Serum free triiodothyronine (T3) to free thyroxine (T4) ratio in treated central hypothyroidism compared with primary hypothyroidism and euthyroidism | Endocrinología y Nutrición (English Edition)

Article information

Abstract

The standard treatment of hypothyroidism (central and primary) consists of thyroxine (T4) administration alone. However, the normal thyroid gland produces a small proportion of triiodothyronine (T3) directly into the circulation.

Aim

We aimed to study the free T3 to free T4 ratio in treated central hypothyroidism compared with euthyroidism and treated primary hypothyroidism.

Methods

Eighty-three subjects were included in this cross-sectional study: 36 with central hypothyroidism, 20 with primary hypothyroidism and 27 healthy controls. A clinical history and a physical examination, including height and weight measurement, were performed and body mass index (BMI) was calculated. Fasting blood was drawn to measure T3, T4, free T3, free T4 and TSH.

Results

The free T3 to free T4 ratio was lower in treated central hypothyroidism than in euthyroidism but was similar to treated primary hypothyroidism. Free T4 was higher in treated central and primary hypothyroidism than in euthyroidism. Age, sex and BMI did not affect the free T3 to free T4 ratio.

Conclusions

Treated patients with central hypothyroidism had a lower free T3 to free T4 ratio, similar free T3 levels and higher free T4 concentrations than euthyroid controls, whereas all these parameters were similar in central and primary hypothyroid patients treated with T4. The question of whether these findings translate into adequate tissue concentrations of free thyroid hormones in all tissues remains to be answered. Further studies should aim to determine whether clinical outcomes could be improved by a treatment achieving more physiological plasma concentrations.

Keywords:

Central hypothyroidism

Triiodothyronine to thyroxine ratio

Resumen

El tratamiento habitual del hipotiroidismo (central y primario) consiste en administrar sólo tiroxina (T4). Sin embargo, la glándula tiroides normal produce una proporción pequeña de triyodotironina (T3) que va directamente a la circulación.

Objetivo

Estudiar la razón entre las concentraciones de T3 /T4 circulantes en el hipotiroidismo central tratado respecto al eutiroidismo y al hipotiroidismo primario también tratado.

Métodos

Se incluyeron 83 sujetos en este estudio transversal: 36 presentaban hipotiroidismo central, 20 hipotiroidismo primario y 27 eran controles sanos. Se realizó una historia clínica y una exploración física que incluía la altura y el peso, y se calculó el índice de masa corporal (IMC). Se extrajo sangre en ayunas para medir T3, T4, T3 libre, T4 libre y TSH.

Resultados

La razón T3/T4 circulantes fue inferior en el hipotiroidismo central que en el eutiroidismo, pero similar a la del hipotiroidismo primario. La T4 libre fue mayor en el hipotiroidismo central y en el primario que en el eutiroidismo. La edad, el sexo y el IMC no afectaron la razón T3 /T4 circulante.

Conclusiones

Los pacientes con hipotiroidismo central tratados presentan una razón T3/T4 circulante más baja, niveles de T3 circulante similares y concentraciones de T4 libre superiores a los controles eutiroideos; sin embargo, todos estos parámetros son similares en los pacientes con hipotiroidismo central y primario tratados con T4. No se sabe si esto se traduce en concentraciones tisulares adecuadas de hormonas tiroideas libres en todos los tejidos. Queda por investigar si un tratamiento que obtenga una concentración plasmática más fisiológica sería mejor desde el punto de vista de los resultados clínicos. Es de esperar que se diseñen estudios en esa dirección.

Palabras clave:

Hipotiroidismo central

Razón triyodotironina tiroxina

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