Thyroid Function Tests

Everything You Need to Know About Thyroid Function Tests

As we know that thyroid function tests are very important but before we go inside the tests, let’s have a look at how thyroid works in our body. Without this knowledge, learning about thyroid function test would be useless. TFTs can be a confusing topic for a lot of reasons! The interpretation of TFTs superficially seems like it should be very easy, and in the majority of patients, it is. However, a significant minority of TFTs don’t conform to what logic suggests. The biosynthesis of thyroid is unusually complex. Even the terminology regarding TFTs is very confusing. For example, “thyroid hormone” generally refers to 1-2 specific and nearly identical compounds, there are a total of 4 hormones directly involved in regulation of thyroid gland activity. The only way to know about the status of your thyroid is to visit your nearest walk in clinic in London and consult with GP about your blood test. Let’s get into each of them.

Thyrotropin releasing hormone (TRH)– this is a Tripeptide amide which essentially means it is composed with 3 amino acids. It forms in the hypothalamus and travels to the anterior pituitary via the hypothalamic-hypophysial portal system. The primary effect of TRH is to stimulate the release of TSH. 

Thyroid stimulating hormone (TSH)- it is a glycoprotein. It has a number of different specific effects, all of which is focused on increasing the physiologic actions of thyroid hormones. Under primary effects, they increase the release of preformed thyroid hormone and  increase the rate of thyroid hormone formation and also to increase the size and number of thyroid cells. 

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Thyroid hormones 

Let’s talk about true thyroid hormones that is those hormones that are actually synthesized and released by the thyroid glands. They are called as T3 (triiodothyronine) and T4 (thyroxine). As we said earlier that the synthesis of T3 and T4 is very complicated but requires tyrosine and iodine. The tyrosine used for thyroid hormone is actually stored as a glycoprotein called thyroglobulin, each molecule of which has about 70 molecules of tyrosine. 

The thyroid gland is relatively unique among endocrine organs in its ability to store large amounts of preformed hormone. In normal physiological condition, in response to TSH, the thyroid secretes predominantly T4 along with a small amount of T3. after they are released, over 99% of the thyroid hormones are bound to plasma protein in the circulation.

Thyroid function tests 

Now that we know how thyroid glands work, let’s talk about thyroid function test. TFTs are complicated due to the variety of substances which can be measured, and the variety of specific assays that different labs can use. The only three tests which are commonly checked are TSH, free T4 and to a lesser extent free T3. we typically order for T3 when we are specifically concerned about hyperthyroidism because it will be more sensitive. Based on our current understanding of the thyroid disease and current lab technology- TSH, free T4 and free T3 are more less the only choice under the domain of thyroid function tests that you ever need to order. 

Some of these other tests which are available for commercial purposes and sometimes used only for research include the following: 

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Rarely ordered TFTs 

  • Total T4 and T3
  • T3 resin uptake
  • Reverse T3
  • THS
  • Thyroxine binding globulin
  • Thyroglobulin

Together these tests could be used to estimate free T4 and free T3. these calculations are called the free T4 or T3 index. Another rarely ordered test is the reverse T3. it was once invoked  to distinguish the true thyroid disease from TFT abnormality caused by non thyroid illness. Next is TRH, the reason for not ordering might be because of the non availability, not validated for clinical use, generally not helpful or all three.  

Thyroid blood tests 

Thyroid function tests are done most commonly by people. The test are successful in explaining if you have thyroid in underactive state. Make a blood test appointment at our walk in clinic and get your doubts cleared in the first place . People do find the test result as confusing and wonder what “normal” means.

What does “normal” means in a report? 

When the report states normal to some individual, it doesn’t mean you will have the same range counted as being normal. Normal ranges have been onto the show for quite a long time. It helps people understand about the accurate status of your health. In older times, disease were categorised as having severe forms or just normal. 

As the science advanced and people have now been secured enough with the deadly diseases, the reports stating their health conditions have also changed.

Is the normal report same for everyone? 

The straight cut answer is NO! In order to find out if your thyroid gland is working just fine, you have to go through a test which is called as TSH. the test can very well detect if your thyroid level is overactive or underactive. TSH (thyroid stimulating hormone) is actually a hormone in your blood and the test will justify how much of it is there in your blood. The normal value of TSH levels is 0.4 to 4.0 milli-international units per liter. If you have any thyroid disorder then your normal range will be somewhere between  0.5 to 3.0 milli-international units per liter. 

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The report that states normal for you might not be normal for some other individual. In fact, if you are having reports that states normal, it can be changed anytime in the future as well. The reason behind this is, you may tend to change your dietary regime or you may have drastic change over your stress levels. These factors play an important role in deciding your report status.