**Question:** A 20 year old young girl, presents with history of rapidly developing hirsutism and amenorrhea with change in voice. To establish a diagnosis you would like to proceed with which of the following tests in blood:

A. Testosterone
B. LH (Luteinizing Hormone)
C. FSH (Follicle-Stimulating Hormone)
D. Prolactin

**Correct Answer:** **D. Prolactin**

**Core Concept:** Rapidly developing hirsutism, amenorrhea, and a change in voice in a young female are clinical manifestations of hyperprolactinemia.

**Why the Correct Answer is Right:**

1. Prolactin (PRL) is a hormone produced by the anterior pituitary gland, which plays a crucial role in breast development, lactation, and regulation of menstrual cycles.
2. In females, a high prolactin level can lead to irregular menses, amenorrhea, and hirsutism due to suppression of gonadotropin-releasing hormone (GnRH) secretion, causing decreased LH and FSH production.
3. Elevated prolactin levels can also cause a change in voice due to the influence on the laryngeal and pharyngeal muscles.

**Why Each Wrong Option is Incorrect:**

1. Testosterone is a steroid hormone produced in the ovaries and testes, and is responsible for the development of secondary sexual characteristics in both males and females. It is not related to the clinical manifestations mentioned.
2. LH (Luteinizing Hormone) and FSH (Follicle-Stimulating Hormone) are both produced by the anterior pituitary gland and play a critical role in regulating menstrual cycles, spermatogenesis, and Leydig cell function. However, their elevation is more likely in cases of hypothalamic-pituitary-ovarian axis dysfunction (e.g., in polycystic ovary syndrome).
3. Prolactin is the correct hormone to be elevated in the given scenario, as it is responsible for the clinical manifestations described.

**Clinical Pearl:**

Understanding the role of prolactin in the context of the clinical presentation of a young female patient can help guide the diagnosis and management strategies for various endocrine disorders, such as idiopathic hirsutism, amenorrhea, and change in voice. An elevated prolactin level should prompt further investigation for the underlying cause, such as pituitary tumors, medications, or hypothyroidism, and appropriate management according to the identified cause.