This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diseases of Thyroid, Subject name: Medicine
What is the most common presentation of sick euthyoid state? 
Select and explain. 
A. Low T3 with normal T4, B. Low T3 with low T4, C. Low T3 with high T4, D. High T3 with high T4
A: Low T3 with normal T4
Answer: A: Low T3 with normal T4 
Explanation: The most common hormone pattern in sick Euthyroid syndrome is a decrease in total and free 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 deiodination is impaired, leading to increased reverse T3 (rT3). It is generally assumed that this low T3 state is adaptive, because it can be induced in normal individuals by fasting.