WHY TESTING TSH IS NOT ENOUGH
Did you know that up to 50% of thyroid disorders may go undiagnosed? The good news is testing TSH (and sometimes T4) is becoming more common in your doctors’ office. The bad news is that’s not enough, and here’s why.
TSH (THYROID STIMULATING HORMONE)
This hormone is the “gold standard” of thyroid tests. If your doctor just runs one test this will be it. TSH represents your overall thyroid function.
TSH is released from the pituitary and stimulates your thyroid to produce more thyroid hormone (T3 and T4). When your thyroid is under-active more TSH is released from the pituitary to try to increase the thyroid’s function.
- When TSH is high it indicates your thyroid is under functioning, and
- When TSH is low it indicates your thyroid is over functioning
The main problem with testing TSH is the large reference range. The range can vary based on the lab company, but typically 0.27 mlU/L – 4.2 mlU/L is considered “normal.” Above or below this range indicates hypothyroidism and hyperthyroidism, respectively.
Your thyroid gland is very tightly regulated, so small changes can have a big impact on how you feel. Therefore someone with a TSH of 0.5 mlU/L and another with a TSH of 4.0 mlU/L are both considered “normal” but they will likely feel different.
In fact, 95% of healthy individuals actually have a TSH of less than 2.5 mlU/L. Which is why at the very least you should be looking for a TSH below 2.5 mlU/L.
fT4 (FREE THYROID HORMONE 4)
In a conventional medical setting the second most common thyroid blood test is T4.
There are two main forms of thyroid hormones: T3 and T4. Both are released from the thyroid when it is stimulated by TSH.
- T4 is released in larger amounts and is the “inactive” form.
- T3 is released in smaller amounts and is the “active form.”
- T4 is converted to T3 when needed.
If your lab results show an abnormal TSH your doctor will typically follow-up by testing your T4. T4 has a longer half-life (stays in your bloodstream longer) than T3, so it is easier to test. But as we discussed above: T4 is the inactive form that gets converted to the active form (T3). So when we just test T4 we are assuming that your T4 is being successfully converted to the healthy form of T3.
That being said, T4 is still an important part of your thyroid assessment. Calculating the ratio of fT4 to fT3 is helpful to see how much fT4 is successfully converting to fT3.
By running just TSH and T4 many individuals with thyroid symptoms and less overt lab results can be missed. To better understand how your thyroid is functioning, more comprehensive thyroid testing is required. Starting with fT3.
fT3 (FREE THYROID HORMONE 3)
As discussed above, T3 is the active form of T4. It is the thyroid hormone that produces results in your body. Less T3, means less signals coming from your thyroid to the rest of your body. This can cause symptoms of hypothyroidism.
WHY DOES THE FORM OF T3 AND T4 MATTER?
There are multiple forms of T3 and T4 in your body. Thyroid test should be looking at FREE T3 (fT3) and FREE T4 (fT4).
TOTAL T4 is also available, but this includes both free T4 and bound T4. Bound T4 cannot be converted to fT3, so just looking at total T4 doesn’t give us an accurate picture of what’s happening in your body. Like total T4, TOTAL T3 includes both free T3 and bound T3. Bound T3 is not an active form, so total T3 also fails to give an accurate picture.
There is also another form of T3: REVERE T3. This is the fourth blood test that should be done when assessing your thyroid function.
rT3 (REVERSE THYROID HORMONE 3)
Like fT3, reverse T3 is also made from T4. But unlike fT3, rT3 is essentially inactive (like T4). rT3 looks a lot like fT3 so it can attach to the fT3-receptors and prevent fT3 from binding. If fT3 can’t bind, it can’t do it’s job.
HOW STRESS AFFECTS YOUR THYROID
rT3 production is increased during times of stress. Which means when you experience mental and emotional stress (from work, home, etc.), physical stress (from over exercising, unhealthy dieting, etc.), or environmental stress (from toxins, heavy metals, etc.) your body isn’t getting enough stimulus from your thyroid and that can exacerbate your hypothyroid symptoms.
THYROID ANTIBODIES (Anti-TPO)
You may have heard of Hashimoto’s Thyroiditis. This is an autoimmune thyroid condition and actually accounts for 90% of all hypothyroidism. If you have an under-active thyroid and have not had your antibodies run, you should.
Like all autoimmune conditions, Hashimoto’s is your body having an immune reaction against itself (in this case your thyroid). We can see this on a blood test by looking at antibodies such as thyroid peroxidase antibodies (Anti-TPO). Once we know there is an autoimmune component to your condition we can treat this aspect as well.
That sums up the thyroid-specific blood tests. There are three more important blood test which should be run when assessing your thyroid function.
VITAMIN D
This test should come as no surprise. In Canada we have notoriously low vitamin D levels, especially during the winter. Vitamin D levels can have such a huge impact on your body – from bone health to mental health to thyroid function. In fact, those with autoimmune hypothyroidism actually have significantly lower levels of vitamin D than those without hypothyroidism. Get tested to ensure your blood levels are optimal!
The next two lab tests are important because hypothyroidism may not be the only condition contributing to your symptoms. Fatigue is commonly caused by a deficiency in B12 and/or iron. Addressing these deficiencies can have a meaningful impact on your energy levels and your overall symptom experience.
VITAMIN B12
Like vitamin D, deficiencies in vitamin B12 are common in hypothyroid patients. Research shows that up to 40% of hypothyroid patients may be deficient in vitamin B12. Low B12 levels often result in fatigue, numbness and tingling of your hand and feet, constipation, shortness of breath, muscle weakness, light-headedness, as well as issues with memory and cognitive function. Many of these symptoms overlap with symptoms of hypothyroidism. It is important to get your B12 levels assessed to determine if a B12 deficiency is playing a role in how you feel.
FERRITIN (IRON)
Iron deficiency can cause fatigue on its own, but it can also do so via the thyroid. Iron is necessary for the production of thyroid hormone and the conversion of T4 to T3. So, if you are deficient in iron it can exacerbate your hypothyroidism.
To test for an iron deficiency it is best to use a panel of tests to get the whole picture, but at the very least your ferritin (the storage form of iron) should be tested.
All of these tests, in combination, give a holistic picture of your thyroid’s function and can help direct your treatment approach.
To chat more about diagnosing and treating your thyroid dysfunction book a free 15 minute discovery session, here.
