Which of the following combinations of free thyroxine (FT4) level and thyroid-stimulating hormone (TSH) level is MOST likely in a patient with subclinical hypothyroidism?
About 5% of patients older than 65 years have hypothyroidism. Primary hypothyroidism is due to thyroid gland dysfunction, while secondary hypothyroidism is due to pituitary dysfunction. In primary hypothyroidism, thyroid-stimulating hormone (TSH) is increased due to a negative feedback loop that stimulates the failing gland, while free thyroxine (FT4) is low or low-normal. Low levels of both FT4 and TSH suggest secondary hypothyroidism, often associated with pituitary dysfunction. High FT4 levels with low TSH levels suggest primary hyperthyroidism (Figure).
Subclinical hypothyroidism is characterized by normal FT4 and high TSH. High TSH ranges from 5 to 15 mU/L, while normal TSH ranges from 0.3 to 4.5 mU/L. Generally, subclinical hypothyroidism is thought to have little or no perioperative significance. An increasing TSH level is the...
