Crystalluria: A neglected aspect of urinary sediment analysis

Crystalluria is a frequent finding in the routine examination of urine sediments. In most instances the precipitation of crystals of calcium oxalate, uric acid, triple phosphate, calcium phosphate and amorphous phosphates or urates is caused by transient supersaturation of the urine, ingestion of foods, or by changes of urine temperature and/or pH which occur upon standing after micturition. In a minority of cases, however, crystalluria is associated with pathological conditions such as urolithiasis, acute uric acid nephropathy, ethylene glycol poisoning, hypereosinophilic syndrome. In addition, crystalluria can be due to drugs such as sulphadiazine, acyclovir, triamterene, piridoxylate, primidone, which under the influence of various factors can crystallize within the tubular lumina and cause renal damage. In all these instances the study of crystalluria is diagnostically useful and is also important to follow the course of the disease. However, a proper methodological approach is necessary. This includes the handling of freshly voided urine, the knowledge of the urinary pH, and the use of a contrast phase microscope equipped with polarizing filters.