Non-Thyroidal Illness (NTI)

Already a few hours after the onset of acute illness, marked changes in serum thyroid hormone levels occur. This is referred to as non-thyroidal illness (NTI) also known as the low T3 syndrome and the euthyroid sick syndrome. The most characteristic and persistent abnormality is a low serum T3. Nevertheless, patients usually have no clinical signs of thyroid dysfunction. A low T3 in euthyroid patients is also seen during caloric deprivation. Both in NTI and in fasting there is a negative energy balance in the majority of cases. Therefore, the low levels of T3 during NTI and starvation have been interpreted as an attempt to save energy expenditure, which does not need intervention. However, this remains controversial and has been a debate for many years.