**Core Concept**
Primary hypothyroidism is a condition where the thyroid gland fails to produce sufficient thyroid hormones (T3 and T4) due to a problem with the gland itself. This can be caused by various factors, including thyroiditis, thyroid surgery, or autoimmune diseases such as Hashimoto's thyroiditis.

**Why the Correct Answer is Right**
In primary hypothyroidism, the thyroid gland is unable to produce sufficient thyroid-stimulating hormone (TSH) receptor-binding proteins, leading to decreased production of T3 and T4. The decreased levels of T3 and T4 in the blood lead to an increase in TSH production by the pituitary gland, as it attempts to stimulate the thyroid gland to produce more hormones. The elevated levels of TSH are a hallmark of primary hypothyroidism and can be used to diagnose the condition.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe a finding in primary hypothyroidism.
* **Option B:** This option is incorrect because it is a characteristic of secondary hypothyroidism, not primary hypothyroidism.
* **Option C:** This option is incorrect because it describes a characteristic of thyroid hormone resistance, not primary hypothyroidism.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that primary hypothyroidism is characterized by an elevated TSH level, which is often the first sign of the condition. This can be used to differentiate it from secondary hypothyroidism, where the TSH level is low or normal.

**Correct Answer: D. Elevated TSH level.**