1. Which of the following statements about the hypothalamic–pituitary–thyroid axis is not correct?
A. Thyroid-stimulating hormone (TSH) stimulates the thyroid to produce the thyroid hormones T3 and T4.
B. Thyroid-releasing hormone (TRH) from the hypothalamus stimulates the pituitary to produce TSH.
C. The primary negative feedback to the hypothalamus and to the pituitary is from T4, with less negative feedback from T3.
D. T4 is made in much greater quantities within the thyroid than T3.
The correct answer is C. The primary negative feedback to the hypothalamus and to the pituitary is from T3. All of the other statements about the thyroid axis are correct.
2. Which of the following tests is the most sensitive first-line screening test for suspected thyroid abnormalities?
D. Thyroid-releasing hormone (TRH)
The correct answer is A. If the TSH is within the reference range, no further testing is performed. However, if the TSH is outside the reference range, a free T4 measurement is typically performed.
3. Which of the following statements is not true about thyroid hormone measurements?
A. Changes in serum thyroid hormone-binding protein concentrations may affect total T4 and T3 concentrations.
B. An assessment for free T4, which represents >0.1% of the total T4, is more helpful in evaluating thyroid function because it is not affected by changes in the amounts of thyroid hormone-binding protein.
C. The concentrations of thyroid hormone-binding proteins also influence the total T3 level.
D. The T3 concentration has similarly important diagnostic value in the assessment of both hyperthyroidism and hypothyroidism.
The correct answer is D. In hyperthyroidism, the concentrations of total T3 and total T4 correlate in the vast majority of patients. However, measurement of T3 concentration is of limited diagnostic value in the assessment of hypothyroidism.
4. Antithyroid antibodies are relatively common. They are present in approximately 15% of the general population, and responsible for much of the thyroid disease in societies that ingest adequate amounts of iodine. Which one of the following antibodies affects the thyroid?
A. Antitopoisomerase antibodies
B. Antimicrosomal/Antithyroid peroxidase antibodies (anti-TPO)