Which metabolite is often elevated in carcinoid tumors of the intestine?

The metabolite that is frequently elevated in carcinoid tumors of the intestine is 5-Hydroxyindolacetic acid (5-HIAA). Carcinoid tumors are neuroendocrine tumors that often secrete serotonin, a neurotransmitter that can be metabolized into 5-HIAA. This metabolite is then excreted in the urine, and elevated levels are commonly used as a diagnostic marker for carcinoid syndrome.

When these tumors occur, particularly in the gastrointestinal tract, they can lead to an overproduction of serotonin, which consequently raises the levels of 5-HIAA. Measuring urinary 5-HIAA levels is a critical step in the diagnosis of carcinoid tumors, helping clinicians confirm the presence of these tumors and monitor treatment response.

The other metabolites listed are not specifically associated with carcinoid tumors. For instance, 3-Methoxy-4-hydroxyphenylglycol (MHPG) is primarily a metabolite of norepinephrine and its levels are typically used in the assessment of conditions like pheochromocytoma or other adrenergic tumors. Similarly, 3-Methoxydopamine is a metabolite of dopamine and is not specific to carcinoid tumors.