The AST to ALT Ratio: A Pattern Worth Considering
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COMPLEX CLINICAL ISSUES (SA HARRISON AND NS REAU, SECTION EDITORS)
The AST to ALT Ratio: A Pattern Worth Considering Jeremy P. Domanski & Stephen A. Harrison
Published online: 29 January 2013 # Springer Science+Business Media New York (outside the USA) 2013
Abstract Elevated liver chemistries are common, with multiple proposed evaluation algorithms to investigate an extensive differential diagnosis. One simple and inexpensive set of laboratory parameters which can guide the evaluation of elevated liver chemistries and is often overlooked is the AST to ALT ratio (AAR). Immediately available, this simple ratio can offer important clues to the underlying etiology and may offer prognostic information for patients with chronic liver disease. In this review, we examine the utility of the AAR in evaluating patients with elevated liver chemistries and suggest a differential diagnosis for an AAR of >1. Keywords AAR . Liver enzymes . AST . ALT . Cirrhosis
Introduction Elevated liver chemistries are a common cause of both inpatient and outpatient referrals to gastroenterology and hepatology. The term “liver chemistries” is preferred to the commonly used term, “liver function tests,” as many of the liver chemistries do not reflect actual liver function [1]. Liver chemistries refer to a group of laboratory measures which have the potential to identify liver injury or disease. This typically includes the aminotransferases aspartate aminotransferase (AST) and alanine aminotransferase (ALT), the enzymes alkaline phosphatase (ALP) and γ- glutamyltransferase (GGT), and measures of synthetic function prothrombin time (PT), albumin and bilirubin. Additional liver chemistries may include lactate dehydrogenase (LDH), international normalized ratio (INR), 5’-nucleotidase, and bile acids. Elevated liver chemistries are common and often J. P. Domanski (*) : S. A. Harrison Division of Gastroenterology and Hepatology, Department of Medicine, Brooke Army Medical Center, Fort Sam Houston, San Antonio, TX 78234, USA e-mail: [email protected]
found in the context of screening examinations. Studies of patients in the United States suggest that between 0.5 and 8.9 % of asymptomatic patients have an elevated ALT [2, 3]. The cost of an extensive evaluation may exceed $3000 based on 2001–2002 fees [4]. However, the clinical context and pattern of elevation can often narrow the differential diagnosis significantly and guide the clinician toward a more focused and efficient evaluation. Historically, the approach to elevated liver chemistry has focused on several patterns: hepatocellular vs cholestatic, acute vs chronic, and mild/moderate vs severe elevations. One often-overlooked pattern is the AAR and the goal of this review is to outline the utility of this ratio in evaluating the patient with elevated liver chemistries as well as patient’s with known chronic liver disease. The serum aminotransferases, AST and ALT, are intracellular enzymes which serve as markers of acute hepatocellular injury. AST is found predominately in the mitochond
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