The physician orders laboratory tests to confirm hyperthyroidism in a female client with classic signs and symptoms of this disorder. Which test result would confirm the diagnosis?
A. No increase in the thyroid-stimulating hormone (TSH) level after 30 minutes during the TSH stimulation test.
B. A decreased TSH level.
C. An increase in the TSH level after 30 minutes during the TSH stimulation test.
D. Below-normal levels of serum triiodothyronine (T3) and serum thyroxine (T4) as detected by radioimmunoassay.
Correct Answer: A. No increase in the thyroid-stimulating hormone (TSH) level after 30 minutes during the TSH stimulation test
In the TSH test, failure of the TSH level to rise after 30 minutes confirms hyperthyroidism.
Option B: A decreased TSH level indicates a pituitary deficiency of this hormone.
Option C: If the TSH level rises after 30 minutes, then the client has no hyperthyroidism.
Option D: Below-normal levels of T3 and T4, as detected by radioimmunoassay, signal hypothyroidism. A below-normal T4 level also occurs in malnutrition and liver disease and may result from the administration of phenytoin and certain other drugs.