Can Urine Dipstick be Used as a Surrogate for Serum Creatinine in Emergency Department Patients Who Undergo Contrast Studies?

Contrast-induced nephropathy (CIN) is a complication associated with contrasted computed tomography (CT). Elevated creatinine (Cr) is often used to screen for CIN. This study evaluates dipstick urinalysis (Udip) detection of Cr > 1.5 mg/dL. If sufficiently sensitive, Udip results could then be incorporated into future rapid screening protocols for patients undergoing contrast studies. This retrospective record review evaluated all Emergency Department patients over 2 years with documented Udip and serum creatinine results. Patient demographics and pertinent past medical history were also collected. Data were collected on 2421 patient visits, with 241 having Cr > 1.5 mg/dL (9.9%). There were 923 patient visits with a negative Udip (38.1%). Sensitivity and negative predictive value for abnormal Udip in detecting elevated creatinine were 85.5% and 96.2% (p < 0.01), respectively. Thirty-five patient visits (among 26 patients) had negative urine dip and Cr > 1.5 mg/dL, but each reported at least one of the following at triage: prior renal disease, hypertension, diabetes, congestive heart failure, or age > 60 years. Udip is a sensitive screening test, but alone is not accurate enough to predict patients at potential risk for CIN (Cr > 1.5 mg/dL). However, combining Udip results with risk factor screening may allow a rapid method for predicting which patients may safely undergo contrast CT scanning in the ED, but this needs prospective evaluation.