Duodenal biliary drainage: A procedure used to diagnose gallstones when suspicion is high but other tests are negative. A thin tube is passed through a nostril down the throat, through the esophagus and stomach, into the duodenum. Once the tube is in place, a synthetic hormone related to cholecystokinin is injected IV. It causes the gallbladder to contract and squeeze out bile into the duodenum. The bile then is sucked up through the tube and examined for the presence of cholesterol and pigment particles under a microscope. A modification of duodenal biliary drainage involves collection of bile through an endoscope at the time of EGD (esophagogastroduodenoscopy) or ERCP (endoscopic retrograde cholangio-pancreatography).