Final answer:
In primary clinical hypothyroidism, thyroid function tests reveal high TSH and low T3 and T4 levels, indicating a deficiency in thyroid hormone production due to the thyroid gland itself. A decrease in BMR and hypercholesterolemia are also common. Treatment usually involves thyroid hormone replacement therapy.
Step-by-step explanation:
In primary clinical hypothyroidism, thyroid function tests (TFTs) typically show elevated levels of thyroid-stimulating hormone (TSH) and low levels of thyroid hormones triiodothyronine (T3) and thyroxine (T4). This is reflective of a deficiency in thyroid hormone production by the thyroid gland itself. A high TSH level indicates that the pituitary gland is releasing more of this hormone in an attempt to stimulate the thyroid gland to produce more T3 and T4, but due to primary hypothyroidism, the thyroid is unable to respond adequately. Consequently, T3 and T4 levels drop, leading to various symptoms such as tiredness, weight gain, and cold intolerance. It is important to note that hypothyroidism - a lack of thyroid hormone production - leads to a decreased basal metabolic rate (BMR), which in turn can result in hypercholesterolemia (increased cholesterol levels). This condition requires thyroid hormone replacement therapy, usually in the form of levothyroxine, to mitigate these effects.