<prompt> A patient with progressive jaundice with clay coloured stool and dark urine. The following investigations can be used, EXCEPT:Oral cholecystographyPTCERCPUSG  <response>: Oral cholecystography is of no value in patients with intestinal malabsorption, vomiting, obstructive jaundice, and hepatic failure. Biliary obstruction causes progressive dilatation of the intrahepatic bile ducts as intrabiliary pressures rise. Hepatic bile flow is suppressed, and reabsorption and regurgitation of conjugated bilirubin into the bloodstream lead to jaundice accompanied by dark urine bilirubinuria and light-colored acholic stools. PTC, ERCP and USG can be used for the evaluation in this patient. Ref: Longo D.L., Fauci A.S., Kasper D.L., Hauser S.L., Jameson J.L., Loscalzo J. 2012. Chapter 311. Diseases of the Gallbladder and Bile Ducts. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo Eds, Harrisons Principles of Internal Medicine, 18e. 