Again, acute RUQ pain (especially in an obese woman) should set off the gallstone alarms. Fever and other systemic signs, white count, etc lead you down the acute cholecystitis. Simple pain leads you to symptomatic cholelithiasis. Either way the first step is to get a RUQ sono to see those stones! HIDA is used as an adjunctive study in cases of cholelithiasis to assess for cystic duct obstruction (and thus likely acute cholecystitis) in equivocal cases.

I thought I heard in a Divine podcast that if the labs showed pretty clear gallstone pancreatitis you could just skip the US and go right to ERCP. Guess not.