Will Thyroid Cancer Show up in Blood Work?

Thyroid cancer is one of the most common types of cancer, especially in females. A common question arises as to whether you can identify thyroid cancer with your blood work, or labs. Because the thyroid is routinely tested during an annual physical exam and many other doctor visits, it would be very helpful if cancer could be identified during this routine testing. Sadly, it's usually not that easy. But let's review what tests are commonly offered, and which tests could be valuable. And explain why thyroid cancer usually can't be identified with blood work.

First, let's consider what labs are usually tested when you get your normal thyroid labs. For most people, a TSH (thyroid stimulating hormone) is the main test that is ordered. This test is not actually a test of your thyroid itself, but is instead a test of the body's perceived need for thyroid hormone. What does that mean? It means that when your body senses that there is a lack of thyroid hormone, then TSH is released from your pituitary gland. This TSH then interacts with the thyroid, and more thyroid hormone is released. TSH levels do not usually help us to know if a person has thyroid cancer, but they can give valuable insight into the status of your thyroid.

Thyroid hormone proper is usually the pre-active form (T4) or the active form (T3). Most people can convert from the inactive/preactive form of T4 into T3 as needed. These labs are also commonly ordered. While these levels are important to know if your thyroid is working and how it is affecting your metabolism, they also rarely show as signs of thyroid cancer.

At this point, let's pause because these are the most commonly ordered blood tests. Most people with thyroid cancer will not be able to see the cancer in their normal blood work. Why not? Because thyroid hormone is necessary to sustain life. And because it is so important, your thyroid has the capacity to produce much more thyroid hormone than it needs (usually- unless you have Hashimoto's Thyroiditis or another form of hypothyroidism). That means that, when a part of your thyroid begins to have cancer, the rest of the thyroid picks up the slack and your labs don't show that part of it isn't working right.

When would blood work show that you might have cancer? Well, if you have either Graves' disease or Hashimoto's thyroiditis, you are more likely to have thyroid cancer. And this means that if your thyroid is overactive or underactive, it is more likely that there is also a cancer. But that is different than showing that you actually have cancer via your blood work. In other words, there are labs that can suggest an increased risk, but they don't actually show that you have thyroid cancer.

Are there more specific tests that could show cancer? Yes, in some cases, a lab test or blood work can find thyroid cancer. One rare type of thyroid cancer is medullary thyroid cancer, and that can commonly be identified by the levels of calcitonin in your blood. That same type of cancer can be predicted based on certain genetic mutations that you might have. But that type of cancer is rare, and so this test is much less likely to identify disease that is caused by normal papillary thyroid cancer. There are also some newer tests that look for circulating tumor cells to identify if you have a thyroid cancer. Sadly, these are not yet ready for every-day useage, and rarely are effective at finding thyroid cancer.

In conclusion, thyroid cancer can usually not be found via your blood work. However, your blood work can give clues about thyroid health, and if your thyroid is either overactive or underactive, you are more likely to have thyroid cancer. Ask your doctor or set up a visit if you have more questions!