<prompt> Answer this question truthfullyWhat are some additional diagnostic tests for cholangitis?  <response>: <reason> Endoscopic retrograde cholangiopancreatography ERCP is considered a gold standard test for diagnosing biliary obstruction. Magnetic resonance cholangiopancreatography MRCP and percutaneous transhepatic cholangiography PTCA are the most sensitive techniques to correctly determine the underlying cause and level of biliary obstruction in patients with acute cholangitis when ERCP fails. 