Explain sick euthyroid syndrome and how to approach thyroid function testing during acute illness and critical illness.

Explain sick euthyroid syndrome and how to approach thyroid function testing during acute illness and critical illness.

• A. In acute illness, T3 increases and TSH rises dramatically.
• B. In acute illness, T3 decreases (and sometimes T4), TSH may be normal or low; reflects illness rather than primary thyroid disease; test after recovery and treat underlying illness.
• C. Thyroid function is always normal during acute illness and requires no testing.
• D. Treat hypothyroidism aggressively during acute illness to normalize TSH.

Answer: (B)

During acute or critical illness, thyroid test results can change even when the thyroid itself is normal. This pattern is called sick euthyroid syndrome. The body’s response to illness includes lowering the conversion of T4 to the active T3 in peripheral tissues, which causes T3 levels to fall. Sometimes T4 can be low as well, and reverse T3 may rise. TSH is not reliably elevated—in fact it is often normal or low in severe illness. These changes reflect the illness state, not primary thyroid disease. Because of this, the best approach is to focus on treating the underlying illness and avoid diagnosing or treating presumed thyroid disease based on these test results alone during acute illness. Thyroid testing is typically deferred or reinterpreted after recovery; retesting TSH and free T4 once the patient has improved helps distinguish true hypothyroidism from the non-thyroidal illness effect. If thyroid function abnormalities persist after recovery, or if there is a clear history or evidence of true thyroid disease, then a more thorough evaluation is warranted. In the meantime, avoid aggressive thyroid hormone therapy during acute illness unless there is a proven need.

During acute or critical illness, thyroid test results can change even when the thyroid itself is normal. This pattern is called sick euthyroid syndrome. The body’s response to illness includes lowering the conversion of T4 to the active T3 in peripheral tissues, which causes T3 levels to fall. Sometimes T4 can be low as well, and reverse T3 may rise. TSH is not reliably elevated—in fact it is often normal or low in severe illness. These changes reflect the illness state, not primary thyroid disease.

Because of this, the best approach is to focus on treating the underlying illness and avoid diagnosing or treating presumed thyroid disease based on these test results alone during acute illness. Thyroid testing is typically deferred or reinterpreted after recovery; retesting TSH and free T4 once the patient has improved helps distinguish true hypothyroidism from the non-thyroidal illness effect. If thyroid function abnormalities persist after recovery, or if there is a clear history or evidence of true thyroid disease, then a more thorough evaluation is warranted. In the meantime, avoid aggressive thyroid hormone therapy during acute illness unless there is a proven need.