Examkin

Question

Difficulty: EasyEndocrinology and Metabolism

Match each of the following thyroid function test (TFT) laboratory profiles with the most likely underlying pathophysiologic diagnosis.

  • Elevated TSH, decreased free T4Primary hypothyroidism
  • Decreased (suppressed) TSH, elevated free T4Primary hyperthyroidism
  • Elevated TSH, normal free T4Subclinical hypothyroidism
  • Decreased or inappropriately normal TSH, decreased free T4Central (secondary) hypothyroidism

Answer

Elevated TSH with decreased free T4 matches Primary hypothyroidism. Suppressed TSH with elevated free T4 matches Primary hyperthyroidism. Elevated TSH with normal free T4 matches Subclinical hypothyroidism. Decreased TSH with decreased free T4 matches Central (secondary) hypothyroidism.
The physiological relationship between TSH and free T4 operates on a strict negative feedback loop. Primary thyroid disorders present with TSH and free T4 moving in opposite directions because the intact pituitary is responding appropriately to abnormal peripheral hormone levels. Central disorders present with them moving in the same direction, as the pituitary/hypothalamus is the source of the defect.

Step-by-Step Solution

1
Analyze the free T4 level to determine the clinical state of thyroid function.
Categorizes the patient into a hyperthyroid, hypothyroid, or euthyroid clinical state.
Free T4 represents the biologically active thyroid hormone in circulation.
2
Analyze the TSH level in relation to the free T4 level.
Determines whether the expected hypothalamic-pituitary-thyroid negative feedback loop is intact or disrupted.
If TSH and free T4 move in opposite directions, the defect is primary (at the thyroid). If they move in the same direction or TSH fails to respond properly, the defect is central (at the pituitary or hypothalamus).

Key Concept

Interpretation of the hypothalamic-pituitary-thyroid axis via classic TSH and free T4 patterns.
Rate this question

Topics

Endocrinology and Metabolism

More questions from this topic