Can i still have kidney stones even if they don't show up on a ct scan?

Yes, but: Kidney stones that do not contain calcium may not show up very well on a ct. However, these would need to be very small, so whether they are clinically signifcant is questionable. If the ct says no stone, the chances are good that either there is no stone, or it is too small to be worrisome.

Small ones: Smaller than may be 5mm.

? contrast: Small stones can be missed. But if the ct was not a stone-protocol (i.e. Done with contrast) then stones may be missed.

Only tiny ones: Stones 3mm or greater should be visible on ct unless the "slices" are widely spaced.

Possible, not likely: Most kidney stones contain calcium and show up very clearly on ct scan. Some, however, are made up of uric acid and don't show up directly. If they are blocking fluid from moving through the ureter, the ureter above the blockage will be stretched out or dilated, and this is easy to see on ct. So even though some stones don't show up, ones large enough to block the ureter can be detected.