Version July 2025
| Binding protein abnormalities |
| TBG deficiency |
| Hereditary (rare) – Mutations in TBG gene, X-linked recessive |
| Acquired |
| Androgens (including testosterone, anabolic steroids) |
| Other drugs (danazol, glucocorticoids, L-asparaginase, niacin) |
| Nephrotic syndrome |
| Cushing syndrome |
| Acromegaly |
| Decreased T4 binding to TBG |
| Furosemide |
| Heparin* |
| Salicylates |
| Salsalate |
| Some NSAIDs (eg, fenclofenac, mefenamic acid) |
| Increased T4 metabolism or clearance |
| Antiseizure medications (phenytoin, carbamazepine, phenobarbital) |
| Oral T3 administration |
NSAIDs: nonsteroidal antiinflammatory drugs; T3: triiodothyronine; T4: thyroxine; TBG: thyroxine-binding globulin.
* Total T4 may be reduced, and free T4 may be increased.