Thyroid, underactive - Diagnosis 

Diagnosing underactive thyroid 

How thyroid hormones work 

  • When thyroxine levels fall, thyroid-stimulating hormone (TSH) is released in the blood to stimulate the production of thyroxine.

  • When thyroxine levels are too high, TSH production drops to allow thyroxine levels to return to normal.

Medical terms

Hypothyroidism: an underactive thyroid.

Thyroxine: a hormone produced by the thyroid, also called T4.

Overt hypothyroidism: where you have clear symptoms of an underactive thyroid.

Subclinical hypothyroidism: where your symptoms are mild or barely noticeable.

Levothyroxine: tablets containing the hormone thyroxine, used to treat an underactive thyroid.

If you have symptoms of an underactive thyroid (hypothyroidism), see your GP and ask for a blood test.

Find out more about the symptoms of underactive thyroid.

A blood test measuring your hormone levels is the only accurate way to find out if there is a problem.

The test, called a thyroid function test, looks at levels of thyroid-stimulating hormone (TSH) and thyroxine in the blood.

A high level of TSH and a low level of thyroxine hormone in the blood could mean you have an underactive thyroid.

If your test shows raised TSH but normal thyroxine, it means you may be at risk of developing an underactive thyroid in the future.

Your GP may advise a repeat blood test every so often to see if you eventually develop an underactive thyroid.

For more information on testing, go to Lab Tests Online: thyroid function tests.

Referral

Your GP may refer you to a specialist in hormone disorders, known as an endocrinologist, if you:

  • are younger than 16
  • are pregnant or trying to get pregnant
  • have just given birth
  • have another health condition, such as heart disease, which may complicate your medication
  • are taking amiodarone or lithium medication

Find out about treatment for underactive thyroid.

  • show glossary terms
Sample of blood
During a blood test, a sample of blood is taken from a vein using a needle, so it can be examined in a laboratory.
Thyroid gland
The thyroid gland in the throat makes hormones to help control growth and metabolism (the process that turns the food we eat into energy).

Last reviewed: 13/10/2011

Next review due: 13/10/2013

Comments

6 Comments

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Comments are personal views. Any information they give has not been checked and may not be accurate.

danigirl1989 said on 12 December 2011

Is there any other way in which to test for an under-active Thyroid, as I have a massive fear of both needles and blood. I was supposed to go for a blood test last year but I never went because my fear is that bad. I do have symptoms of as under-active Thyroid, but I am too afraid to have a blood test.

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Goldilocks said on 17 July 2011

Well done Carrickgirl for being persistant and convince doctor to give you medication with amazing results. It has given me the courage to do tbe same x wish me luck x i hope and pray i have the same excellent results

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carrickgirl said on 30 June 2011

if you have symptoms of a low thyroid but your GP says your blood work is normal, but your symptoms persist, ask your GP to consider treating you on your symptoms for a short time to see if anything changes. This is what i had to do, as i had all the symptoms and more, as i was very ill at the time, my GP agreed to treat me temporally (against her better judgement) but it worked!! i lost 12lbs in weight in four weeks, i eventually started to thaw out as i was freezing all the time, i had energy for the first time in years and the dry skin,hair, and eyes settled down also my mood lifted and i could enjoy life again.My GP was amazed, and told me she wouldn't normally have done that, but because i was persistant and also ill she did it, and thank God she did,not many would if your blood work is on the low side of normal they will say that's normal,end of story.So if you are like i was, be persistant you know your own body. Good luck.

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LouLah said on 10 May 2011

I recently had a thyroid test and was told that I was borderline underactive. I've been told to come back for another test within 6 to 8 weeks. I think 6 months is far too long to wait for another test. I think you should insist on a test much sooner. Don't take no for an answer. And if you don't get any joy from your doctor, go to another one. Take care.

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favred said on 18 February 2011

Hello 529803. I have under active thyroid. Had gland removed years ago. That was bad enough without having a kidney removed. I still have no energy but that is another story. Going back to what you asked. If you cant face that for another 6 months push because the quicker they start to treat you the quicker you will feel better. The thyroid controls so much its as important as your heart, Good Luck and let me know how you get on.

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User529803 said on 17 February 2011

Hi, I was diagnosed with cancer of the kidney last year after having my kidney removed in August 2010 i thought my energy levels would return to normal and they did for a short while! After putting 6 stone on within the last 6 months and energy levels flagging my gp sent me for a blood test, it has come back as a border line underactive thyroid, (at least i know whats causing the weight gain) does anybody know if these 2 things could be related? My GP is suggesting i wait another 6 months before repeating the blood test as it's border line, although i do have most of the symptoms should i be starting treatment sooner than this (not sure i can feel like this for another 6 months) or should i push to start treatment sooner???

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