Crystalluria: a neglected aspect of urinary sediment analysis

Crystalluria is a frequent finding in the routine examinationof urine sediments. In most instances the precipitation of crystalsof calcium oxalate, uric acid, triple phosphate, calcium phosphateand amorphous phosphates or urates is caused by transient supersaturationof the urine, ingestion of foods, or by changes of urine temperatureand/or pH which occur upon standing after micturition. In aminority of cases, however, crystalluria is associated withpathological conditions such as urolithiasis, acute uric acidnephropathy, ethylene glycol poisoning, hypereosinophilic syndrome.In addition, crystalluria can be due to drugs such as sulphadiazine,acyclovir, triamterene, piridoxylate, primidone, which underthe influence of various factors can crystallize within thetubular lumina and cause renal damage. In all these instancesthe study of crystalluria is diagnostically useful and is alsoimportant to follow the course of the disease. However, a propermethodological approach is necessary. This includes the handlingof freshly voided urine, the knowledge of the urinary pH, andthe use of a contrast phase microscope equipped with polarizingfilters.