The first test should be gallbladder ultrasound. This frequently diagnostic. If the patient has gallstones and the US isn't definitive regarding acute cholecystitis, a NM HIDA scan is usually confirmatory. In a patient without gallstones who has diabetes, the HIDA scan is useful for detecting acalculous cholecystitis, which can produce a false negative US examination. If the patient has no cholelithiasis or other RUQ (or right kidney) abnormality defined by US, the next examination is an UGI to evaluate the stomach and duodenum. If these two exams are unrevealing an abdominal CT (to specifically evaluate the pancreas) or a gallbladder ejection fraction NM exam (to evaluate biliary function) should be considered. Please note that if the patient has symptoms of pancreatitis CT is preferred instead of US.