In a client with primary hypothyroidism, which lab value is likely to be elevated?

In a client with primary hypothyroidism, the thyroid-stimulating hormone (TSH) is likely to be elevated due to the body's feedback mechanism. In primary hypothyroidism, the thyroid gland is underactive and does not produce adequate levels of thyroid hormones (such as T3 and T4). As a result, the pituitary gland responds to the low levels of circulating thyroid hormones by producing more TSH to stimulate the thyroid gland. This leads to an elevated level of TSH in the blood.

The measurement of TSH is crucial in diagnosing and managing hypothyroidism because it reflects the pituitary's response to the low thyroid hormone production and serves as an indicator of thyroid function. In contrast, free T4, serum T4, and serum T3 levels typically remain low in primary hypothyroidism, as the impaired thyroid function leads to decreased production of these hormones.

Therefore, the elevation of TSH in this context is a classic laboratory finding associated with primary hypothyroidism, reinforcing the role of TSH as a regulatory hormone in the thyroid axis.