Liver blood tests are routinely used in diagnosis and management of hepatobiliary disease. Abnormal liver blood test results are often the first indicator of hepatobiliary disease and a common indication for abdominal imaging with ultrasound, computed tomography, or magnetic resonance imaging.[1] 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 red blood cells after conjugation in the liver and secretion in biliary system excretion)
- Alanine aminotransferase (ALT)
- Alkaline phosphatase (ALP)
- Serum albumin.
The following tests may also be included in this bundle:
- Aspartate aminotransferase (AST)
- Gamma glutamyl transferase (gamma-GT)
- Lactate dehydrogenase.
Individual tests in these panels are not specific for liver disease. Therefore, pattern recognition is critical. Evaluation 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 symptoms, the nature of the liver test abnormality noted, and relevant scans and biopsies.[2]
Traditionally, liver test abnormalities have been grouped under the following patterns:[3]
- Hepatocellular (predominantly ALT and AST elevations)
- Cholestatic (predominantly ALP elevation)
- Mixed/infiltrative (elevation of both ALT/AST and ALP).
Isolated elevation of liver tests is a less common occurrence in liver diseases, and a nonhepatic source should be considered in such instances. Bilirubin may be elevated in any category of liver disease.[4] 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.[5] When other liver tests are abnormal, categorization according to pattern is helpful to determine the probable etiology.
Clinical correlation is essential when interpreting liver tests. Liver tests are abnormally elevated in 1% to 9% of the asymptomatic population.[6] Further investigations with diagnostic serology and liver biopsy are normal in 6% of these patients.[7] Importantly, people with chronic liver disease or cirrhosis may have normal liver tests.[8] [9]
Liver tests are markers of liver injury, not liver function.[3] Functional assessment of the liver (evaluation of protein synthesis, metabolism, bile production, storage, and detoxification) can be determined by:
- Conventional liver tests such as albumin and international normalized ratio
- Scoring systems such as Model for End-Stage Liver Disease and Child-Turcotte-Pugh score, based on laboratory test results and clinical features.
