A 5–year old boy presents with pubic hair development. He is tall and has increased pigmentation of his genitalia and phallic enlargement. Blood pressure is 130/90 mm g. Measurement of which of the following diagnostic? hormones would be most likely to be diagnostic?
**Core Concept**
The boy's presentation is consistent with precocious puberty, a condition where pubertal changes occur before the age of 8 in boys. This condition can be caused by various factors, including congenital adrenal hyperplasia or tumors that secrete sex hormones. The key to diagnosing the underlying cause is identifying the hormone responsible for the precocious puberty.
**Why the Correct Answer is Right**
The boy's symptoms, such as pubic hair development, increased pigmentation of his genitalia, and phallic enlargement, suggest an excess of androgens. The correct answer, **Testosterone**, is a key androgen that regulates male secondary sexual characteristics. Elevated levels of testosterone would be diagnostic of androgen secretion, which could be due to various causes such as congenital adrenal hyperplasia, tumors, or exogenous administration.
**Why Each Wrong Option is Incorrect**
* **Option A:** Luteinizing hormone (LH) is a hormone that stimulates the testes to produce testosterone, but measuring LH would not diagnose the underlying cause of precocious puberty. Elevated LH levels would indicate testicular dysfunction rather than androgen secretion.
* **Option B:** Follicle-stimulating hormone (FSH) is another hormone that regulates testicular function, but like LH, it would not be diagnostic of androgen secretion.
* **Option C:** Dehydroepiandrosterone sulfate (DHEAS) is a precursor to androgens, but measuring DHEAS would not be diagnostic of androgen secretion in this context.
**Clinical Pearl / High-Yield Fact**
In cases of precocious puberty, it's essential to identify the underlying cause to prevent long-term consequences such as short stature or infertility. Measuring androgen levels, such as testosterone, is a critical step in diagnosing the condition.
**Correct Answer:** C. Testosterone