Reverse T3 (rT3), Triiodothyronine, Reverse

To distinguish low T3 "sick thyroid " пїЅ patients (usually increased) from true hypothyroidism

Interpretation

Increased In

Severe nonthyroidal illness except in some liver disorders, HIV, renal failure

Usually in hyperthyroidism and increased serum TBG

Decreased In

Often in hypothyroidism but overlaps with normal range

Limitations

Measurement is occasionally useful in hospitalized patients to distinguish between nonthyroidal illness and central hypothyroidism. Values are lower in central hypothyroidism, because of low production of T4. In patients with mild hypothyroidism, rT3 levels may be normal or even slightly higher limiting its usefulness.