Clinicians are required to assess abnormal liver chemistries on a daily basis. The most common liver chemistries ordered are serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase and bilirubin. These tests should be termed liver chemistries or liver tests. Hepatocellular injury is defined as disproportionate elevation of AST and ALT levels compared with alkaline phosphatase levels. Cholestatic injury is defined as disproportionate elevation of alkaline phosphatase level as compared with AST and ALT levels. The majority of bilirubin circulates as unconjugated bilirubin and an elevated conjugated bilirubin implies hepatocellular disease or cholestasis. Multiple studies have demonstrated that the presence of an elevated ALT has been associated with increased liver-related mortality. A true healthy normal ALT level ranges from 29 to 33 IU/l for males, 19 to 25 IU/l for females and levels above this should be assessed. The degree of elevation of ALT and or AST in the clinical setting helps guide the evaluation. The evaluation of hepatocellular injury includes testing for viral hepatitis A, B, and C, assessment for nonalcoholic fatty liver disease and alcoholic liver disease, screening for hereditary hemochromatosis, autoimmune hepatitis, Wilson’s disease, and alpha-1 antitrypsin deficiency. In addition, a history of prescribed and over-the-counter medicines should be sought. For the evaluation of an alkaline phosphatase elevation determined to be of hepatic origin, testing for primary biliary cholangitis and primary sclerosing cholangitis should be undertaken. Total bilirubin elevation can occur in either cholestatic or hepatocellular diseases. Elevated total serum bilirubin levels should be fractionated to direct and indirect bilirubin fractions and an elevated serum conjugated bilirubin implies hepatocellular disease or biliary obstruction in most settings. A liver biopsy may be considered when serologic testing and imaging fails to elucidate a diagnosis, to stage a condition, or when multiple diagnoses are possible.

Laboratory liver tests are broadly defined as tests useful in the evaluation and treatment of patients with hepatic dysfunction. The liver carries out metabolism of carbohydrate, protein and fats. Some of the enzymes and the end products of the metabolic pathway which are very sensitive for the abnormality occurred may be considered as biochemical marker of liver dysfunction. Some of the biochemical markers such as serum bilirubin, alanine amino transferase, aspartate amino transferase, ratio of aminotransferases, alkaline phosphatase, gamma glutamyl transferase, 5′ nucleotidase, ceruloplasmin, α-fetoprotein are considered in this article. An isolated or conjugated alteration of biochemical markers of liver damage in patients can challenge the clinicians during the diagnosis of disease related to liver directly or with some other organs. The term “liver chemistry tests” is a frequently used but poorly defined phrase that encompasses the numerous serum chemistries that can be assayed to assess hepatic function and/or injury.

World J Hepatol. 2021 Nov 27; 13(11): 1688–1698.

Liver biochemical tests are some of the most commonly ordered routine tests in the inpatient and outpatient setting, especially with the automatization of testing in this technological era. These tests include aminotransferases, alkaline phosphatase, gamma-glutamyl transferase, bilirubin, albumin, prothrombin time and international normalized ratio (INR). Abnormal liver biochemical tests can be categorized based on the pattern and the magnitude of aminotransferases elevation. Generally, abnormalities in aminotransferases can be classified into a hepatocellular pattern or cholestatic pattern and can be further sub-classified based on the magnitude of aminotransferase elevation to mild [< 5 × upper limit of normal (ULN)], moderate (> 5-< 15 × ULN) and severe (> 15 × ULN). Hepatocellular pattern causes include but are not limited to; non-alcoholic fatty liver disease/non-alcoholic steatohepatitis, alcohol use, chronic viral hepatitis, liver cirrhosis (variable), autoimmune hepatitis, hemochromatosis, Wilson’s disease, alpha-1 antitrypsin deficiency, celiac disease, medication-induced and ischemic hepatitis. Cholestatic pattern causes include but is not limited to; biliary pathology (obstruction, autoimmune), other conditions with hyperbilirubinemia (conjugated and unconjugated). It is crucial to interpret these commonly ordered tests accurately as appropriate further workup, treatment and referral can greatly benefit the patient due to prompt treatment which can improve the natural history of several of the diseases mentioned and possibly reduce the risk of progression to the liver cirrhosis.

The coronavirus pandemic has changed the priorities of the whole medical society. During the clinical course of COVID-19, it has been observed that hepatic injury occurs in a significant proportion of patients, particularly in those with severe or critical illness. In this literature review, we summarize the most recent studies, which covered the pathophysiology of COVID-19 induced liver injury including; hepatic pathological findings, therapy related liver damage, and the effects of the viral infection on pre-existing liver diseasesin context of the most recent recommendations. Conclusions: This review sheds light on the impact of COVID-19 infection on the liver, as well as the prognostic effect of liver laboratory markers on disease outcome. Temporal variations in liver parameters during disease course as well as different patterns of derangement are depicted. More intensive surveillance and individualized therapeutic approaches should be tailored for immunocompromised patients with advanced liver disease, hepatocellular carcinoma, and liver transplant patients. Despite the limited studies on COVID-19 infected patients with preexisting liver disease, this comprehensive overview provides a perspective on the management of liver disease during COVID-19.

Clinical Chemistry December 2000 vol. 46 no. 12 2027-2049

Purpose: To review information on performance characteristics for tests that are commonly used to identify acute and chronic hepatic injury.

