5-HIAA, Urine

Laboratory assay overview

A serotonin analysis is most frequently performed for the diagnosis of carcinoid tumors of the enterochromaffin (Kultschitzsky) cells of the small intestine. These tumor cells release large amounts of serotonin, which can produce the clinical syndrome of flushing, diarrhea, and right-sided heart failure. The most frequently used diagnostic test for carcinoid tumors is 5-HIAA, the final metabolite of serotonin. Diagnose carcinoid tumors and syndrome; values >25 mg/24 hours (higher if the patient has malabsorption) are strong evidence for carcinoid.

Laboratory assay overview

This test is intended for the diagnosis and monitoring of inherited disorders affecting multiple metabolic pathways. Organic acidurias are inherited disorders resulting from a deficient enzyme or transport protein. Although most are autosomal recessive disorders, several are X-linked. The more than 60 described organic acidurias affect many metabolic pathways including amino acid metabolism, lipid metabolism, purine and pyrimidine metabolism, the urea cycle, the Krebs cycle and fatty acid oxidation. These disorders are characterized by a wide variety of symptoms such as lethargy, coma, hypotonia, seizures, ataxia, vomiting, failure to thrive, developmental delay, liver disease, neutropenia, thrombocytopenia, osteomalacia and osteoporosis. Severity of presentation is highly variable as is age of onset, and patients may not present with the most characteristic features. Laboratory results commonly indicate metabolic acidosis, increased anion gap, hyperammonemia, hypoglycemia, lactic acidemia, ketosis, or abnormal lipid patterns. Treatment may be based on dietary restrictions and/or supplementation with cofactors (e.g., riboflavin or cobalamin) or conjugating agents (e.g., carnitine or sodium benzoate); however, there is no effective therapy for some of the disorders. Elevation of one or more organic acids is diagnostic for an organic aciduria; however, elevations should be interpreted in context with clinical findings and/or additional test results. See additional information for a table of selected organic acidurias and associated organic acid elevations. Since many organic acidurias are episodic, the diagnostic efficacy is maximized when the patient is expressing symptoms at the time of specimen collection. The test will be capable of diagnosing over 30 inherited metabolic defects, and will also allow physicians to determine dietary compliance or the effectiveness of dietary/cofactor therapy for their patients. It can also be used, alone or in conjunction with other tests, to confirm the findings of a positive expanded newborn screen.