I have gallbladder sludge but the doctorss aren't sure if stones are there. i had hida, catscan, and cck injections performed but docs are not sure if gallstones are present. why can't they tell?

There is a reason: Sludge is formed in a diseased gall bladder ( do not form in healthy gall bladder ) in time these dust like particles will form as gall stones , also some times cholesterol stones also called strawberry gb( gives severe inflammation ) is interpreted as sludge or as gb polyps , if symptoms are severe enough need cholecystecomy not more tests.

Not sure: "sludge" is a non-specific term. Usually refers to viscous/thick junk , gravity dependent in the gall-bladder. Have you had an ultasound, that would help

Not sure: You have had the full workup except the mrcp. If you are not having symptoms, stop having tests. If after all these tests they still do not definitively see stones then stop. If you are symptomatic you might have some other process going on that mimics gallstones. What symptoms do you have to make them suspect gallstones as the cause.? Are you seeing a liver doctor or general practitioner?

Gallstone types..: There are several types of gallstones including cholesterol stones, pigment stones, and mixed stones. Certain stones show up better on certain types of imaging.

US for some stones: Sometimes gall stones are not calcified and are not opaque on CT scan and not detected.HIDA scan shows function and not anatomy. US study is most accurate in showing gall stones and sludge.