The role of serum and urinary markers in predicting obstructing ureteral stones and reducing unjustified non-contrast computerized tomographic scans in emergency departments.

Introduction: The reported yield of non-contrast computed tomography (NCCT) in assessing flank pain and obstructive urolithiasis (OU) in emergency departments (EDs) is only ~ 50%. We investigated the potential capability of serum and urinary markers to predict OU and improve the yield of NCCT in EDs.

Methods: All consecutive ED patients with acute flank pain suggestive of OU and assessed by NCCT between December 2019 and February 2020 were enrolled. Serum white blood cells (WBC), C-reactive protein (CRP) and creatinine (Cr) levels, and urine dipstick results were analyzed for association with OU, and unjustified NCCT scan rates were calculated.

Results: NCCTs diagnosed OU in 108 of the 200 study patients (54%). The median WBC, CRP, and Cr values were 9,100/µL, 4.3 mg/L, and 1 mg/dL, respectively. Using ROC curves, WBC = 10,000/µL and Cr = 0.95 mg/dl were the most accurate thresholds to predict OU. Only WBC ≥ 10,000/µL (OR = 3.7, 95% CI 1.6-8.3, p = 0.002) and Cr ≥ 0.95 mg/dl (OR = 5, 95% CI 2.3-11, p < 0.001) were associated with OU. Positive predictive value and specificity for detecting OU among patients with combined WBC ≥ 10,000 and Cr ≥ 0.95 were 83% and 89%, respectively. Patients negative to the serum markers criteria underwent significantly more unjustified NCCTs (p = 0.03). The negative predictive value of the serum criteria for justified NCCT scanning was 81%.

Conclusions: WBC and Cr may be valuable serum markers in predicting OU among patients presenting to EDs with acute flank pain. They may potentially reduce the number of unjustified NCCT scans in the ED setting.