Liver tests: the essence of the method and interpretation of the analysis

2023 Author: Alfred Shackley | [email protected]. Last modified: 2023-05-21 13:14

A biochemical blood test is a comprehensive study with which you can find out about the functional state of many organs. Laboratory tests that characterize the condition of the liver are called liver function tests.

Deciphering this analysis helps to identify organ pathologies by the amount of certain substances that blood contains.

What is a liver function blood test?

Liver tests are a complex of biochemical tests that can be used to determine the level of certain enzymes and substances that blood contains. These indicators make it possible to assess the structural and functional state of the liver. For the procedure, blood is taken from the patient from a vein in the bend of the elbow on an empty stomach.

Liver tests include the following tests:

• ALT (alanine aminotransferase);
• GTT (gamma glutamyl transferase);
• AST (aspartate aminotransferase);
• Bilirubin (indirect, direct and general);
• Alkaline phosphatase;
• Albumen;
• Thymol test;
• Total protein.

Liver tests are prescribed for patients who complain of heaviness in the right side, frequent nausea, vomiting, yellowing of the skin, as well as an unreasonable increase in body temperature.

Specific indications for this biochemical blood test are the following conditions:

• chronic liver disease caused by alcohol abuse;
• diabetes;
• structural changes in the liver, identified by ultrasound;
• an increase in the rate of iron in the blood serum;
• hepatitis of any etiology.

An analysis for liver function tests should be prescribed if the patient is taking medications that negatively affect the health of the liver. Timely detection of deviations in enzyme indices allows you to make adjustments to the treatment.

Blood test for liver function tests: how to prepare for the test?

A biochemical blood test for liver function tests requires special preparation.

To get accurate results for this laboratory test, follow these rules:

• two days before your blood sample is taken, refrain from increased physical exertion;
• stop drinking alcohol;
• refrain from smoking;
• limit the use of junk food;
• eight hours before your blood sample is taken, refuse to take any food;
• Stop taking medications two weeks before doing the biochemical blood test.

To get an accurate result of liver tests, it is necessary to come to the medical laboratory in the morning between seven and eleven o'clock. Before performing the analysis, it is allowed to drink non-carbonated water.

There are factors that can cause errors in the analysis results.

These include:

• non-compliance with the rules of preparation for the procedure;
• overweight;
• taking certain medications;
• excessive compression of the vein with a tourniquet;
• pregnancy;
• vegetarian diet;
• sedentary lifestyle.

If the doctor has doubts about the accuracy of the results, the analysis can be repeated.

Decoding liver tests

The results of a biochemical blood test are compared with the indicators of the norm, which the laboratory specialists indicate without fail. Deciphering the values of liver function tests is performed taking into account the clinical picture of a particular patient and risk factors such as medication and alcohol consumption.

A special table showing the indicators of liver functioning helps the doctor to identify a deviation from the norm. Any abnormal values need to be decoded only taking into account the clinical picture of the disease. The accuracy of the results depends on the specific equipment used in the laboratory.

Deciphering liver tests includes an assessment of such indicators:

• ALT. The norm of this enzyme for women is 10-35 U / liter, and for the stronger sex - 10-50 U / liter. An increase in ALT indicates viral hepatitis, cirrhosis, alcohol poisoning, and the presence of parasites in the liver;
• AST. This enzyme is found in liver, heart and muscle tissues. The AST norm for women is 11-36 U / liter, for men –15-21 U / liter. Deviation from normal values indicates damage to those organs that contain AST. An increase in the level of this enzyme by 20-50 times indicates the presence of viral hepatitis, as well as diseases accompanied by liver tissue necrosis.

The rate of AST depends on the age, sex and weight of the patient. His lifestyle also plays an important role. In the body of a healthy person, the amount of AST is insignificant, while in men the content of this enzyme in the blood is higher than in women;

• GTT. If the patient being examined is a woman, the norm of this enzyme is from 4 to 38 U / liter, and if a man is from 2 to 55 U / liter. An increase in GTT is observed in hepatitis of various etiology, cholestasis and alcohol poisoning;
• Bilirubin. This pigment substance is one of the components of bile, which is formed during the decomposition of hemoglobin. There are three types of bilirubin: general, direct, and indirect. A change in the level of this substance indicates the presence of a pathological process in the bile ducts. The norm of total bilirubin is 6-20.5 μmol / liter, direct - 3.4 μmol / liter, and indirect - from 3.5 to 18.5 μmol / liter. An increase in bilirubin levels indicates a problem in the biliary tract or liver damage to toxins. Sometimes an increase in bilirubin levels is a sign of diseases such as viral hepatitis, helminthiasis, and cirrhosis. Indicators of total and direct bilirubin also increase if a person has been following a low-calorie diet for a long time;
• Alkaline phosphatase. This enzyme of the bile ducts plays an essential role in the exchange of phosphorus and calcium, affecting the state of bone tissue. A large amount of alkaline phosphatase is found in the liver, intestinal mucosa and mammary glands. The rate of this enzyme depends on the age of the patient. In young people under the age of thirty, the alkaline phosphatase rate is 31–92 IU / liter, and in people over thirty years old - 38-117 IU / liter. Alkaline phosphatase is present in large quantities in the analyzes of children, which is a physiological norm.

An increase in alkaline phosphatase occurs with metabolic disorders in the body. An increase in this enzyme may indicate cholestasis, cirrhosis, or alcohol poisoning. Also, a slight increase in alkaline phosphatase is observed during pregnancy and after the onset of menopause. A decrease in the indicators of this enzyme below the norm indicates thyroid diseases;

• Albumin is a valuable transport protein in the human body that is produced by the liver. Its normal level is between 38 and 50 g / liter. Albumin decreases in tumors, cirrhosis and inflammatory processes in the liver. An increase in this substance is observed with a significant lack of fluid in the body, as well as with injuries and burns;
• Thymol test. This test is performed by adding a saturated solution of thymol to the blood serum. Using a special device, a laboratory specialist evaluates the degree of turbidity of the solution. The thymol test rate is in the range from 0 to 5 units. Exceeding these values occurs when protein synthesis is impaired and signals cirrhosis, connective tissue diseases and viral hepatitis. Thymol test allows you to make an accurate diagnosis at an early stage and start adequate treatment;
• Total protein. This term refers to the total concentration of albumin and globulin in the blood serum. It is the main component of protein metabolism in the human body.

Normally, total protein ranges from 65 to 86 g / liter. An increase in protein is observed with inflammation of the gallbladder and its ducts, hepatitis, cirrhosis, the appearance of helminths in the liver, as well as with burns. A decrease in total protein values can be the result of cancer, bleeding, or kidney disease.

Deciphering liver function tests does not take much time. Today it plays an essential role in the diagnosis of liver diseases. Thanks to modern laboratory methods, doctors have a unique opportunity to identify any abnormalities in the liver at an early stage.