Pyuria and Urine Cultures in Patients with Acute Renal Colic

Renal colic caused by stone(s) is common in the emergency department. Often, urinalysis reveals white blood cells, but it is unknown how frequently pyuria is sterile or infectious.

We sought to determine the incidence of pyuria in patients with renal colic and to correlate the incidence with a positive urine culture.

A 1-year retrospective review of adult patients with renal colic presenting to three community emergency departments was performed. Patients without confirmed renal stone(s) or completed urinalysis were excluded. Hematuria is defined as ≥5 red blood cells per high power field (RBC/HPF) and pyuria as >10 white blood cells per high power field (WBC/HPF). A positive urine culture is defined as >100,000 colony forming units per milliliter. Student's t-test, chi square, or Fisher's exact tests were performed as appropriate, with significance set at 0.05.

There were 339 patients who satisfied the inclusion and exclusion criteria, and 14.2% of these patients had associated pyuria. There were 153 (45.1%) urine cultures performed, and 16 (10.5%) were positive. Patients with pyuria were more likely to have a positive urine culture (36.4% vs. 3.3%, respectively; p < 0.001). The percentage of positive urine cultures increased (p < 0.001) with increasing pyuria from 9.1% (10-20 WBC/HPF) to 60.0% (>50 WBC/HPF). Positive cultures also increased (p < 0.001) with increased leukocyte esterase observed on macroscopic samples, from 1.6% (small or less leukocyte esterase) to 77.8% (large-volume leukocyte esterase).

Pyuria was found in 14.2% of patients with renal colic. Patients with pyuria had 36.4% positive cultures compared to 3.3% of patients without pyuria. The degree of pyuria or leukocyte esterase was significantly associated with the risk of a positive culture. Urine cultures are recommended for all patients with renal colic and pyuria.