Reverse T3

[MissT]

Hello,

As a patient on levothyroxine and still exhibiting major symptoms of hypothyroidism (despite so-called 'normal' TSH), I would like to know why it is so difficult to get a Reverse T3 (RT3) blood test?

Also, if someone is not converting their synthetic T4 to T3 properly, why is it that some NHS doctors will prescribe T3, yet others refuse point blank?

[Dr Graham Beastall]

When I started measuring thyroid hormones in my laboratory 35 years ago I established an assay for reverse T3 (rT3). Several other laboratories did the same. The assay helped us a little in understanding the cause and time course of non-thyroidal illness but as experience of the assay grew there was a realisation that rT3 assays have nothing to contribute to the diagnosis or management of thyroid disease. Therefore, rT3 assays were universally regarded as of no value and virtually everyone stopped performing them. Today I am not aware of any NHS centre that offers a routine rT3 assay - and the UK is not unique in this respect. I am aware that some private laboratories offer rT3 assays (for a high fee) but I repeat that the results have no proven clinical value.

I hear a lot about reduced peripheral conversion of T4 into T3. Usually, there is no evidence to support this claim - it is often a diagnosis of exclusion in someone who has the symptoms of hypothyroidism but normal thyroid function tests. As I have explained elsewhere in this forum there can be subtle alterations in the metabolism of T4 in subjects who have a non-thyroidal illness. See Chapter 5b of The Thyroid Manager (http://www.thyroidmanager.org) for a full description. This article explains that there is not convincing evidence of the value of T3 replacement in patients with non-thyroidal illness and this is why most doctors are unwilling to give it. However, a few doctors will consider a carefully controlled trial of T3 in some patients as a pragmatic rather than an evidence based treatrment.