All of the following abnormalities might be expected in a severely ill patient EXCEPT

All of the following abnormalities might be expected in a severely ill patient EXCEPT

• A. Low rT3
• B. Low T4
• C. Low T3
• D. Low TSH

Answer: (A)

In severely ill patients, the thyroid axis often shows non-thyroidal illness (euthyroid sick) syndrome. The body alters thyroid hormone metabolism during illness, lowering the active hormone T3 by reducing its peripheral production from T4. T4 levels can drop as well, and the pituitary response (TSH) is often suppressed or remains normal rather than elevated. At the same time, the pathway shifts away from T3 production toward the inactive metabolite reverse T3, so reverse T3 levels tend to rise. Thus, you would expect low T3, possibly low T4, and low or normal TSH, with an increase in reverse T3. The abnormality that would not fit this pattern is a low reverse T3, since reverse T3 is typically elevated in severe illness rather than decreased.

In severely ill patients, the thyroid axis often shows non-thyroidal illness (euthyroid sick) syndrome. The body alters thyroid hormone metabolism during illness, lowering the active hormone T3 by reducing its peripheral production from T4. T4 levels can drop as well, and the pituitary response (TSH) is often suppressed or remains normal rather than elevated. At the same time, the pathway shifts away from T3 production toward the inactive metabolite reverse T3, so reverse T3 levels tend to rise.

Thus, you would expect low T3, possibly low T4, and low or normal TSH, with an increase in reverse T3. The abnormality that would not fit this pattern is a low reverse T3, since reverse T3 is typically elevated in severe illness rather than decreased.