[Analytical methods of calculi and urinary crystals]

Numerous methods can be used for the analysis of urinary stones, but few of them provide information on the structure, chemical composition and crystal phases of these stones. In a good urinary stone analysis the stone is first examined through a binocular magnifying glass, for instance, to detect its structural features including umbilication. Randall's plaque, bracketing faces and individualized or non-individualized nucleus. Morphological typing is important as it points to one pathology or another irrespective of composition. Composition must be determined quantitatively, with differentiation of crystal phases, and this requires global physical methods such as X-ray microdiffractiometry or infrared spectrophotometry. Urinary crystals can be identified by polarized light microscopy supplemented, if necessary, by infrared microscopy when the crystals are few and of unusual morphology. Studying crystalluria is a simple and efficient means of following up lithiasic patients, provided their urine is collected and stored under adequate conditions. In interpreting the results various criteria, and particularly the nature, abundance, size, facies, aggregation and frequency of crystals, must be taken into account.