Is hida scan accurate if you don't have symptoms/pain at the time of test?

Yes. A hida scan is used to evaluate for acute cholecystitis with an overall accuracy of 98% (pain or not)...Although it would be very unusual to have acute cholecystitis without pain. However, it can happen if someone has diabetes, is on steroids or other pain medications.
Not always. Do not necessarily have to have symptoms during test. The gb ejection fraction and clinical symptoms of biliary pain are correlated. Many times nausea or pain do occur following fatty meal or CCK stimulation of gall bladder to contract.
Possibly. Hida scan with Kinevac injection is usually done to see if the pain that you're initially complaining about is due to abnormally painful contraction of the gallbladder referred to as gallbladder dyskinesis. This provacative test is usually done if your ultrasound did not reveal stones in the gallbladder. The hida scan is a functional test to see if your gallbladder is functioning properly.
It can be. See below. Was Kinevac used? Hida scan with Kinevac (generic name sincalide) allows for evaluation of gallbladder emptying. Sometimes hida scan alone appears normal, but gallbladder is not functioning (emptying) well, which can cause pain (possibly spasms). Amount of emptying is called the ejection fraction and normal is generally greater than 50%.