Understanding Your Thyroid Labs: Dr. Sean Breen Explains

One of the things I love to do is teach patients about physiology and really get them to understand their blood work. Thyroid studies are the most intricate and require the most in depth discussion with my patients. Let me try and explain them here so it makes sense to the average person.   

The thyroid gland sits in the center of the front of the neck on either side of the trachea (windpipe). It’s main function is to regulate our metabolism and control temperature in the body. There is not one cell in the body that is not effected by thyroid hormone. How efficiently the body digests and converts an apple into energy is dependent on an efficient thyroid gland. How the cell utilizes every hormone and nutrient is dependent upon thyroid hormone.

When the average family doctor checks your thyroid he typically checks something called the TSH test. TSH stands for Thyroid Stimulating Hormone and is a hormone that is produced by the pituitary gland in the center of the brain. It’s main function is to tell the thyroid to make thyroid hormone, hence the reason it is called thyroid STIMULATING hormone. The pituitary gland senses how much thyroid hormone is in the bloodstream. If the circulating level of thyroid (T4 and T3) are low then the TSH goes UP because the brain is sensing that the thyroid needs to make more thyroid. So in patients that have HYPOthyroidism (under active thyroid), the brain senses that there is not enough thyroid hormone in the blood and the TSH goes up. The exact opposite occurs in patients with HYPERthyroidism (overactive thyroid). The brain senses that there is too much circulating thyroid hormone (T4 and T3) and the brain slows down production of TSH, hence the TSH goes down or is low.

So to recap: TSH is HIGH is HYPOthyroidism and the TSH is LOW in HYPERthyroidism. Are you with me thus far?

The range for TSH in the blood is 0.45-4.5. The endocrinology community used to set the upper limit for TSH at 10, then it was lowered to 5 and now most doctors want to keep the TSH at 2.5 or below.

Before I comment more on the TSH let me explain a few more tests.

TSH tells the thyroid to primarily make two hormones. 80% of the thyroid made is T4 and 20% of the thyroid hormone is T3. Some doctors actually like to check the level of T4 and will order that test as well. The range in the blood is typically 0.85-1.79. In patients who have HYPOthyroidism it would be low because the thyroid gland is not making enough hormone. In HYPERthyroidism the T4 will typically be high.

Now that you learned about TSH and T4, I want to spend some time talking about the MOST IMPORTANT thyroid test that your doctor probably didn’t order. The free T3 (triiodothyronine) is the most important test because T3 is the only metabolically active hormone. That means it is T3 that has an effect on a cellular level and determines whether or not you are symptomatic. Let me point out that 80% of the thyroid that is made is T4. The obvious question then is why does the thyroid produce so much T4 is it is the T3 that effects the cell. The first answer is that it is primarily T4 that can cross into the brain and have an effect on brain cells. T3 generally does not cross the blood brain barrier. What the body does though is it converts the majority of T4 to T3 AFTER the thyroid gland secretes it. So it is the free T3 that we really need to look at when looking at thyroid studies and evaluating someone for thyroid disease.

The range for free T3 in the blood is 2.0-4.4. That means that 95% of people will have a free T3 that falls within this range.

Most doctors will tell patients that their thyroid is normal if their TSH is normal. They won’t even look at the free T4 or free T3. The reason why this is flawed is because you can have a perfectly normal TSH and have a free T3 that is low. So your doctor incorrectly diagnoses you with a normal thyroid when in fact you need thyroid badly.

If a patient comes to me with symptoms of hypothyroidism (cold hands/feet, tired, fatigued, constipated, can’t lose weight, is losing hair, has thinning eyebrows and is depressed) I focus on the free T3. If the free T3 is not in the upper range of normal (4.0-4.4) then I treat them with thyroid (Armour or compounded dessicated thyroid which is T4 AND T3). Generally, patients do not feel better until their free T3 is in the upper range of normal. I can not tell you how many patients I see who are cold, tired and fatigued who are told their thyroid is normal when in fact they need thyroid and feel incredible when I treat them.

Some doctors like myself will also check for antibodies against the thyroid gland. One common reason for an under or overactive thyroid is the bodies immune system attacks the thyroid gland (Hashimotos Thyroiditis or Graves Disease). Identifying auto-antibodies against the thyroid does not change management as far as prescribing thyroid, but it does clue the physician into other things to focus on. For example the patient may have gluten intolerance which is triggering the immune system to be overactive.

The main point I want to make is this: DEMAND your doctor checks your free T3. If is not optimal (4.0-4.4) and you have symptoms then you will benefit from taking armor thyroid or compounded dessicated thyroid. If he or she is not willing to treat you please contact me through my website, www.BreenCenter.com and I will schedule a time to meet with you.