Absolute Must Have Lab tests for Thyroid Function

by integrativethyroid

There are several lab tests which are helpful in order to assess thyroid function. My TSH kept coming back normal for years but it turns out I had Hashimoto’s Thyroiditis. Hashimoto’s disease is an autoimmune disease where your body attacks its own thyroid tissue. My endocrinologists, and there were several, kept telling me everything was fine. But I wasn’t. I had all the classic hypothyroid symptoms like weight gain, cold hands and feet, hair fall, fatigue, brain fog and more.

The necessary lab tests for thyroid function, in my opinion are Free T3, Free T4, TPOab, TGab, Reverse T3 and TSH. We’ll get into the specifics of each below but these are the minimum for a doctor to order.

Please note that I am not a medical doctor. This opinion is based on my own personal experience with Hashimoto’s disease. 

Hashimoto’s Disease is the Number 1 Cause of Hypothyroidism

Not only is Hashimoto’s Disease the number one cause of hypothyroidism in developed countries (vs iodine in underdeveloped ones), it goes largely undetected in the wider public because endocrinologists will only order TSH as their (only) tried and trusted thyroid function indicator. But this is one sided in my opinion. Many people will get diagnosed with clinical hypothyroidism only once the rogue antibodies have destroyed their thyroid tissue to a level which pushes TSH out of normal lab ranges. It’s almost negligent.

You should find an endocrinologist who has experience with treating Hashimoto’s disease and is willing to order a full panel of thyroid labs for you. In addition, they should be listening to your symptoms and how you feel as the most important indicator of thyroid function. I would find a new thyroid doctor if your current one is telling you that high thyroid antibodies are normal and that you should take a “wait and see” approach.

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Other Tests to Determine Thyroid Health

Besides the lab tests mentioned above and below, getting a thyroid ultrasound if you have hypothyroid symptoms, abnormal lab ranges for the tests or feel lumps in your neck is a very good idea. Further testing for hormones (estradiol, testosterone. prolactin and DHEA), vitamins (B12 and D) and iron will provide further insights.

Essential Lab Tests for Thyroid Function

Free T4  (as opposed to Total T4) – Free T4 measures a level of the main thyroid hormone that circulates in the blood (aka thyroxine) which is not bound to proteins. It is able to enter and affect the body’s tissues. Integrative and functional practitioners will likely tell you that an optimal Free T4 should fall in the upper half of the lab range. T4 must be converted to T3 in the body, the active and usable form of thyroid hormone. The thyroid only produces roughly 20% of T3. The rest converts via various ways, one being by the liver.

Free T3  (as opposed to Total T3) – Free T3 measures a level of thyroid hormone (aka triiodothyronine ) that is not bound to proteins. It is able to enter and affect the body’s tissues. T3 controls how your body stores and uses energy (metabolism) along with many other crucial functions. This more accurately depicts how the thyroid is functioning. Integrative/functional practitioners will tell you that an optimal Free T3 should fall in the upper quartile of the lab range.

TSH (Thyroid Stimulating Hormone) – This measures how much of the stimulating hormone is in your blood. Many endocrinologists will tell you a TSH between .4 and 4.0 mu/L is normal. However, is is thought that most people feel optimal when TSH is below 2.5 mu/L. TSH is not an indicator of the tissue bioavailability of active T3, so a normal TSH can still mean that a patient feels sluggish and with hypothyroid symptoms.

Reverse T3 or RT3 – a sort of inactive thyroid hormone. A percentage of T4 also converts into reverse T3, the inactive form of T3. It competes with T3 at a cellular level and is considered a natural ‘buffer’ against thyroid overactivity. When RT3 production increases relative to T3 levels, this may cause a problem and produce hypo like symptoms. Remember it is normal to produce RT3 but it should be in a healthy ratio to T3. Testing for RT3 is good when all else is coming back normal and you still have hypothyroid symptom. RT3 over production can happen when stress levels are high. It can also occur when there is poor regulation of sugar or insulin resistance, nutritional deficiency and/or yo yo dieting.  Some medications can increase the production of T4 into Reverse T3.

Next, let’s talk Lab Tests for Thyroid Antibodies.

According to the American Thyroid Association:

“The immune system of the body normally protects us from foreign invaders such as bacteria and viruses by destroying these invaders with substances called antibodies produced by blood cells known as lymphocytes. In many patients with hypothyroidism or hyperthyroidism, lymphocytes react against the thyroid (thyroid autoimmunity) and make antibodies against thyroid cell proteins. Two common antibodies are thyroid peroxidase antibody and thyroglobulin antibody. Measuring levels of thyroid antibodies may help diagnose the cause of the thyroid problem. For example, positive anti-thyroid peroxidase and/or anti-thyroglobulin antibodies in a patient with hypothyroidism result in a diagnosis of Hashimoto’s thyroiditis.”

So, the next two tests are crucial:

TPOab (Thyroid Peroxidase antibody) – should be within the lab range. 0 is best.

TGab (Thyroglobulin antibody) – should be within the lab range.

Levels can fluctuate in pregnancy and should be checked often.

best lab tests for thyroid function

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