**Core Concept**
Hyperprolactinemia is a condition characterized by elevated levels of prolactin, a hormone produced by the pituitary gland. Prolactin plays a crucial role in lactation, reproductive functions, and other physiological processes. The diagnosis of hyperprolactinemia is typically based on laboratory measurements of prolactin levels.

**Why the Correct Answer is Right**
Hyperprolactinemia is generally defined as a prolactin level above 200 ng/mL (nanograms per milliliter) in non-pregnant, non-lactating women and men. This threshold helps distinguish between normal physiological fluctuations and pathological conditions that may cause elevated prolactin levels. The pituitary gland's dopamine-producing neurons regulate prolactin secretion, and disruptions in this feedback loop can lead to hyperprolactinemia.

**Why Each Wrong Option is Incorrect**
**Option A:** 50 ng/mL is considered a normal prolactin level in non-pregnant, non-lactating individuals, and values below 200 ng/mL are not indicative of hyperprolactinemia.

**Option B:** 100 ng/mL is still within the normal range for most individuals, and levels below 200 ng/mL are not typically associated with hyperprolactinemia.

**Option C:** 150 ng/mL is also within the normal range, and values below 200 ng/mL are not sufficient to diagnose hyperprolactinemia.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that hyperprolactinemia can be caused by various factors, including pituitary tumors, thyroid disorders, and certain medications. A thorough evaluation, including laboratory tests and imaging studies, is necessary to determine the underlying cause of elevated prolactin levels.

**✓ Correct Answer: D. 200**