Data Sources and Study Selection: A MEDLINE search was performed for key words related to hepatic tests, including quality specifications, aminotransferases, alkaline phosphatase, γ-glutamyltransferase, bilirubin, albumin, ammonia, and viral markers. Abstracts were reviewed, and articles discussing performance of laboratory tests were selected for review. Additional articles were selected from the references.

Guideline Preparation and Review: Drafts of the guidelines were posted on the Internet, presented at the AACC Annual Meeting in 1999, and reviewed by experts. Areas requiring further amplification or literature review were identified for further analysis. Specific recommendations were made based on analysis of published data and evaluated for strength of evidence and clinical impact. The drafts were also reviewed by the Practice Guidelines Committee of the American Association for the Study of Liver Diseases and approved by the committee and the Association’s Council.

Recommendations: Although many specific recommendations are made in the guidelines, some summary recommendations are discussed here. Alanine aminotransferase is the most important test for recognition of acute and chronic hepatic injury. Performance goals should aim for total error of <10% at the upper reference limit to meet clinical needs in monitoring patients with chronic hepatic injury. Laboratories should have age-adjusted reference limits for enzymes in children, and gender-adjusted reference limits for aminotransferases, γ-glutamyltransferase, and total bilirubin in adults. The international normalized ratio should not be the sole method for reporting results of prothrombin time in liver disease; additional research is needed to determine the reporting mechanism that best correlates with functional impairment. Harmonization is needed for alanine aminotransferase activity, and improved standardization for hepatitis C viral RNA measurements.

Zealand Family Physician Journal, 29, 117-120. Volume 34 Number 3, June 2007

This guide (updated from an earlier version published in the NZFP in 20021) is intended to provide easily accessible information on appropriate investigation and likely diagnoses. First view Figure 1, then look at notes as indicated.
• For single enzyme elevations see Note 1. • If multiple enzyme abnormalities refer to Question 1.

Ulster Med J 2012;81(1):30-36

Abstract
Liver enzymes are commonly used in the evaluation of patients with a range of diseases. Classically they are used
to give information on whether a patient’s primary disorder is hepatitic or cholestatic in origin. However, knowledge of enzyme ratios and pattern recognition allow much more information to be derived from these simple tests. This paper offers an insight to generalists on how to extract greater information from these tests in order to improve the investigation and management of liver disease.

[Indian J Pediatr 2007; 74 (7) : 663-671]

ABSTRACT
Liver function tests (LFT) are a helpful screening tool, which are an effective modality to detect hepatic dysfunction. Since the liver performs a variety of functions so no single test is sufficient to provide complete estimate of function of liver. Often clinicians are faced with reports that do not tally with the clinical condition of the patient and they face difficulty in interpreting the LFT. An attempt is being made to study and understand the LFT and simplify their interpretation with algorithms.

Postgrad Med J. 2003 Jun;79(932):307-12

Abstract
Interpretation of abnormalities in liver function tests is a common problem faced by clinicians. This has become more common with the introduction of automated routine laboratory testing. Not all persons with one or more abnormalities in these tests actually have liver disease. The various biochemical tests, their pathophysiology, and an approach to the interpretation of abnormal liver function tests are discussed in this review.

CMAJ • February 1, 2005; 172 (3):367-379

ISOLATED ALTERATIONS OF BIOCHEMICAL MARKERS OF LIVER DAMAGE in a seemingly healthy patient can present a challenge for the clinician. In this review we provide a guide to interpreting alterations to liver enzyme levels. The functional anatomy of the liver and pathophysiology of liver enzyme alteration are briefly reviewed. Using a schematic approach that classifies enzyme alterations as predominantly hepatocellular or predominantly cholestatic, we review abnormal enzymatic activity within the 2 subgroups, the most common causes of enzyme alteration and suggested initial investigations.

Alcohol and Alcoholism 2006 41(3):209-224

“Chronic alcohol consumption is a major cause of liver cirrhosis which, however, develops in only a minority of heavy drinkers. Evidence from twin studies indicates that genetic factors account for at least 50% of individual susceptibility. The contribution of genetic factors to the development of diseases may be investigated either by means of animal experiments, through linkage studies in families of affected patients, or population based case–control studies. With regard to the latter, single nucleotide polymorphisms of genes involved in the degradation of alcohol, antioxidant defense, necroinflammation, and formation and degradation of extracellular matrix are attractive candidates for studying genotype–phenotype associations. However, many associations in early studies were found to be spurious and could not be confirmed in stringently designed investigations. Therefore, future genotype–phenotype studies in alcoholic liver disease should meet certain requirements in order to avoid pure chance observations due to a lack of power, false functional interpretation, and insufficient statistical evaluation.”

Journal of Hepatology 48 (2008) S113–S123

The cross-talk which has taken place in recent years between clinicians and scientists has resulted in a greater understanding of iron metabolism with the discovery of new iron-related genes including the hepcidin gene which plays a critical role in regulating systemic iron homeostasis. Consequently, the distinction between (a) genetic iron-overload disorders including haemochromatosis related to mutations in the HFE, hemojuvelin, transferrin receptor 2 and hepcidin genes and (b) non-haemochromatotic conditions related to mutations in the ferroportin, ceruloplasmin, transferrin and di-metal transporter 1 genes, and (c) acquired iron-overload syndromes has become easier. However, major challenges still remain
which include our understanding of the regulation of hepcidin production, the identification of environmental and genetic modifiers of iron burden and organ damage in iron-overload syndromes, especially HFE haemochromatosis, indications regarding the new oral chelator, deferasirox, and the development of new therapeutic tools interacting with the regulation of iron metabolism.”