Thyroid Function Tests: Abnormal results

Elevated T₄ levels can be caused by:

• acute thyroiditis
• birth control pills
• clofibrate (Altromed-S)
• contrast x rays using iodine
• estrogen therapy
• heparin
• heroin
• hyperthyroidism
• pregnancy
• thyrotoxicosis
• toxic thyroid adenoma

Cirrhosis and severe non-thyroid disease can raise T₄ levels slightly.

Reduced T₄ levels can be caused by:

• anabolic steroids
• androgens
• antithyroid drugs
• cretinism
• hypothyroidism
• kidney failure
• lithium (Lithane, Lithonate)
• myxedema
• phenytoin
• propranolol

Although T₃ levels usually rise and fall when T₄ levels do, T₃ toxicosis causes T₃ levels to rise while T₄ levels remain normal. T₃ toxicosis is a complication of:

• Graves' disease
• toxic adenoma
• toxic nodular goiter

T₃ levels normally rise when a woman is pregnant or using birth-control pills. Elevated T₃ levels can also occur in patients who use estrogen or methadone or who have:

• certain genetic disorders that do not involve thyroid malfunction
• hyperthyroidism
• thyroiditis
• T₃ thyrotoxicosis
• toxic adenoma.

Low T₃ levels may be a symptom of:

• acute or chronic illness
• hypothyroidism
• kidney or liver disease
• starvation.

Decreased T₃ levels can also be caused by using:

• anabolic steroids
• androgens
• phenytoin
• propranolol
• reserpine (Serpasil)
• salicylates in high doses

TBG levels, normally high during pregnancy, are also high in newborns. Elevated TBG levels can also be symptoms of:

• acute hepatitis
• acute intermittent porphyria
• hypothyroidism
• inherited thyroid hormone abnormality

TBG levels can also become high by using:

• anabolic steroids
• birth control pills
• anti-thyroid agents
• clofibrate
• estrogen therapy
• phenytoin
• salicylates in high doses
• thiazides
• thyroid medications
• warfarin (Coumadin)

TBG levels can be raised or lowered by inherited liver disease whose cause is unknown.

Low TBG levels can be a symptom of:

• acromegaly
• acute hepatitis or other acute illness
• hyperthyroidism
• kidney disease
• malnutrition
• marked hypoproteinemia
• uncompensated acidosis

A high degree of resin uptake and high thyroxine levels indicate hyperthyroidism. A low degree of resin uptake, coupled with low thyroxine levels, is a symptom of hypothyroidism.

Thyroxine and triiodothyronine resin uptake that are not both high or low may be a symptom of a thyroxine-binding abnormality.

Long-acting thyroid stimulator, not usually found in blood, is present in the blood of 80% of patients with Graves' disease. It is a symptom of this disease whether or not symptoms of hyperthyroidism are detected.

— Maureen Haggerty