**Question:** In a patient of primary hypothyroidism, the hormonal profile will read -

A. Low T3
B. High TSH
C. Normal T4 level
D. High T3 and normal T4 levels

**Core Concept:**
Hypothyroidism is a condition in which the thyroid gland does not produce enough thyroid hormones. The main hormones produced by the thyroid gland are triiodothyronine (T3), thyroxine (T4), and thyroid-stimulating hormone (TSH). T3 and T4 are the active thyroid hormones, while TSH is produced by the pituitary gland in response to decreased thyroid hormone levels.

**Why the Correct Answer is Right:**
In primary hypothyroidism, the primary cause of low thyroid hormone production is usually due to an autoimmune disease (Hashimoto's thyroiditis) or damage to the thyroid gland. Consequently, the thyroid gland produces less T3 and T4, leading to a decrease in the amount of these hormones in the blood.

On the other hand, the pituitary gland responds to the decreased thyroid hormone levels by increasing TSH production. As a result, the hormonal profile in primary hypothyroidism will show low T3, high TSH, and normal T4 levels.

**Why Each Wrong Option is Incorrect:**

A. Low T3 is the correct choice because the primary goal of the question is to identify the hormonal profile in a patient with hypothyroidism.

B. High TSH is the correct choice because the pituitary gland is compensating for the decreased thyroid hormone production by producing more TSH.

C. Normal T4 level is incorrect because, as mentioned earlier, primary hypothyroidism results in decreased T4 production.

D. High T3 and normal T4 levels is incorrect because, as discussed, primary hypothyroidism results in decreased T3 and T4 production, not increased levels.

**Clinical Pearl:**
Primary hypothyroidism is a common endocrine disorder often caused by Hashimoto's thyroiditis, which leads to a cascade of events involving T3, T4, and TSH production. A detailed hormonal profile in hypothyroidism helps in diagnosing the condition and initiating appropriate treatment.