Crystaluria - small crystals in urine

A 63 year old male patient (personal friend) is passing small sand size crystals in urine intermittently, with no other symptoms of stones such as pain, hematuria, etc. No other symptoms of urinary tract dysfunction or gout are reported currently or in past. Chemical analysis of urine sample reveals calcium oxalate and uric acid crystals. The doctor reports there is no evidence of UTI and to have not previously seen this particular presentation and does not know what it means. The doctor agrees to report back after a review of literature and other investigation. Meanwhile, the patient is left with no information on how to manage this problem other than to keep drinking lots of liquids. I have recommended to the patient to seek an expert opinion from a urologist rather than wait for the primary care doctor to make some kind of helpful evaluation. Incidentally, the patient has experienced several other seemingly unrelated medical problems over the past year to 18 months, which are not given here, but may be if this seems important to anyone. I am trying to be a helpful friend since self directed research has led to extreem anxiety in patient. Thanks for any discussion that may help interpret these findings or to help in understanding what the patient may do about it.