Kidney stones can be diagnosed by various modalities like plain x-ray of the abdomen, ultrasound, intravenous pyelography but the diagnostic test of choice is a CT scan only as it not only tells the exact location of the kidney stone but also the size and whether it’s producing any harmful effects on the kidneys due to the obstruction.
Hence, CT scan should be done in all cases. Another benefit of the CT scan is that if the preliminary diagnosis of kidney stones is wrong, then the CT scan can also pick up any pathology of the neighboring organs like pancreas, appendix, aorta etc.
I sincerely hope that helps. Please do keep me posted. Warm regards.