Can bedside ultrasound assist in determining whether serum creatinine is elevated in cases of acute urinary retention?

Background: There are no guidelines to determine which patients with acute urinary retention (AUR) require blood testing (i.e., serum creatinine) to assess for renal failure. Objective: To determine if hydronephrosis on bedside ultrasound correlates with an abnormal serum creatinine (Cr) level in cases of AUR. Methods: This was a prospective, observational study of subjects clinically diagnosed with AUR at two associated urban academic centers from October 2004 through August 2006. Emergency physicians completed a data form and performed a bedside ultrasound to determine the presence or absence of hydronephrosis. The data collected included suspected cause of AUR, amount of urinary output after Foley insertion, and blood test results. Follow-up was obtained by telephone and electronic medical record for 1 month. Standard statistics were employed. Results: Among 96 enrolled subjects with AUR, 43 had a serum Cr level obtained on the initial visit, and 10 (23%; 95% confidence interval [CI] 1136) of these had an elevated Cr (10% [95% CI 416] of the study cohort). The test characteristics of hydronephrosis on bedside ultrasound to detect elevation in Cr were a sensitivity, specificity, positive predictive value, and negative predictive value of 70%, 67%, 39%, and 88%, respectively. Conclusion: In cases of AUR, the prevalence of elevated creatinine is high, and hydronephrosis based on bedside ultrasonography does not correlate with elevation in creatinine.