Funcion Hepatica

Approach to the patient with abnormal liver function tests
INTRODUCTION — This topic review will provide an overview on the evaluation of patients with abnormal liver biochemical tests. Detailed discussions on the individual tests and patterns of abnormalities are presented separately. (Search on "Liver function tests" in the main search menu or search on the individual disease). The AmericanGastroenterological Association (AGA) guideline for the evaluation of liver chemistry tests [1], as well as other AGA guidelines, can be accessed through the AGA web site at http://www.gastro.org/practice/medical-position-statements.

DEFINITIONS — Although the term "liver function tests" (LFTs) is commonly used, it is imprecise since many of the tests reflecting the health of the liver are notdirect measures of its function. Furthermore, the commonly used liver function tests may be abnormal even in patients with a healthy liver.

The most common laboratory measures classified as LFTs include the enzyme tests (principally the serum aminotransferases, alkaline phosphatase, and gamma glutamyl transpeptidase), tests of synthetic function (principally the serum albumin concentration andprothrombin time), and the serum bilirubin, which measures the liver's ability to detoxify metabolites and transport organic anions into bile.

The term "liver function tests" will be used to denote these tests throughout this discussion unless particular tests are specified. There are two aminotransferases: alanine aminotransferase (ALT, formerly called SGPT), and aspartate aminotransferase (AST,formerly called SGOT).

EPIDEMIOLOGY — Abnormal LFTs are frequently detected in asymptomatic patients since many screening test panels now routinely include them [2]. A population-based survey in the United States conducted between 1999 and 2002 estimated that an abnormal ALT was present in 8.9 percent of respondents (representing a significant increase compared with results of a similar survey from adecade earlier) [3]. This may be related to the increase in obesity that has also occurred during this same time period. The serum ALT correlates with body mass index (BMI) and waist circumference, and the BMI of Americans has increased significantly [4-6].

Studies evaluating the clinical significance of these abnormalities have produced variable findings, although most have demonstrated thatserious underlying liver disease is uncommon. The differences among individual studies reflect variation in the prevalence of liver disease in the populations that have been studied and the degree to which an underlying cause of the abnormalities was sought. Advances in the noninvasive tests to identify the cause of liver disease have permitted a greater understanding of the spectrum of liver diseaseencountered in various patient populations.

The following examples illustrate some of the findings:

Abnormal serum aminotransferase levels (ALT >2.25 SD above normal; >55 IU/L) were detected in 99 of 19,877 (0.5 percent) Air Force recruits beginning basic training [7]. Of these, a cause was found in only 12 (including chronic hepatitis B and C, autoimmune hepatitis, and cholelithiasis). Nospecific diagnosis was established in the remaining 87 patients.The diagnoses observed in two studies that included a total of 249 blood donors with abnormal serum ALT values included [8,9]: alcoholic liver disease (11 to 48 percent); fatty liver (22 to 56 percent); hepatitis C (17 to 20 percent); miscellaneous causes (4 to 8 percent); and no specific diagnosis (2 to 9 percent).Another studyfocused on 81 of 1124 patients who were referred for abnormal serum aminotransferase levels in whom a diagnosis could not be inferred noninvasively [10]. A liver biopsy revealed steatosis or steatohepatitis in the majority of patients (84 percent); six patients had fibrosis or cirrhosis, and eight had normal histologic findings.A fourth study included 354 patients who underwent a liver biopsy to...