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.