Serum liver chemistry tests, commonly called liver tests, or (mistakenly) liver function tests, are ordered for many reasons. Most laboratories offer these tests as a bundle, and this usually includes:
Bilirubin (breakdown product of the RBC after conjugation in the liver and secretion in biliary system excretion)
Alanine aminotransferase (ALT)
Alkaline phosphatase (ALP)
The following tests may also be included in this bundle:
Aspartate aminotransferase (AST)
Gamma-glutamyl transpeptidase (gamma-GT)
Lactate dehydrogenase (LDH).
Individual tests in these panels are not specific for liver disease. Therefore, pattern recognition is critical. Isolated elevation of liver tests is a less common occurrence in liver diseases, and a non-hepatic source should also be considered in such instances. Assessment of patients with abnormal liver tests should be guided by history, risk for liver disease, duration and severity of clinical findings, presence of comorbidities, and the nature of the liver test abnormality noted.
Traditionally, liver tests abnormalities have been grouped under the following patterns:
Hepatocellular (predominantly ALT and AST elevations)
Cholestatic (predominantly ALP elevation) 
Bilirubin may be elevated in any category of liver disease, and this does not aid in the classification.  Isolated gamma-GT elevations are so common and so often unhelpful that many institutions have chosen to delete this test from their liver test panel.  When other liver tests are abnormal, categorisation according to the pattern found is clinically valuable in the process of finding the possible aetiology of the liver disease. However, liver tests can be abnormally elevated in 1% to 4% of the asymptomatic population, and further investigations reveal that 6% of these patients have no obvious cause for liver disease (liver histology may be normal).   In addition, people with liver disease may have normal tests (16% of patients with hepatitis C and 13% of patients with varying histological damage due to non-alcoholic fatty liver diseases have persistently normal tests).  Liver tests may also be normal in people with hepatitis B who are in the immune-tolerant phase and in the inactive HBsAg carrier state. 
Functional assessment of the liver (evaluating protein synthesis, metabolism, bile production, storage, and detoxification) can be determined by: 
Conventional liver tests such as albumin and INR; these tests reflect the liver function
Scoring systems such as Model for End-Stage Liver Disease (MELD) and Child-Turcotte-Pugh (CTP) score, based on laboratory test results and clinical features.
More definitive assessment can be obtained by quantitative assays. However, these are relatively difficult to perform and are not easily available. Techniques include: 
Non-isotope methodologies such as caffeine clearance, albumin synthesis, and antipyrine clearance
Isotope methodologies such as hepatocyte mass scintigraphy (99mTc-GSA) and aminopyrine breath test (13C or 14C-methyl).
Oxford University Hospitals NHS Foundation Trust
JFLC declares that he has no competing interests.
Dr Jeremy Cobbold would like to gratefully acknowledge Dr William D. Carey and Dr Achuthan Sourianarayanane, the previous contributors to this monograph. WDC is an author of a number of references cited in this monograph. AS declares that he has no competing interests.
Assistant Professor of Medicine
Yale Viral Hepatitis Program
Section of Digestive Diseases
Yale School of Medicine
JKL declares that he has no competing interests.
Senior Lecturer in Hepatology & Honorary Consultant Physician
Liver Research Group
Institute of Biomedical Research
The Medical School
University of Birmingham
PN declares that he has no competing interests.
Associate Professor of Medicine
Division of Digestive and Liver Diseases
University of Texas Southwestern Medical Center
MM is an author of a reference cited in this monograph.
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