One of the primary diagnostic methods indicating the condition of the liver are blood liver tests, commonly referred to as a "liver panel". It consists of tests of specific enzymes related to the functioning of the organ and bilirubin (the main pigment of bile). Liver tests can detect chronic diseases of this organ (e.g. inflammation caused by the B or C virus, steatosis caused by alcohol abuse, or drug-induced injury).
What are AST and ALT?
The two main liver enzymes are:2
- alanine aminotransferase (ALAT, ALT),
- aspartate aminotransferase (AspAT, AST).
Both play an important role in the body as they participate in protein transformation processes. Liver function tests include an assessment of activity of these enzymes, which are found in hepatocytes, i.e. liver cells. In the case of even a mild injury to the liver, regardless of its cause, these enzymes are released into the bloodstream. The greater liver injury, the higher their level in the tested blood.2
What can elevated or decreased levels of AST and ALT mean?
The elevated level of transaminases (AspAT and AlAT) indicates an injury to liver cells.1
When should liver function tests be performed?
The performance of liver function tests should be considered especially when certain medicines are taken or when jaundice, ascites or other symptoms that suggest a chronic liver disease are present:1,5
Pain in the right subcostal region
Upper abdominal discomfort, sensation of pressure, fullness, distension,
Chronic fatigue, feeling of lack of energy, exhaustion,
Sleep disturbances – drowsiness, difficulties falling asleep.
- GGT (gamma-glutamyl transpeptidase): an enzyme associated with cell membranes, occurs mainly in the liver, kidney, pancreas,2
- LDH (lactate dehydrogenase): an enzyme that occurs in all cells of the body. As a result of cell death or increased permeability of cell membranes (caused, for example, by ischaemia or toxins) LDH is released into the bloodstream,2
- Bilirubin: a yellow pigment created by the breakdown of red blood cells. It gives to the bile its characteristic colour. Indirect (unconjugated) bilirubin is formed as a result of breakdown of haemoglobin in red blood cells. The liver transforms this bilirubin into direct (conjugated) bilirubin than can be subsequently released into the bowels through the gallbladder for elimination. This is why the level of total bilirubin may indicate both destruction of red blood cells as well as normal functioning of the liver, gallbladder and bile ducts.1,4
- AST: <40 IU/l,
- ALT: <40 IU/l,
- GGT: <35 IU/l for women and <40 IU/l for men,
- LDH: <480 IU/l in adults,
Other enzymes that are assayed in liver function tests are:
total 5.1-20.5 µmol/l (0.3-1.2 mg/dl)
conjugated 1.7-6.8 µmol/l (0.1-0.4 mg/dl)
unconjugated 3.4-13.7 µmol/l (0.2-0.8 mg/dl).
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Szajewska H et al. Badania diagnostyczne. Wątroba. Interna Szczeklika: Podręcznik chorób wewnętrznych. Medycyna Praktyczna. Kraków 2012: 832–836.
Milkiewicz P. Interpretacja badań laboratoryjnych w chorobach wątroby. Wielka Interna. Gastroenterology, part I, ed. A. Dąbrowski. Medical tribune Poland. Warsaw 2010: 467–471.
Unconjugated Bilirubin - Glossary | Laboratory, radiology, sleep and genetic | Biron, https://www.biron.com/en/glossary/unconjugated-bilirubin/
Essentiale in the treatment of NAFLD, REPORT FROM THE QUANTITATIVE STUDY WITH PHYSICIANS FOR SANOFI, THE MODULE BASED ON PATIENTS’ MEDICAL RECORDS, April 2020. Data on file.