Thyroid Function Tests – Understanding Your Blood Test Results

Their next episode in their “Understanding Your Blood Test Results” series is all about the thyroid and the tests you can do to check if your thyroid gland is functioning properly. Dr Sandra Cabot and naturopath Margaret Jasinska explain TSH, T4, T3, antibody and iodine testing and how to interpret the results. They also explain the many symptoms of thyroid dysfunction and that significant improvements can be made to thyroid health through dietary changes and supplementation.

Listen to my podcast and leave a comment below if you have any questions.

DR CABOT: Hello, everyone. Great to be with you today. We’re talking about understanding your blood test for thyroid function. And we’re joined by my colleague, Margaret Jasinska.

MARGARET: Hi, Dr Cabot. It’s great to talk about this topic because it interests just about all of our patients. Everyone wants to know what their thyroid is doing and whether it’s functioning normally.

DR CABOT: Well, they’re smart. And Margaret and I have co-authored a book on thyroid problems, which is a very helpful resource for you. But we see a lot of people with thyroid disorders because it’s the most common autoimmune disease of all. And we see a lot of people who are trying to optimize or tweak their thyroid function with nutritional supplements or with thyroid hormone. And so, they have regular blood tests for thyroid function. And it’s good to understand what you’re looking at.

MARGARET: Absolutely! And it is possible to make significant improvements in your thyroid function, even just with nutritional supplements and diet changes. And blood tests are great because we’ve got proof. We can prove that what you’re doing is working.

DR CABOT: That’s right. Blood tests are very accurate for hormones, by the way. A lot of people say, “Oh, no, they’re not. You’ve got to have saliva tests or urine tests.” No, the blood tests are done using nuclear medicine, radioimmunoassay and they’re very accurate. And they’re usually much cheaper, which is handy.

But the first thing we look at is your TSH, which stands for thyroid stimulating hormone, TSH. And that is produced by your pituitary gland and secreted into the bloodstream. And it travels to the thyroid gland to stimulate your thyroid gland to make more thyroid hormone. That’s why it’s called thyroid stimulating hormone.

So often, the first sign of a sluggish or underactive thyroid is elevated TSH, because your hypothalamus is telling your pituitary gland, “Wake up the thyroid! Tell the thyroid to make more thyroid hormone!” So, the pituitary sends out more and more thyroid stimulating hormone to try and get your thyroid gland to make the thyroid hormone.

MARGARET: Exactly. Trying to wake it up. So, if your thyroid is sluggish, that TSH hormone can go higher and higher.

DR CABOT: It can. And normally it shouldn’t be higher than 5.5. Some laboratories will vary and say it shouldn’t be higher than 4. So, it’s not categorical. But ideally, we like to see the thyroid stimulating hormone around 2.5 to 3.

MARGARET: Yes, that’s a perfect level.

DR CABOT: That’s ideal. So, what happens if your thyroid is overactive and it’s making way too much thyroid hormone? Well, then your pituitary gland will go, “Oh-oh, this isn’t right!” So, it’ll stop making the thyroid stimulating hormone, and you’ll have very, very low levels of thyroid stimulating hormone. It’ll be like 0.001 or something when it should be at least point 5. If it’s below point 5, it’s too low, which means your thyroid is overactive.

So, it’s a really good test, the TSH. It’ll tell us whether your thyroid is over or underactive.

MARGARET: Yes. And in the book that we wrote together, “Your Thyroid Problems Solved”, there is a table with all these hormones and possible scenarios and explanations for why.

DR CABOT: Yes. And so, if your thyroid stimulating hormone is too high, it means your thyroid is underactive. Sometimes, all you need to do is take some selenium and iodine, vitamin D, zinc and you’ll get your thyroid gland working beautifully again. And the thyroid stimulating hormone will come down showing that your thyroid hormone production has increased. Often, that’s all you need to do. Maybe look at your diet. A lot of people with underactive thyroid problems are gluten intolerant.

MARGARET: Yes, because autoimmune disease, Hashimoto’s thyroiditis, is the most common autoimmune disease in the world. And it’s the most common reason that your thyroid gland may struggle to make enough hormones. So, the immune system produces antibodies that actually attack the thyroid gland, so it can’t make enough hormones. And for some genetically susceptible people, eating gluten can trigger that autoimmune attack on the thyroid. And removing gluten from the diet can help to normalize thyroid function. For some people, just getting rid of gluten from their diet is all they need. For other people, they have other complicating factors, like nutrient deficiencies, like gut health problems, like gut bug imbalances. So, some people need a bit more help and work to restore their thyroid health.

