Professional and Linguistic Assessments Board (PLAB) Practice Exam

Which of the following laboratory results is associated with subacute thyroiditis?

1. High T4, low TSH with decreased uptake

2. Normal T4 and TSH

3. Low T4, high TSH with increased uptake

4. Very high T4 and normal TSH

The correct answer is: High T4, low TSH with decreased uptake

Subacute thyroiditis, often associated with viral infections, typically presents with a transient hyperthyroid state followed by a resolution phase. The correct laboratory results linked to this condition include a high level of thyroxine (T4) and low levels of thyroid-stimulating hormone (TSH) along with decreased radioactive iodine uptake. In subacute thyroiditis, inflammation of the thyroid gland leads to the release of stored thyroid hormones into the bloodstream, causing hyperthyroidism. The feedback mechanism responds by suppressing TSH production due to the elevated T4 levels. The decreased uptake in this scenario indicates that the thyroid gland is not producing more hormones in response to TSH due to the ongoing inflammation and damage to the glandular tissue. This combination of high T4 and low TSH with decreased uptake distinctly characterizes the phase of thyroiditis, differentiating it from other thyroid disorders where the uptake patterns differ, and it helps guide appropriate management of the condition. Understanding these results is crucial for diagnosing subacute thyroiditis versus other forms of thyroid dysfunction.