Screening for Renal Insufficiency in ED Patients with Severe Hypertension
Abstract & Commentary
Source: Karras DJ, et al. Urine dipstick as a screening test for serum creatinine elevation in emergency department patients with severe hypertension. Acad Emerg Med 2002; 9:27-34.
As many as 32% of patients seeking care in urban emergency departments (EDs) present with elevated blood pressure (BP) readings, and between 2-5% present with severely elevated BPs. The Sixth Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC-VI), recognized as the national standard for the evaluation and management of hypertension, recommends extensive evaluation looking for end-organ damage among patients with severely elevated BPs. Most emergency medicine texts recommend this same extensive work-up, even in the asymptomatic patient, citing the JNC-VI criteria. As part of this work-up, serum creatinine (Cr) testing and urinalysis are recommended to rule out hypertensive renal dysfunction.
This prospective, observational study sought to evaluate the utility of the urine dipstick test in screening for the presence of acute Cr elevation among ED patients with severely elevated BPs. Adult patients with diastolic BPs of 115 or greater were included, and serum Cr and urine dipstick tests were performed. Exclusion criteria were menstruation, pregnancy, urinary tract infection, trauma, dialysis dependence, or renal insufficiency without a known baseline Cr. The investigators examined the performance of the urine dipstick tests for hematuria and proteinuria in identifying an elevated Cr, defined as Cr greater than 1.2 mg/dL or Cr greater than 25% above baseline.
One hundred forty-three patients met the study criteria, with 24 having elevated Cr. The presence of any degree of either proteinuria or hematuria identified these patients with 100% sensitivity and 30% specificity. When defining an abnormal dipstick test as either hematuria in any amount or 1+ or greater proteinuria, sensitivity remained 100% and specificity rose to 42%.
The authors conclude that the urine dipstick test may be an effective screening tool for identifying Cr elevation among patients with severe hypertension. Using the more restrictive definition of an abnormal dipstick would increase the specificity of the test without sacrificing sensitivity.
Commentary by Jacob W. Ufberg, MD
As the authors point out, this small sample size of 24 elevated Cr values is appropriate for the derivation of a prediction rule. However, a larger validation study is needed before the urine dipstick can be widely used to avoid serum Cr determinations in severely hypertensive ED patients. Perhaps the more important question is whether asymptomatic patients with very elevated BPs need any work-up other than a careful physical examination. The JNC-VI criteria were created with the office practitioner in mind, and do not provide any recommendations for the care of patients in acute care settings such as the ED. However, most emergency medicine texts continue to cite the JNC-VI in their recommendation of extensive ED evaluations for patients with severely elevated BPs.
Little, if any, literature exists examining the utility of these workups in the asymptomatic ED patient, and many emergency physicians do not perform any testing in this population. Hopefully, this study is a small first step toward a set of evidence-based recommendations for the ED setting which may reduce the time and money spent (perhaps needlessly) on the ED patient with asymptomatic severe hypertension.
Dr. Ufberg, Assistant Professor of Emergency Medicine, Department of Emergency Medicine, Temple University School of Medicine, Philadelphia, Pa., is on the Editorial Board of Emergency Medicine Alert.