thyroxine [T4] (total) in serum

Reference interval

• Adult male: 4.6-10.5 ug/dL
• Adult female: 5.5-11.0 ug/dL
• 5.0-10.7 ug/dL, age > 60 years

Increases

• hyperthyroidism
• euthyroid hyperthyroxinemia
  • increased thyroid-binding globulin (TBG) caused by:
    • estrogens
      • pregnancy
    • hepatitis
    • porphyria
    • biliary cirrhosis
  • familial dysalbuminemia
  • increased T4 binding to transthyretin
  • anti T4 antibodies

Decreases

• hypothyroidism
• euthyroid hypothyroxinemia: (decreased thyroid-binding globulin)
  • androgens
  • glucocorticoids
  • nephrotic syndrome
  • systemic illness

Methods

• immunoassay

Specimen

• serum, refrigerate immediately, stable for 7 days at room temp, but storage at 4 C preferred.

More general terms

• thyroxine [T4] (total) in body fluid
• thyroid function test

More specific terms

• thyroxine [T4] (albumin-bound) in serum
• thyroxine [T4] (prealbumin-bound) in serum
• thyroxine [T4] (thyroxine-binding globulin-bound) in serum

Additional terms

• free thyroxine index (fT4I)
• thyroxine (T4)
• thyroxine [T4] (free) in serum

Component of

• thyroxine (T4)/thyroxine-binding globulin (TBG) in serum/plasma
• thyroid panel
• triiodothyronine (T3)/thyroxine (T4) in serum/plasma