What is the role of urinalysis in the diagnosis of nephrolithiasis?

Updated: Jun 21, 2018
  • Author: Chirag N Dave, MD; Chief Editor: Bradley Fields Schwartz, DO, FACS  more...
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Answer

Microscopic examination of the urine for evidence of hematuria and infection is a critical part of the evaluation of a patient thought to have renal colic. Gross or microscopic hematuria is only present in approximately 85% of patients with urinary calculi. The lack of microscopic hematuria does not eliminate renal colic as a potential diagnosis. In addition to a dipstick evaluation, always perform a microscopic urinalysis in these patients.

One retrospective study found that 67% of patients with ureterolithiasis had more than 5 red blood cells (RBCs) per high-power field (hpf), and 89% of patients had more than 0 RBCs/hpf on urine microscopic examination. [22] In addition, 94.5% have hematuria if screened with microscopy plus urine dipstick testing. [23]

Degree of hematuria is not predictive of stone size or likelihood of passage. No literature exists to support the theory that ureterolithiasis without hematuria is indicative of complete ureteral obstruction.

Attention should also be paid to the presence or absence of leukocytes, crystals, and bacteria and to the urinary pH. In general, if the number of white blood cells (WBCs) in the urine is greater than 10 cells per high-power field or greater than the number of RBCs, suspect a UTI. Pyuria (>5 WBCs/hpf on a centrifuged specimen) in a patient with ureterolithiasis should prompt a careful search for signs of infected hydronephrosis.

Urinary crystals of calcium oxalate, uric acid, or cystine may occasionally be found upon urinalysis. When present, these crystals are very good clues to the underlying type and nature of any obstructing calculus.

Determining urinary pH also helps. A urine pH greater than 7 suggests presence of urea-splitting organisms, such as Proteus, Pseudomonas, or Klebsiella species, and struvite stones. A urine pH less than 5 suggests uric acid stones.


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