The 5-HIAA 2nd Day test is advised in suspected carcinoid tumors with excess serotonin production. It is useful in evaluating symptomatic carcinoid syndrome. Additionally, diagnose gastrointestinal tract and bronchial carcinoid tumors. The test is performed by measuring 5-HIAA levels in urine collected over 48 hours. Elevated levels at 48 hours provide better insights about serotonin production and metabolism, aiding in the management of carcinoid tumors.