I don't practice: I'm a doctor, but not the kind that helps people (according to my mother in law ). I work at Washington University School of Medicine. I'm a chemical engineer working in the biomed field, so I've always had a casual interest in endocrinology, where the systems of the body behave like industrial chemical processes. I sat in on lectures when my wife was having issues with her gall bladder. These reinforced what I was told by MDs in Indiana and at other hospitals in St. Louis: my wife's surgeon, who has performed over 1800 such surgeries in the last 20 years, walked us through this. I called my father (also an MD who wrote a thesis on the chemistry of gall stone formation while at Pitt) who concurred with the course of treatment. The HIDA scan is a method to test gall bladder function. It's not working if it can't expel anything - how is it going to dose your system with bile? Maybe I am completely off base, but it seems unlikely based on the number of surgeons and physicians who gave me the exact same opinion on the same course of treatment.
I was quoting directly for standard practice guidelines. I repeat, HIDA is not required for evaluation of common gallstones/gallbladder disease.
Many people have gallstones, most of these folks are not symptomatic. People that do become symptomatic usually have stones too large to fit through the cystic duct, which causes the gallbladder to contract against a closed opening. This leads to postprandial pain that people experience, which is known as biliary colic.
Do some people have actual intrinsic malfunction of the gallbladder? Sure. But that's not why most people have gallstone and is not why most people have biliary colic. For the most part HIDA scans are used to detect obstruction by detect lack of uptake of tec99 into the gallbladder (suggesting obstruction at the opening).
I'm not making this up. I just confirmed all this information from primary literature, published guidelines from various surgical societies and from synthesized practice guidelines online.