Did you mean a 0.5 mm stone rather than a 0.5 cm stone? 0.5 mm will probably pass on its own with some discomfort (that's about as big as the thickness of your fingernail). A 0.5 cm (5 mm) stone, however, is fairly large (bigger than a BB). I have passed stones of that size (and some larger), but it definitely isn't fun. I don't want to scare you. A stone of that size isn't likely to physically damage you. It will definitely FEEL like it's doing damage. Sharp pain similar to a SEVERE gas attack that seems to move across the abdomen is my usual symptom. If you have increasing dull pain in the flank (lower back, kidney) area that gets so bad that you can't get comfortable in any position (especially if it keeps you awake), call your doctor right away. This could be a symptom that the stone is blocking the ureter (the tube from your kidney to your bladder). Since your kidney continually produces urine, a blockage causes the kidney to slowly blow up like a balloon. If not treated, this can cause permanent kidney damage.
I have carried stones of that size (and larger) for several months with NO ill effects. My urologist typically isn't concerned until they reach the 7 - 10 mm (1cm) size. Stones that large usually do not pass and must be removed (usually through lithotrypsy). In fact I have a 5X7mm and a 7X10mm stone in my left kidney right now that I am having removed through lithotrypsy next Tuesday.
Hope this info helps you understand what is going on.
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