The 6 Thyroid Blood Tests (plus one you probably haven’t done)

When you experience symptoms, such as extreme fatigue, weight gain, low or no libido, and dry skin, and you go to see your doctor, your doctor will likely suspect your thyroid gland to be at the center of the symptoms.  

Your doctor will order blood tests to determine if the thyroid gland is not working as it should.  But unfortunately, many doctors seem reluctant, or some even outrightly refuse, to do a full work-up of the thyroid gland function.  

This can be a problem, as you cannot appropriately treat a person if you do not have all the facts at hand.  This means that there are at MINIMUM six blood tests that must be performed when you suspect an issue with the thyroid gland.  

Back in 2003, when I was first diagnosed with an underactive thyroid, my doctor only did the TSH and T4 tests, which indicated hypothyroidism.  But the doctor didn’t investigate further to determine WHY my thyroid was not functioning the way it should.  And even in this day and time, few doctors actually do. 

Here are the 6 thyroid blood tests that you should do when you suspect that your thyroid gland is not working as well as it should.  

The 6 Key Thyroid Tests

To understand the full story that your thyroid gland is trying to tell you, you have to do at least these 6 thyroid tests:

  1. TSH
  2. Total T4
  3. Free T4
  4. Free T3
  5. TPO antibodies
  6. TG antibodies


Let’s have a quick look at why each of these tests is important. 

Image by los-muertos-crew via


TSH (thyroid stimulating hormone) is produced by the pituitary gland and this hormone literally instructs the thyroid gland to produce thyroid hormones.  

When the TSH level is high, it may indicate that the thyroid gland is not producing enough thyroid hormones.  It is as if the body is asking for thyroid hormones, and the pituitary gland is sending the instruction to the thyroid gland to make more thyroid hormones, but the thyroid gland is not responding.  This is often the first indicator of hypothyroidism. 

When the TSH level is low, it may indicate that the thyroid gland is producing too many thyroid hormones.  This is not a healthy situation to be in either.  This can be the first indication of an overactive thyroid or hyperthyroidism.  

In some cases, a low TSH may be due to an abnormality in the pituitary gland, which prevents it from making the TSH hormones, and as a result, the thyroid gland is not making enough thyroid hormones either.  

If you are doing a repeat TSH test and you have been taking T3 hormones, your TSH results may be very low.  This is nothing to worry about because you are taking T3 hormones.  

Always do the sensitive TSH test, which will require you to fast for 12 hours before you do the test.  Also, take your blood test between 08h00 and 09h00 in the morning, as that will give you the most accurate results. 

Total T4

The thyroid gland produces both T4 and T3 hormones.  T4 hormones contain 4 iodine atoms, while T3 hormones contain 3 iodine atoms.  The key difference between these two hormones is that T4 hormones are inactive and not available for the body to use, while the T3 hormones are active and available for the body to use.  

The thyroid gland doesn’t produce equal amounts of T4 and T3 hormones.  It makes mostly T4 hormones (estimated at 94%) and little T3 hormones (estimated at 6%).  

The TOTAL T4 test measures the total number of thyroid hormones that are in your blood.  Some of the T4 hormones are bound to a protein as it is transported through the blood, and it is not available for the cells to use.  And then T4 hormones are FREE, meaning it is not bound to a protein, and the cells can use it for metabolism and other needs. 

When TOTAL T4 is low, it may be that the thyroid gland is not producing enough thyroid hormones, or that the pituitary gland is not giving instruction to the thyroid gland, which, as from above, may indicate a problem with the pituitary gland. 

The next test, the FREE T4 test, is the next piece of the puzzle. 

Free T4

FREE T4 (FT4)is looking at the number of T4 hormones that are available for the cells to use.  These are also the number of T4 hormones that are available for the body to convert to the active T3 hormones, which the cells can then use.  

A high level of Free T4 indicates hyperthyroidism (over-active thyroid), while low levels of Free T4 is indicative of hypothyroidism (underactive thyroid).

You can now start to create a picture of what is going on:

  • When you have a high TSH and a low FT4, it indicates hypothyroidism.  The body is asking for more thyroid hormones, the pituitary gland is giving the instructions, but the thyroid gland is not producing enough.


thyroid hormones
Image by drmicrobe via
  • If you have a low TSH and a low FT4, it indicates hypothyroidism due to the fact that the pituitary gland is not giving the right instructions.  This may indicate a problem with the pituitary gland. 
  • If you have low TSH and a highFT4, it is indicative of hyperthyroidism (overactive thyroid).  The thyroid gland is producing too many thyroid hormones without instruction from the pituitary gland.  This could also be an indication of the autoimmune condition, Grave’s Disease.  


