What is the clinical significance of the urinalysis in patients with renal stones?
Most stone formers have macroscopic or microscopic hematuria and may have some crystalluria. The remainder of the urinalysis is usually normal. Crystals are normally absent in warm and freshly voided urine, and if present suggest a diagnosis. However, most urine specimens cool before examination, and crystals may form in normal urine with time and cooling. Thus, by the time urine is usually examined, the finding of crystalluria may have little clinical significance. An exception is the presence of cystine crystals, which are diagnostic of cystinuria. Persistently acidic urine (pH < 5.5) suggests uric acid or cystine stones. More alkaline urine (pH > 6.5–7.0) suggests calcium phosphate stones. Persistently alkaline urine (pH > 7.0–7.5) suggests the presence of urea-splitting organisms, such as Proteus, Pseudomonas, or Klebsiella species that cause recurrent urinary tract infections and strongly suggests struvite stones. Struvite stones never form unless the urine pH is alkaline.