Bulk OEM Reagents (Reagent 1/ Reagent 2) for automated chemistry analyzers. 5-Hydroxyindoleacetic acid (5-HIAA) is a metabolite of serotonin released by carcinoid tumors. Therapeutic monitoring by determining 5-HIAA concentration in urine is often required. A narrow healthy range necessitates an accurate and reliable means for the measurement of 5-HIAA concentration. A high throughput detection method with high sensitivity and specificity is presented herein. Serotonin Metabolite 5-HIAA Assay provides a convenient and efficient method to measure 5-HIAA concentration in urine.