Many conventionally trained doctors will only test TSH and Free T4.  They do not believe that it is necessary to check for T3 levels or even do antibody tests.   I believe you should definitely get the following tests done as well, as only then can you get all the pieces of the puzzle that is your thyroid health. 

Free T3

So why should we measure the Free T3 hormones? 

Simply, the T3 hormones are the hormones that are active and that can be used by the cells for important functions, such as metabolism and energy production.  But before the cells can use these hormones, the body has to convert the inactive T4 hormones into the active T3 hormones.  This conversion happens in a few places in the body, but mainly in the liver, followed by the gut.  

You can have more than enough T4 hormones, but if your body is struggling to convert these T4 hormones into the active T3 hormones, you can experience debilitating symptoms.  

This is why it is important to check the Free T3 levels as well: it is fine if your Free T4 levels are in “normal” levels, but your body is not converting them into the active T3 levels.    Many doctors simply look at the TSH level, and if the TSH is too high, they prescribe synthetic T4 hormones (because the body is obviously asking for more T4 hormones, right?)  

But what if there is a problem with converting the T4 hormones into the T3 hormones?  Then prescribing more T4 hormones is not addressing the issue.  Your body is still not converting the hormones, and simply adding more T4 hormones is not going to solve the problem.  

TPO Antibodies

TPO (thyroid peroxidase) is an enzyme that plays a role in the production of thyroid hormones.  

The TPO antibodies (TPOab) test is a blood test to see if the immune system is attacking TPO (therefore, attacking the thyroid gland).  

If the antibodies are present, it may indicate that you have an autoimmune disease.  Just be aware that the TPOab level could also be low or absent.  Be aware that should this happen, it only means that you don’t have antibodies present at the time of the test.  It, unfortunately, cannot exclude an autoimmune disease. 

TG Antibodies

TG stands for thyroglobulin, and it is the protein that the thyroid gland uses to make thyroid hormones.

The TG antibody test (TGab) is important as it can indicate that you have the autoimmune condition, Hashimoto’s Thyroiditis.  Research has also shown that patients that experience debilitating symptoms also have associated high levels of TG antibodies!

Again, be aware that if you don’t have antibodies present, it just means you don’t have antibodies present at the time of the test.   It does not exclude an autoimmune condition.  

The other lesser known test: Reverse T3

In some cases, it may be worthwhile to test for Reverse T3. 

What exactly will this help with?

We now know that the body converts the inactive T4 hormones into the active T3 hormones.  In times of major trauma, surgery or severe chronic illness, the body could convert the T4 hormones, not in the active T3 hormones, but into the useless Reverse T3 hormones.  These Reverse T3 hormones takes up space and blocks the use of the T3 hormones by the cells.   

Here is where this test could prove valuable:  if you are taking thyroid medication, but you are still not feeling better, it can be of value to see if your body is converting T4 hormones into Reverse T3 hormones.  Check the ratio of Free T3 to Reverse T3.  A low ratio could indicate that the body is trying to conserve energy to fix a problem.

There are two problems with this test: 

  1. It is very expensive, and some labs do not offer it.  When I requested it, the doctor whom I was with at the time didn’t even know about it, and then the lab also didn’t offer it.  We had to use a different lab.  Also, it is very expensive, and my medical aid didn’t cover it, so I had to pay for it out of my own pocket.
  2. There is controversy around the value of this test.  The available research has been done in an intensive care unit, not any outside of that.  So some believe that there isn’t value to patients who are not in an intensive care unit.


If you want to do this test, I recommend you discuss it with your doctor.  

If your doctor is not listening to you

I believe that the doctor-patient relationship should be based on mutual trust and respect.  Doctors play an important in our healing journeys, and I have found that my doctor has been an amazing source of information and guidance.  My doctor also respects me, in trying to understand my experience and the challenges of living with an autoimmune condition.  If I come up with a suggestion, she is willing to listen and learn, and even try new things.  

So what happens if your doctor is not willing to listen?  

If you cannot have an honest chat with your doctor, if your doctor is not willing to listen, if your doctor dismisses your experience (which is called gaslighting – making as if it is in your head) or is condescending, you have a problem.  It may be time to search for a different doctor who is willing to listen to you and build a relationship based on mutual respect.  

I have changed doctors a few times, and that includes two endocrinologists.  The one endocrinologist told me that I am picking up weight because I am not watching what I am eating!  That was despite that I was on a strict eating protocol at the time!  You guessed it: I didn’t go back to him.

In Conclusion

Your thyroid gland can really mess up your life.  If you are suspecting issues with your thyroid gland, please consult with your doctor to have your thyroid hormone levels tested.

Then, make sure that you test for the full thyroid panel, which includes TSH, Total T4, Free T4, Free T3 and both antibody tests.  

Adele du Rand

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