Liver function tests
Encyclopedia
Liver function tests are groups of clinical biochemistry laboratory blood assays
designed to give information about the state of a patient's liver
. The parameters measured include PT/INR, aPTT, albumin, billirubin (direct and indirect) and others. According to some, liver transaminases (AST/ALT (SGOT/SGPT) are NOT liver function tests but are biomarkers of liver injury in a patient with some degree of intact liver function. Other sources include transaminases. Most liver disease
s cause only mild symptoms initially, but it is vital that these diseases be detected early. Hepatic (liver) involvement in some diseases can be of crucial importance. This testing is performed by a medical technologist
on a patient's serum or plasma
sample obtained by phlebotomy
. Some tests are associated with functionality (e.g., albumin); some with cellular integrity (e.g., transaminase
) and some with conditions linked to the biliary tract (gamma-glutamyl transferase and alkaline phosphatase
). Several biochemical tests are useful in the evaluation and management of patients with hepatic dysfunction. These tests can be used to (1) detect the presence of liver disease, (2) distinguish among different types of liver disorders, (3) gauge the extent of known liver damage, and (4) follow the response to treatment. Some or all of these measurements are also carried out (usually about twice a year for routine cases) on those individuals taking certain medications- anticonvulsants are a notable example- in order to ensure that the medications are not damaging the person's liver.
Albumin
is a protein made specifically by the liver, and can be measured cheaply and easily. It is the main constituent of total protein; the remaining fraction is called globulin (including the immunoglobulins). Albumin levels are decreased in chronic liver disease, such as cirrhosis. It is also decreased in nephrotic syndrome, where it is lost through the urine. Poor nutrition or states of impaired protein catabolism, such as in Ménétrier's disease
, may also lead to hypoalbuminaemia. The half-life of albumin is approximately 20 days. Albumin is not considered to be an especially useful marker of liver synthetic function; coagulation factors (see below) are much more sensitive
Alanine transaminase
(ALT), also called Serum Glutamic Pyruvate Transaminase
(SGPT) or Alanine aminotransferase (ALAT) is an enzyme
present in hepatocyte
s (liver cells). When a cell is damaged, it leaks this enzyme into the blood, where it is measured. ALT rises dramatically in acute liver damage, such as viral hepatitis
or paracetamol (acetaminophen) overdose
. Elevations are often measured in multiples of the upper limit of normal (ULN).
Aspartate transaminase
(AST) also called Serum Glutamic Oxaloacetic Transaminase (SGOT) or aspartate aminotransferase (ASAT) is similar to ALT in that it is another enzyme associated with liver parenchymal cells. It is raised in acute liver damage, but is also present in red blood cells, and cardiac and skeletal muscle and is therefore not specific to the liver. The ratio of AST to ALT
is sometimes useful in differentiating between causes of liver damage. Elevated AST levels are not specific for liver damage, and AST has also been used as a cardiac marker.
Alkaline phosphatase
(ALP) is an enzyme in the cells lining the biliary ducts of the liver. ALP levels in plasma will rise with large bile duct obstruction, intrahepatic cholestasis
or infiltrative diseases of the liver. ALP is also present in bone
and placenta
l tissue, so it is higher in growing children (as their bones are being remodelled) and elderly patients with Paget's disease
.
Bilirubin
is a breakdown product of heme
(a part of hemoglobin
in red blood cells). The liver is responsible for clearing the blood of bilirubin. It does this by the following mechanism: Bilirubin is taken up into hepatocytes, conjugated (modified to make it water-soluble), and secreted into the bile, which is excreted into the intestine.
Increased total bilirubin causes jaundice
, and can signal a number of problems:
The diagnosis is narrowed down further by looking at the levels of direct bilirubin.
Although reasonably specific to the liver and a more sensitive marker for cholestatic damage than ALP, Gamma glutamyl transpeptidase
(GGT) may be elevated with even minor, sub-clinical levels of liver dysfunction. It can also be helpful in identifying the cause of an isolated elevation in ALP. (GGT is raised in chronic alcohol toxicity).
is another test specific for cholestasis or damage to the intra or extrahepatic biliary system, and in some laboratories, is used as a substitute for GGT for ascertaining whether an elevated ALP is of biliary or extra-biliary origin.
factors. The international normalized ratio (INR) measures the speed of a particular pathway of coagulation, comparing it to normal. Increased levels of INR means that blood is taking more time than usual to coagulate or clot. The INR will be increased only if the liver is so damaged that synthesis of vitamin K
-dependent coagulation factors has been impaired; it is not a sensitive measure of liver function.
It is very important to normalize the INR before operating on people with liver problems (usually by transfusion with blood plasma containing the deficient factors) as they could bleed excessively.
Serum glucose
The liver's ability to produce glucose (gluconeogenesis
) is usually the last function to be lost in the setting of fulminant liver failure.
is an enzyme found in many body tissues, including the liver. Elevated levels of LDH may indicate liver damage.
