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Thyroid UK
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What tests for secondary or central hypothyroidism please?

I have a "normal" TSH of 3 something and a borderline low free T4 of 12 ish. Many people have mentioned central/secondary hypo as I have almost every hypo symptom. But what tests are needed to diagnose central? I can't did clear info on this online. Links appreciated please. Or anyone who has been diagnosed with central what tests were used please as considering having them privately

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Central hypothyroidism is suggested by the combination of low FT4 and low FT3 (not necessarily on the floor - but lower than desirable) along with a TSH that is either low, or at least not as elevated as would be expected for the actual FT4 and FT3 results.

Further tests often focus on the other pituitary hormones such as prolactin, follicle stimulating hormone, luteinising hormone, adrenocorticotropic hormone. If they too are low, then the next step could well be an MRI scan. The thought being that if the anterior pituitary - where all these are made - is not working properly, then several of them are likely also to be affected. However, it is possible for only TSH production to be impaired.




I see from your other post you may be coeliac or gluten intolerant

Highly likely with gut issues to have low vitamin D, folate, ferritin and/or B12

Essential to test these plus thyroid antibodies

Low vitamins can cause symptoms in own tight, but also badly affect thyroid

For full evaluation you ideally need TSH, FT4, FT3, TT4, TPO and TG antibodies, plus vitamin D, folate, ferritin and B12 tested

See if you can get full thyroid and vitamin testing from GP. Unlikely to get FT3

Private tests are available


Medichecks Thyroid plus ultra vitamin or Blue Horizon Thyroid plus eleven are the most popular choice. DIY finger prick test or option to pay extra for private blood draw. Both companies often have money off offers.

All thyroid tests should be done as early as possible in morning and fasting. This gives highest TSH, lowest FT4 and most consistent results

Link about antibodies


Link about thyroid blood tests


Print this list of symptoms off, tick all that apply and take to GP


Also a TSH of 3 suggests thyroid is struggling. As you say it's important to see where both FT4 and FT3 are, not just TSH

Here is graph showing distribution of population TSH results.

Median TSH graph


TSH daily variation - illustrates why early morning testing is good idea


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Unless I'm misunderstanding the daily variation graph it looks as though the TSH is lowest at 1pm.


You want it at its HIGHEST to get diagnosed (or not have dose reduced)

Highest is midnight to 3am but obviously not practical to test then

Early as possible in morning is next best option.

TSH also drops after eating - hence advice to fast before test


Of course, I'm really not thinking properly - blame it on my 'morning miasma' and a poor night's sleep. I think I was getting mixed up with FT4 which needs to be at the lowest when testing. But even that seems confusing.

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Yes for lowest FT4 don't take Levo in 24 hours prior to test (T3 12 hours )


It’s a myth that TSH can’t be elevated in central Hypothyroidism. Having piled through countless peer reviewed scientific papers lately on the subject:

TSH can be inappropriately low, normal, or even slightly elevated (leading to misdiagnosis of primary Hypothyroidism and hence under-treatment), in presence of low or low-normal T4. The point is that the signal to the thyroid is absent or not working properly, as a result of either a dysfunction in the hypothalamus and/or pituitary.

The most common genetic cause of central Hypothyroidism was confirmed only in 2012 with a lengthy article in Endocrinology journal just this year. It went over a study that showed how while the TSH can rise with dropping T4 in a central Hypothyroidism state, it does not rise as much as it would in a normal person, hence signal is impaired.

Just this year Nature journal, most cited scientific journal in the world, published a lengthy article titled Central Hypothyroidism: a Neglected Disorder. Actually up to 90% of people with it are most likely still undiagnosed. Also I read some other stuff from leading Endocrinology journals in the world where it showed how T4 in the lower quarter or tertile of the range does not necessarily mean less severe symptoms than T4 below the range, the severity of symptoms can be the same. This is because every individual is different with their own set point and hence range.

There is such a gap between practice and the science it’s ridiculous. I’ve had doctors ignore my sources, leading peer reviewed science, which is like some dark age shit. They’d have no jobs without those who advanced the field then they laugh at them. But I do suggest using these sources to convince your doctor to best treat you.


I gave up with endocrinologists after 40 years of symptoms, then a diagnosis of a pituitary adenoma4 years ago. I resorted to self-medicating, with considerable help from the wonderful folks on this forum, which has improved my life considerably!


Low free T3 as well (and possibly an MRI or CT scan if there's a possibility of pituitary damage) the old TRH test will show if it is secondary or central (but GP and endo probably won't care which it is)

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Thyroid releasing hormone stimulation test - used to be THE test for hypo before TSH became dirt cheap. verywell.com/trh-stimulatio...

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