There is no specific gallstone blood test, other than white cell count which can indicate infection anywhere, not just the gallbladder, plus a lot of other tests, none of which give an accurate diagnosis of gallstones. An ultrasound is a useful tool that does - in 90% of cases - detect stones. So an ultrasound is a good idea. If she has swelling in that area, i.e. in the upper right hand quadrant, below the ribs then she probably does have stones. If she can feel the gallbladder it must be a little swollen caused by a stone caught in the neck. If she has no pain she is lucky, but this could change at anytime. Your mom is fortunate to live in Spain where olive oil and lemons are plentiful, always look at the bright side of life.