Free triiodothyronine/free thyroxine ratio in children with congenital hypothyroidism

[helvella]

This paper appears to be of significance to anyone who has congenital hypothyroidism (CH) - and those involved with them. Although this paper is specifically about children, it would appear as well worth reading for adults.

We have seen levothyroxine monotherapy used for CH questioned here several times.

Four (out of 24) references are to papers by Midgley JEM ( @diogenes ), et al.. Which suggests that the messages of their work are being picked up, are being incorporated into papers, and will be guiding future research.

Free triiodothyronine/free thyroxine ratio in children with congenital hypothyroidism

in Endocrine Connections

Authors: Carmen Sydlik1, Ilja Dubinski2, Susanne Bechtold2, and Heinrich Schmidt2

DOI: doi.org/10.1530/EC-22-0032

Volume/Issue: Volume 11: Issue 7

Article ID: e220032

Article Type: Research Article

Online Publication Date: 14 Jul 2022

Abstract

Thyroid-stimulating hormone is generally regarded as a standard parameter for the evaluation of thyroid function. However, relying on this hormone alone can be misleading. Therefore, thyroxine/free-thyroxine levels are used in patients with levothyroxine substitution for the adjustment of therapy. Even with normal values for free thyroxine, decreased values for the free-triiodothyronine/free-thyroxine ratio have already been described in adults. In this study, the free-triiodothyronine/free-thyroxine ratio of 25 children with congenital hypothyroidism was compared with 470 healthy children seen for other reasons and then for thyroid dysfunction. Mean free thyroxine in congenital hypothyroidism was just below the upper limit of normal and significantly higher than in control group. Mean values for free triiodothyronine showed no significant difference between the two groups. The mean value for the free triiodothyronine/free-thyroxine ratio in control group was 3.23. Significantly lower ratios were found in the congenital hypothyroidism group with a mean value of 2.5, due to higher values for free thyroxine compared to free triiodothyronine. Furthermore, an increased free triiodothyronine/free-thyroxine ratio was found at higher thyroid-stimulating hormone values due to lower values for free thyroxine. In this study, we demonstrate that the free triiodothyronine/free-thyroxine ratio was significantly lower in children with congenital hypothyroidism compared to the control group. This is most likely due to the higher values for free thyroxine in this group compared to similar values for free triiodothyronine in both groups. Further studies with differentiated thyroid hormone therapy are needed in order to understand the role of peripheral euthyroidism.

Keywords: congenital hypothyroidism; free triiodothyronine; free thyroxine; levothyroxine

Full paper viewable online or downloadable as a PDF.

ec.bioscientifica.com/view/...

[jimh111]

I haven’t read this but isn’t the difference in ratios due to the patients being on levothyroxine monotherapy? If so, it seems the study was an awful waste of time.

[helvella Administrator Thyroid UK in reply to jimh111]

I think it was! At least in the sense of "Quelle surprise?"

Conclusion ends: In this context, the fT3/fT4 ratio as a treatment parameter for LT4 therapy and the role of supplementary LT3 therapy should also be further investigated.

I feel it quite incredible that we have reached around sixty years of levothyroxine, with it being used as monotherapy in CH for much of that time - and those deciding on the treatment and dose(s) are still calling for more research.

[jimh111 in reply to helvella]

… and who is being paid for this research. The recent NICE proposals for TSH suppression in thyroid cancer patients looked at over 1500 studies and only accepted one which they classified as ‘very poor. If this is so we should push for a 99% reduction in medical research budgets.

[helvella Administrator Thyroid UK in reply to jimh111]

This paper says:

Funding

This work did not receive any specific grant from any funding agency in the public, commercial, or not-for-profit sector.