What laboratory test results would be expected for a patient who has not taken levothyroxine as prescribed and shows symptoms of hypothyroidism?

In a patient who has not taken levothyroxine as prescribed and shows symptoms of hypothyroidism, the expected laboratory test results would indeed show a decreased T4 level and an increased TSH level.

This physiological response is grounded in the feedback mechanism of the hypothalamic-pituitary-thyroid axis. In hypothyroidism, the thyroid gland is not producing adequate amounts of thyroid hormones (T3 and T4) to meet the body's needs. As a result, the concentration of T4 in the bloodstream decreases. In response to low levels of circulating T4, the anterior pituitary gland secretes higher levels of thyroid-stimulating hormone (TSH) to stimulate the thyroid gland to produce more thyroid hormones. Therefore, an increase in TSH with a concurrent decrease in T4 is indicative of hypothyroidism, especially in the context of non-compliance with levothyroxine treatment.

This understanding of the hormonal feedback loop is crucial in diagnosing and managing thyroid disorders, and it clarifies why decreased T4 and increased TSH align with the symptoms and the scenario described.