Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1251 page)

   Familial dysalbuminemic hyperthyroxinemia—albumin binds T
₄
but not T
₃
more avidly than normal, causing changes similar to thyrotoxicosis (total T
₄
approximately 20 μg/dL, normal thyroid hormone–binding ratio, increased free T
₄
index), but the patient is not clinically thyrotoxic.

   Serum T
₄
>20 μg/dL usually indicates true hyperthyroidism rather than increased TBG.

   May be found in euthyroid patients with increased serum TBG.

   Much higher in first 2 months of life than in normal adults.

Decreased In

   Hypothyroidism

   Hypoproteinemia (e.g., nephrosis, cirrhosis)

   Certain drugs (phenytoin, triiodothyronine, testosterone, ACTH, corticosteroids)

   Euthyroid sick syndrome

   Decrease in TBG

Normal In

   Hyperthyroid patients with

   T
₃
thyrotoxicosis

   Factitious hyperthyroidism owing to T
₃
(Cytomel)

   Decreased binding capacity due to hypoproteinemia or ingestion of certain drugs (e.g., phenytoin, salicylates)