**Core Concept**
Hyperandrogenism in a young woman, characterized by hirsutism, amenorrhea, and voice change, suggests an excess of androgens. This presentation is often seen in disorders of androgen excess, such as congenital adrenal hyperplasia, polycystic ovary syndrome (PCOS), or androgen-secreting tumors.

**Why the Correct Answer is Right**
Measuring testosterone levels is crucial to establish the diagnosis of hyperandrogenism. Testosterone is a key androgen responsible for the development of male secondary sexual characteristics, including hirsutism, deepening of the voice, and amenorrhea. Elevated testosterone levels can be seen in various conditions, including androgen-secreting tumors, congenital adrenal hyperplasia, and PCOS. A high testosterone level can guide further investigation and management.

**Why Each Wrong Option is Incorrect**
**Option A:** 17-OH progesterone is a useful marker for diagnosing congenital adrenal hyperplasia (CAH), specifically 21-hydroxylase deficiency, which can cause hyperandrogenism. However, it is not the first-line test in this scenario, as testosterone levels are more directly related to the patient's symptoms.

**Option B:** DHEA (dehydroepiandrosterone) is an androgen produced by the adrenal glands, but its levels are typically not elevated in cases of hyperandrogenism in women. DHEA is more relevant in the context of adrenal incidentalomas or Cushing's syndrome.

**Option D:** Estimating LH and FSH levels can be helpful in diagnosing PCOS, as these hormones are often elevated in women with this condition. However, LH/FSH ratios are more useful than individual hormone levels in this context.

**Clinical Pearl / High-Yield Fact**
In cases of suspected hyperandrogenism, always measure testosterone levels first, as they are the most direct indicator of androgen excess. Elevated testosterone levels can guide further investigation and management, including imaging studies, hormonal evaluation, and consideration of androgen-secreting tumors.

**✓ Correct Answer: C. Testosterone**