Increased 5 Hydroxy-Indole-acetic acid in urine is seen in:

Carcinoid tumors are neuroendocrine tumors of Argentaffin cells that secrete serotonin. 5 Hydroxy-Indole-acetic acid(5-HIAA) is a metabolites of Tryptophan/Serotonin that is clasically elevated in typical carcinoid tumors. Urinary excretion of HIAA is diagnostic test for identification of Carcinoid tumors. Carcinoid Tumors: Carcinoid tumors are neuroendocrine tumors of Argentaffin cells that secrete excess serotonin. Ordinarily only 1% of total tryptophan is conveed to serotonin but in carcinoid tumors 50-60% of available tryptophan is conveed to serotonin. The diagnosis of carcinoid syndrome relies on measurement of urinary or plasma serotonin or its metabolites in the urine. Serotonin is typically degraded to 5-HIAA (Hydroxy-indole acetic acid) in presence of monoamine oxidase(MAO) and is excreted in urine. In carcinoid syndrome large amounts of 5-HIAA is formed and is excreted in urine Carcinoid Syndromes may fuher be divided into Typical Carcinoid Syndromes and atypical carcinoid syndromes depending on the metabolites raise in urine and blood. Typical carcinoid syndrome: Elevated levels of Plasma serotonin Elevated levels of urinary (5HIAA) Atypical Carcinoid Syndrome: Plasma serotonin levels are normal Plasma and urinary levels of 5HTP are increased (Urinary 5HIAA may be normal or midly elevated) Ref: Harper