DR CABOT: And we see a lot of people who are deficient in iodine. We test it in the urine. So, if your urinary iodine is less than 100 in concentration, then you’re going to need to take some iodine. So, you can take something like the Thyroid Health capsules, which have iodine, selenium, vitamin D and zinc.

We see a lot of people who are selenium deficient, as well. Although blood tests really are not an accurate indicator. So, we usually would give some selenium, if people have elevated thyroid antibodies to lower their antibodies.

So, if you have a family history of thyroid problems or you yourself have an imbalance in your thyroid function – shown on a blood test – you should be tested for thyroid antibodies. And we look at antithyroglobulin antibody. And we look at antithyroidal peroxidase antibodies. So, they’re big names. You don’t have to remember them. But they’re just antibodies, and they should be less than 60. If you have high levels of antibodies, that means your thyroid gland is being attacked by these antibodies, and they’re like little missiles. They will find your thyroid, they’re like thyroid-seeking missiles. They will find your thyroid and destroy it. And your thyroid will become very, very diseased and unable to produce thyroid hormone.

So, it’s good to check for these antibodies early on. Often, if there’s a family history of thyroid disease, we’ll look at antibodies in teenagers to see if they’re developing the disease.

MARGARET: Yeah, exactly.

DR CABOT: And we can get them down often with the change in diet and with supplementing with selenium, iodine and keeping the vitamin D level up. Very simple, safe things.

Now, as far as other blood tests for thyroid, we can check the level of thyroid hormones in your blood. And we look at a hormone called T4 or thyroxin. And that should be between 11 and 22. And we look at the other thyroid hormone, T3, which is known as triiodothyronine, and that should be between 3.5 and 6.5. So, we can check everything. We can check the thyroid stimulating hormone from your pituitary gland. We can check the hormones that are being made by your thyroid gland, which is your T4 and your T3. And we can get a total picture of your thyroid. And we also check the antibodies, if we’ve got any suspicion that you’ve got autoimmune thyroid disease.

MARGARET: So, it’s important to request more than just TSH. Because many doctors, if you ask for a thyroid blood test, they’ll only order TSH. But it doesn’t give very much information at all. So, it’s important to request these other tests.

DR CABOT: It is! Especially the antibodies, because if you can pick up that you’ve got antibodies attacking your thyroid, even before your thyroid becomes underactive, well, you may be able to prevent the Hashimoto’s. And you’re going to feel a lot better if you prevent that, because it makes you very tired.

MARGARET: Yes, yes.

DR CABOT: And you’ll put on weight, if your thyroid is underactive. You’ll really struggle to lose weight.

The other thing, if we want to get really sophisticated, we can check the shape of your thyroid hormone. That’s pretty sophisticated.

MARGARET: That sounds strange.

DR CABOT: Because it’s not only important to have the right amount of hormone in your blood, it’s important to have the right shape of thyroid hormone. So, the T3, which is the triiodothyronine – the T3 hormone – is the most active hormone. But it needs to be the right shape to work on your cells. So, we can test its shape. That’s called reverse T3. And if it’s the reverse shape, like a mirror image, then it won’t work. So, if you have high levels of reverse T3, then that would explain why your thyroid hormone medication isn’t working.


DR CABOT: Because a lot of people take thyroxine tablets and that is prescribed by most doctors. And that’s T4. And that’s got to be converted into the active form of T3 to work in your body. But if you’re converting it to the wrong shape, the reverse T3, then you’re going to stay feeling like your thyroid is underactive and you won’t be losing weight. So that’s when we can check the reverse T3 for you. And if you’ve got high levels of reverse T3, we can help your liver and your gut to make the right shape thyroid hormone. Once again, we need to use selenium, and we need to improve your liver function. And we need to look at your gut bugs.

MARGARET: Yes. Because gut toxicity, inflammation, insulin resistance, they are common conditions that can cause excess reverse T3. So, you don’t have enough of the active T3, and your metabolism can suffer.

DR CABOT: That’s right. So, to really understand your thyroid completely, you need a TSH thyroid stimulating hormone. You need your levels of T3 and T4 thyroid hormones done. Your reverse T3 and a urinary iodine concentration and your level of thyroid antibodies. Now, you may not get the reverse T3 on Medicare. Most countries you don’t, but it’s not prohibitively expensive. And if you’re really struggling with your thyroid, it’s worthwhile having. Because if we can fine tune your thyroid, you’ll feel 100 times better and your weight loss will be a lot easier.


DR CABOT: Thanks for listening!