Low t3 syndromeE07.8

With normal or slightly decreased levels of TSH, fT3 (and fT4), patients complain of symptoms similar to those of hypothyroidism. The constellation is accompanied by relatively high reverse T3 (rT3) (rT3 competes with fT3 for the specific T3 receptor, but is almost ineffective (T3).

Low T3 syndrome is caused by a disturbance in the conversion of T4 to T3 (hypodeiodization). The increase in rT3 leads via a negative feedback loop to a reduced liberation of thyroid hormones, since the pituitary gland's release of TSH and the hypothalamic release of TRH (thyrotropin releasing hormone) is suppressed.

Low T3 syndrome occurs in patients suffering from "non thyroid" diseases. These include severe general diseases such as cirrhosis of the liver, diabetic ketoacidosis, anorexia, burns or sepsis (Hu YY et al. 2015). But also states of exhaustion, depression, mental and physical stress situations (operations, traumas).

Various drugs such as glucocorticosteroids, antiarrhythmic drugs, beta-receptor blockers or phenobarbiturates can also inhibit T4/T3 conversion as required.

It should be noted that low T3 syndrome can be associated with a reduced body temperature ("Wilson's Temperature Syndrome" - WTS).

Reduced fT3 level, normal or reduced levels of fT4 and TSH. Increased values of rT3 (Böhm BO 2018)

The patients are considered to be euthyroid. The usefulness of a substitution therapy is evaluated differently.

1. Böhm BO (2018) Thyroid hormones. In: Neumeister B et al. (Eds) Clinical guide to laboratory diagnostics. Elsevier GmbH S. 293-294
2. Hu YY et al(2015) Euthyroid sick syndrome in children with diabetic ketoacidosis. Saudi Med J 36:243-247.
3. Vardarli I et al(1987) The hypothalamo-hypophyseal thyroid axis, plasma protein concentrations and the hypophyseo-gonadal axis in low T3 syndrome following acute myocardial infarct. Clin week 65:129-133.