Does kidney stone size correlate with degree of hydronephrosis on focused emergency department ultrasonography?

Abstract

Study objectives: Emergency physicians may make clinical decisions according to kidney stone size. There have been many published studies reporting increased medical complications relating to kidney stone size. However, there is scant literature describing the relationship of kidney stone size with degree of hydronephrosis on focused emergency department (ED) ultrasonography. We hypothesize that kidney stone size does not correlate with degree of hydronephrosis detected by focused ED ultrasonography. Methods: We performed a retrospective pilot study reviewing the medical records of all patients who underwent focused ED renal ultrasonography by emergency medicine residents and attending physicians evaluating for hydronephrosis. Patients who underwent focused ED renal ultrasonography and were diagnosed with nephrolithiasis by noncontrast computed tomography (CT) of the abdomen and pelvis were included in the study group. Emergency ultrasonographers were blinded to CT results. Data were collected on a standard collection tool during an 8-month period from July 1, 2003, to April 1, 2004. Data included kidney stone size on CT, degree of hydronephrosis on CT as interpreted by an attending radiologist, and degree of hydronephrosis as interpreted by the emergency physician performing focused renal ED ultrasonography. Preliminary data were analyzed using analysis of variance statistics. Results: Forty-four patients underwent focused renal ED ultrasonography and were diagnosed with kidney stones on noncontrast CT. Using the emergency sonographer's interpretation of degree of hydronephrosis, 6 patients had no hydronephrosis (mean stone size 4 mm, 95% confidence interval [CI] 1.90 to 6.10 mm), 32 patients had mild hydronephrosis (mean stone size 3.875 mm, 95% CI 3.10 to 4.65 mm), 4 patients had moderate hydronephrosis (mean stone size 4 mm, 95% CI 1.03 to 9.03 mm), and 1 patient had severe hydronephrosis (stone size 4 mm). Although not statistically significant, there is an overall trend toward no correlation between kidney stone size and degree of hydronephrosis. Assuming CT to be the criterion standard, the sensitivity and specificity for focused ED renal ultrasonography were 90% and 97%, respectively (positive likelihood ratio 30, negative likelihood ratio 0.10). Conclusion: In this retrospective pilot study, we found no correlation between kidney stone size and degree of hydronephrosis. Although very sensitive and specific in detecting hydronephrosis, findings of hydronephrosis on focused ED renal ultrasonography may not correlate with the size of kidney stone.