Most common presentation of sick euthyroid syndrome is?

Any acute, severe illness can cause abnormalities of circulating TSH or thyroid hormone levels in the absence of underlying thyroid disease, making these measurements potentially misleading. The major cause of these hormonal changes is the release of cytokines such as IL-6. This is called Sick Euthyroid Syndrome (Nonthyroidal illness).The most common hormone pattern in sick euthyroid syndrome (SES) is a decrease in total and unbound T3 levels (low T3 syndrome) with normal levels of T4 and TSH. The magnitude of the fall in T3 correlates with the severity of the illness.T4 conversion to T3 peripheral 5' (outer ring) deiodination is impaired, leading to increased reverse T3 (rT3). Since rT3 is metabolized by 5' deiodination, its clearance is also reduced. Thus, decreased clearance rather than increased production is the major basis for increased rT3. Reference : page 2299 Harrison's Principles of Internal Medicine 19th edition