[Clinical value of crystalluria study]

Crystalluria is a marker of urine supersaturation present in both normal and pathological conditions. Indeed, nature and characteristics of the spontaneous crystalluria are of clinical interest for detecting and following biological disorders involved in renal diseases. Method. Crystalluria examination should preferably be performed on first morning urine or fresh fasting voiding samples by polarised microscopy in a Malassez cell. Urine samples must be stored at 37 degrees C or at room temperature and examined within two hours following voiding. Results and discussion. Crystalluria should be interpreted according to various criteria: 1) chemical nature of crystals for abnormal crystals such as struvite, ammonium urate, cystine, dihydroxyadenine, xanthine or drugs; 2) crystalline phase of common chemical species as calcium oxalates, calcium phosphates and uric acids; 3) crystal morphology (calcium oxalates); 4) crystal size (calcium oxalates); 5) crystal abundance (calcium oxalates, calcium phosphates, uric acids, cystine); 6) crystal aggregation (calcium oxalates); 7) frequency of crystalluria assessed on serial first morning urine samples, a very useful tool for long-term surveillance of patients. Within calcium oxalate crystalluria, presence of whewellite is a marker of elevated oxalate concentration (urine oxalate > 0.3 mmol/L); a crystal number > 200/mm 3 is highly suggestive of heavy hyperoxaluria of genetic or absorptive origin. Predominant weddellite crystalluria is most often indicative of an excessive urine calcium concentration (> 3.8 mmol/L); a dodecahedric aspect of the crystals is a marker for heavy hypercalciuria (> 6 mmol/L) while an increased crystal size (>or= 35 microm) is indicative of simultaneous hypercalciuria and hyperoxaluria. Calculation of the global crystal volume, especially when applied to calcium oxalates or cystine, is a clinically useful tool for the monitoring of patients suffering from primary hyperoxaluria or cystinuria. Lastly, presence of crystalluria in more than 50% of serial first voided morning urine samples is in our experience the most reliable biological marker for detecting the risk of stone recurrence in lithiasic patients. Conclusion. Crystalluria examination is an essential laboratory test for detecting and following pathological conditions, which may induce renal stone disease or alter kidney function due to urine crystals.