Factors associated with absent microhematuria in symptomatic urinary stone patients

Introduction: The aim of this study was to identify factors associated with absent hematuria in patients with symptomatic urinary stones. Methods: This retrospective study analyzed the clinical and imaging findings of emergency department patients who underwent computed tomography (CT) for suspected ureteral colic over the past 2 years. All patients also underwent a microscopic urinalysis, and the presence of 4 or more red blood cells/high-power field was defined as microhematuria. Results: A total of 798 patients were included in this study. Of these patients, 750 (94.0%) presented with hematuria, while 48 (6.0%) urine samples did not have evidence of hematuria. The group with an absence of hematuria was more likely to have a lower stone location (located in an area from the distal ureter to the bladder) and perinephric stranding on CT than the hematuria group (75.0% vs. 54.3%, p = 0.005; 47.9% vs. 30.5%, p = 0.012, respectively). The degree of hematuria at each stone location was significantly different (p = 0.001). In multivariate analysis, perinephric stranding (odds ratios (OR) 1.87 [95% confidence interval (CI) 1.01–3.46], p = 0.047), a lower stone location (OR 2.72 [95% CI 1.37–5.36], p = 0.004), and elevated serum blood urea nitrogen (BUN) levels (OR 1.06 [95% CI 1.01–1.12], p = 0.026) were associated with absent hematuria. Conclusions: In this large cohort of patients with renal colic, 6% had no microhematuria. Although some CT findings and elevated BUN were independently associated with hematuria absence, there was no difference in the demographics, time of presentation and degree and location of pain between the groups.