Kidney stones, uric acid stones, as well as xanthinuria can all be considered for the crystals in the urine.
Xanthinuria is the urinary excretion of the purine base xanthine. This is normally caused by a hereditary disorder. This can occur in children as young as 10 years in age.
Lab tests include a 24-hr urine test, blood tests looking for kidney dysfunction, as well as more specific tests looking for xanthine and hypoxanthine blood levels. You already have had many imaging tests, which would evaluate for the more serious causes.
Another more specialized test would be an allopurinol challenge test, which can be discussed with your urologist.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
Medical Weblog:
kevinmd_b