another procedure called radiofrequency ablation are often used to bring thyroid hormone levels back to normal. It can seem counterproductive to cause hypothyroidism when treating hyperthyroidism with surgery or radioactive iodine ablation. But hypothyroidism is much safer and easier to try. We are trading a challenging potential dangerous problem for a more straightforward one.
Thyroiditis
As I alluded to a minute ago the thyroid can become inflamed, and when it does it can release thyroid hormone and cause a temporary hyperthyroidism. Once the thyroid hormone gets metabolized, thyroid hormone levels often drop a little low before returning to normal.
A few different things can cause this including viruses (Covid-19 is notorious for this). It can also occur postpartum as the immune system is returning to normal after pregnancy. People with Hashimoto’s disease are more likely to develop some types of thyroiditis including postpartum thyroiditis.
Because thyroiditis typically gets better on its own, doctors don’t usually treat it. Though we will treat symptoms like pain and racing heart if patients are experiencing them.
Role of genetics
The biggest single factor determining whether you will develop thyroid disease, especially autoimmune thyroid disease is your genes. If your parents or siblings have thyroid problems your chances are increased. And both Hashimoto’s disease and Grave’s disease often run together in families.
But there are environmental factors at play too. Viruses or stress—both physical stress and emotional stress—trigger the autoimmune inflammation. But those triggers don’t always occur just before the thyroid stops functioning normally especially when it comes to Hashimoto’s disease. And we don’t typically identify the trigger in most cases. So, if you have a family history of thyroid disease it’s important to share that information with your doctor.
The Savvy Short:
There are several tests used to understand how well the thyroid is functioning including testing levels of TSH, T4 and T3. We will often also check thyroid antibodies associated with Hashimoto’s disease and Grave’s disease to better understand a person’s thyroid problem.
Hypothyroidism, or an underactive thyroid, is most often caused by Hashimoto’s disease. It is treated by giving thyroid hormone in pill form.
Hyperthyroidism, or an overactive thyroid, can have autoimmune causes but can also result from nodules in thyroid that make too much thyroid hormone. Treatments for hyperthyroidism depend on what is causing the problem.
The biggest factor in whether someone will develop a problem is their genetics. If you have a family member with thyroid disease, tell your doctor so they can monitor your thyroid function.
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