Causes for Decreased Thyroxine or Free Thyroxine Values

• Lab error

• Primary hypothyroidism

• Severe nonthyroid illness; * many patients

• Lithium therapy; some patients

• Severe TBG decrease (congenital, disease or drug induced) or severe albumin decrease*

• Dilantin, Depakene, or high dose salicylate drug

• Pituitary insufficiency

• Large doses of inorganic iodide (e.g., SSKI)

• Moderate or severe iodine deficiency

• Cushingís syndrome

• High-dose glucocorticoid drugs; some patients

• Pregnancy, third trimester (low-normal or small decrease)

• Addisonís disease; some patients (30%)

• Desipramine or amiodarone drugs; some patients

• Acute pyschiatric illness; a few patients

* FT4 less affected than T4

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