A 50-year-old man consults you because he has been having transient periods of rapid heart beat accompanied by sweating, flushing, and a sense of impending doom. Examination is unrevealing, with no evidence of arrhythmia at the time of the exam. However, the man’s wife is a nurse, so the physician asks that she take vital signs the next time one of the episodes occurs. She does, and demonstrates a BP of 195/140 with heart rate 160/min during the episode. She promptly brings him to you, but the spell is over by the time that he is seen. Urinary measurement of which of the following would most likely be diagnostic in this case?

**Core Concept**
The patient is experiencing episodes of hypertension and tachycardia, which are classic symptoms of a condition known as pheochromocytoma. This is a type of tumor that arises from the chromaffin cells of the adrenal medulla, leading to the excessive production of catecholamines such as epinephrine and norepinephrine.

**Why the Correct Answer is Right**
The excessive production of catecholamines in pheochromocytoma leads to increased levels of these hormones in the bloodstream. One of the key features of pheochromocytoma is the presence of elevated levels of metanephrines, which are the metabolites of catecholamines. Measuring the levels of metanephrines in the urine is a sensitive and specific test for diagnosing pheochromocytoma. This is because the tumor cells produce large amounts of catecholamines, which are then metabolized to metanephrines, leading to elevated levels in the urine.

**Why Each Wrong Option is Incorrect**
* **Option A:** Vanillylmandelic acid (VMA) is another metabolite of catecholamines, but it is not as sensitive or specific as metanephrines for diagnosing pheochromocytoma.
* **Option B:** Creatinine is a waste product that is produced by the kidneys and is not directly related to the diagnosis of pheochromocytoma.
* **Option D:** Uric acid is a waste product that is produced by the breakdown of DNA and is not directly related to the diagnosis of pheochromocytoma.

**Clinical Pearl / High-Yield Fact**
It's worth noting that pheochromocytomas are rare tumors, but they are often associated with other conditions such as multiple endocrine neoplasia (MEN) syndromes. A high index of suspicion and a thorough diagnostic workup are necessary to diagnose these tumors.

**Correct Answer:** C. Metanephrines

✓ Correct Answer: D. Vanillylmandelic acid VMA