In line with its mission, the Editorial Board of MedTvoiLokony makes every effort to provide reliable medical content supported by the latest scientific knowledge. The additional flag “Checked Content” indicates that the article has been reviewed by or written directly by a physician. This two-step verification: a medical journalist and a doctor allows us to provide the highest quality content in line with current medical knowledge.
Our commitment in this area has been appreciated, among others, by by the Association of Journalists for Health, which awarded the Editorial Board of MedTvoiLokony with the honorary title of the Great Educator.
The liver can be compared to an extensive enterprise whose functions include the production, processing and storage of goods. In order for such an enterprise to be profitable, its activities should be subject to constant, complex control. In the case of the liver, this control is easier – both the correctness of the processes carried out by it and the potential threats to its good condition can be monitored by analyzing our blood.
Laboratory tests of the liver
Laboratory tests of the liver belong to the so-called the basic panel of tests (useful during a health check-up), and are especially recommended for people who have had contact with factors that may damage this organ – take drugs for a long time, abuse alcohol, are suspected of being infected with hepatitis viruses or have symptoms such as, among others. in jaundice, itchy skin or ascites and swelling.
Bilirubin
As mentioned above, jaundice is a symptom of various medical conditions and not a disease in itself. Many of its forms are associated with impaired liver function. A healthy liver is involved in “neutralizing” bilirubin – a toxic product of hemoglobin breakdown from aging red blood cells. Changes take place in the liver that enable its formation and secretion the so-called bound bilirubin (conjugated, direct) to bile, and with it to the gastrointestinal tract and its final excretion in faeces or urine. If an obstruction occurs at any of these stages – the liver is unable to effectively produce or excrete bilirubin in the bile, e.g. due to obstruction of the bile ducts from the liver, bilirubin appears in the blood causing jaundice. The determination of the total amount of bilirubin in the patient’s blood, as well as its fraction – free bilirubin (not yet transformed in the liver) and combined bilirubin – allows to identify the causes of jaundice, and thus facilitates the diagnosis of the underlying disease.
Bile acids
The production of bile, in addition to removing bilirubin, enables the absorption of fats and vitamins soluble in them (A, D, E, K) from the intestine. This is due to the so-called bile acids (BA). Diseases in the liver tissue or disturbances in the flow of bile into the small intestine (cholestasis) increase the level of BA in the blood. In the case of intrahepatic cholestasis in pregnancy, an increase in serum bile acid levels may be the first and only laboratory abnormality.
Liver enzymes
The processes of production and transformation of compounds such as proteins, sugars and fats in the liver are carried out by enzymes. In states of liver damage, they are secreted from its cells into the blood, where their increased activity is observed. The enzymes most often determined in the diagnosis of liver diseases are aminotransferases – alanine (ALT) and aspartate (AST). A significant increase in the activity of ALT is characteristic of inflammatory liver damage (viral infections, alcohol or some drugs), while the predominant increase in the activity of AST is observed in the course of toxic damage, such as in the case of toadstool poisoning. For diagnostic purposes, simultaneous determination of the activity of both transaminases is recommended, as their relationship is important for differentiating the causes of liver damage.
The next liver enzymes whose serum activity increases in the course of diseases of this organ are alkaline phosphatase (ALP) and gamma-glutamylo transferase (GGTP). They are very often used, especially in the diagnosis of biliary diseases. Normal GGTP activity in the blood excludes these diseases, and its increase may also be caused by excessive alcohol consumption or the use of drugs such as barbiturates, phenytoin or estrogens.
Less characteristic of liver disease is a moderate increase in lactate dehydrogenase (LDH). This enzyme is present in all cells in the body, including red blood cells. Increased breakdown of the latter (haemolytic anemia) causes an increase in the release of both this enzyme and hemoglobin, which leads to the accumulation of bilirubin (so-called prehepatic jaundice).
If liver damage is suspected, cholinesterase (ChE) activity should also be measured. This enzyme is produced in the liver and released into the blood from it – hence its reduced activity in the serum indicates a deterioration of the functions of the organ in question, e.g. as a result of poisoning with pesticides.
Coagulation disorders
Liver disease may also manifest itself as a reduced production of proteins by this organ. This fact can be detected directly (e.g. a reduced concentration of liver synthesized albumin in the blood) or indirectly. The latter case concerns the production of fibrinogen and protein coagulation factors (the so-called factors II, VII, IX, X), whose insufficient production causes an extension of the coagulation time in the extrinsic pathway – the so-called prothrombin time (PT) and an increase in INR.
Ammonia
Another important function of the liver is to detoxify the body. This organ filters the blood from poisons from the external environment (e.g. drugs) and from harmful products of metabolism of compounds in our body. For example, disturbances in the neutralizing function of the liver can lead to an increase in blood levels of ammonia, which in turn can result in neuropsychiatric disturbances.
If not a biopsy, then …
Chronic liver diseases lead to damage to the structure of this organ – fibrosis and steatosis. The degree of these changes can be assessed by biopsy, which is, however, a procedure with a risk of complications and limited interpretation. An alternative to this test is a simple determination of the biochemical parameters of the patient’s blood, combined with their analysis using a computer algorithm. Depending on the scope of the disorder assessment, we can perform FibroTest or Fibromax.
The above-mentioned biochemical tests of the liver indicate a malfunction of the organ, but do not provide information about the primary cause of the disease. This knowledge can be obtained using more specialized laboratory tests. They will be discussed in the next episode of this article.