Thyroxine (T4) Serum Adult: 5-12 µg/dl Children: 10-20 years: 4.2-11.8 µg/dl 1-10 yearss: 6.4-15 µg/dl 2-10 months: 7.8-16.5 µg/dl Newborn: 6.4-23.2 µg/dl To evaluate thyroid function To confirm the diagnosis of hyper- or hypothyrodism To evaluate therapy for hyper- or Hypothyroidism Hyperthyroidism Acute or Subacute Thyroiditis Hypothyroidism Chronic or Subacute Thyroiditis Myxedema Cretinism Liver disorders Protein-wasting diseases such as chronic renal failure Medications (androgen, aspirin, chlorpropamide, estrogen, heparin, iodides, thyroid replacement medications, methadone, phenytoin, reserpine, steroids, sulfonamides, sulfonylureas, tolbutamide)