Decreased T3

Abnormally low serum triiodothyronine (T3) concentration (total 80–200 ng/dL or free 2.3–4.1 pg/mL), reflecting reduced thyroid hormone activity.

Causes

• Primary hypothyroidism

  • Hashimoto's disease

  • Prior thyroid surgery

  • Radiation therapy

• Central hypothyroidism

• Nonthyroidal illness syndrome (euthyroid sick syndrome)

  • Severe illness

  • Trauma

  • Infections

• Medications

  • Corticosteroids

  • β-blockers

  • Amiodarone

• Malnutrition

• Impaired conversion of T4 to T3

  • Liver failure

  • Kidney failure