In euthyroid sick syndrome, which statement best describes thyroid hormone levels?

In euthyroid sick syndrome, which statement best describes thyroid hormone levels?

• A. Serum levels of thyroid hormones are low in clinically euthyroid patients with nonthyroidal systemic illness
• B. Thyroid hormones are normal
• C. TSH is elevated with low T4
• D. Thyroid hormones are elevated

Answer: (A)

Non-thyroidal illness can alter thyroid hormone levels even when the thyroid gland is functioning normally. In euthyroid sick syndrome, the body’s response to acute or chronic systemic illness shifts thyroid hormone metabolism, so circulating hormones fall despite the patient being clinically euthyroid. The most common pattern is a low T3 due to reduced peripheral conversion of T4 to the active T3 and shifts in hormone transport and clearance. T4 can be normal or low, and TSH is typically normal or low rather than elevated. This means the thyroid axis isn’t the primary problem; illness-driven changes produce lower thyroid hormone levels. That’s why the statement describing low thyroid hormone levels in clinically euthyroid patients with nonthyroidal systemic illness best fits euthyroid sick syndrome.

Non-thyroidal illness can alter thyroid hormone levels even when the thyroid gland is functioning normally. In euthyroid sick syndrome, the body’s response to acute or chronic systemic illness shifts thyroid hormone metabolism, so circulating hormones fall despite the patient being clinically euthyroid. The most common pattern is a low T3 due to reduced peripheral conversion of T4 to the active T3 and shifts in hormone transport and clearance. T4 can be normal or low, and TSH is typically normal or low rather than elevated. This means the thyroid axis isn’t the primary problem; illness-driven changes produce lower thyroid hormone levels. That’s why the statement describing low thyroid hormone levels in clinically euthyroid patients with nonthyroidal systemic illness best fits euthyroid sick syndrome.