Assay
An assay is a procedure in molecular biology for testing or measuring the activity of a drug or biochemical in an organism or organic sample. A quantitative assay may also measure the amount of a substance in a sample. Bioassays and immunoassays are among the many varieties of specialized...
designed to give information about the state of a patient's liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
. The parameters measured include PT/INR, aPTT, albumin, billirubin (direct and indirect) and others. According to some, liver transaminases (AST/ALT (SGOT/SGPT) are NOT liver function tests but are biomarkers of liver injury in a patient with some degree of intact liver function. Other sources include transaminases. Most liver disease
Liver disease
Liver disease is a broad term describing any single number of diseases affecting the liver.-Diseases:* Hepatitis, inflammation of the liver, caused mainly by various viruses but also by some poisons , autoimmunity or hereditary conditions...
s cause only mild symptoms initially, but it is vital that these diseases be detected early. Hepatic (liver) involvement in some diseases can be of crucial importance. This testing is performed by a medical technologist
Medical technologist
A Medical Laboratory Scientist is a healthcare professional who performs chemical, hematological, immunologic, microscopic, and bacteriological diagnostic analyses on body fluids such as blood, urine, sputum, stool, cerebrospinal fluid , peritoneal fluid, pericardial fluid, and synovial...
on a patient's serum or plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
sample obtained by phlebotomy
Venipuncture
In medicine, venepuncture, venopuncture or venipuncture is the process of obtaining intravenous access for the purpose of intravenous therapy or for blood sampling of venous blood. This procedure is performed by medical laboratory scientists, medical practitioners, some EMTs, paramedics,...
. Some tests are associated with functionality (e.g., albumin); some with cellular integrity (e.g., transaminase
Transaminase
In biochemistry, a transaminase or an aminotransferase is an enzyme that catalyzes a type of reaction between an amino acid and an α-keto acid. To be specific, this reaction involves removing the amino group from the amino acid, leaving behind an α-keto acid, and transferring it to the...
) and some with conditions linked to the biliary tract (gamma-glutamyl transferase and alkaline phosphatase
Alkaline phosphatase
Alkaline phosphatase is a hydrolase enzyme responsible for removing phosphate groups from many types of molecules, including nucleotides, proteins, and alkaloids. The process of removing the phosphate group is called dephosphorylation...
). Several biochemical tests are useful in the evaluation and management of patients with hepatic dysfunction. These tests can be used to (1) detect the presence of liver disease, (2) distinguish among different types of liver disorders, (3) gauge the extent of known liver damage, and (4) follow the response to treatment. Some or all of these measurements are also carried out (usually about twice a year for routine cases) on those individuals taking certain medications- anticonvulsants are a notable example- in order to ensure that the medications are not damaging the person's liver.
Albumin (Alb)
| Reference range Reference ranges for common blood tests Reference ranges for blood tests are sets of values used by a health professional to interpret a set of medical test results from blood samples.... |
| 3.5 to 5.3 g/dL |
Albumin
Albumin
Albumin refers generally to any protein that is water soluble, which is moderately soluble in concentrated salt solutions, and experiences heat denaturation. They are commonly found in blood plasma, and are unique to other blood proteins in that they are not glycosylated...
is a protein made specifically by the liver, and can be measured cheaply and easily. It is the main constituent of total protein; the remaining fraction is called globulin (including the immunoglobulins). Albumin levels are decreased in chronic liver disease, such as cirrhosis. It is also decreased in nephrotic syndrome, where it is lost through the urine. Poor nutrition or states of impaired protein catabolism, such as in Ménétrier's disease
Ménétrier's disease
Ménétrier disease , a disorder in which the gastric mucosal folds are enlarged , making the surface of the stomach look a bit like the brain gyri...
, may also lead to hypoalbuminaemia. The half-life of albumin is approximately 20 days. Albumin is not considered to be an especially useful marker of liver synthetic function; coagulation factors (see below) are much more sensitive
Alanine transaminase (ALT)
| Reference range |
| 9 to 52 IU/L |
Alanine transaminase
Alanine transaminase
Alanine transaminase or ALT is a transaminase enzyme . It is also called serum glutamic pyruvic transaminase or alanine aminotransferase ....
(ALT), also called Serum Glutamic Pyruvate Transaminase
Transaminase
In biochemistry, a transaminase or an aminotransferase is an enzyme that catalyzes a type of reaction between an amino acid and an α-keto acid. To be specific, this reaction involves removing the amino group from the amino acid, leaving behind an α-keto acid, and transferring it to the...
(SGPT) or Alanine aminotransferase (ALAT) is an enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
present in hepatocyte
Hepatocyte
A hepatocyte is a cell of the main tissue of the liver. Hepatocytes make up 70-80% of the liver's cytoplasmic mass.These cells are involved in:* Protein synthesis* Protein storage* Transformation of carbohydrates...
s (liver cells). When a cell is damaged, it leaks this enzyme into the blood, where it is measured. ALT rises dramatically in acute liver damage, such as viral hepatitis
Viral hepatitis
Viral hepatitis is liver inflammation due to a viral infection. It may present in acute or chronic forms. The most common causes of viral hepatitis are the five unrelated hepatotropic viruses Hepatitis A, Hepatitis B, Hepatitis C, Hepatitis D, and Hepatitis E...
or paracetamol (acetaminophen) overdose
Paracetamol toxicity
Paracetamol toxicity is caused by excessive use or overdose of the analgesic drug paracetamol . Mainly causing liver injury, paracetamol toxicity is one of the most common causes of poisoning worldwide...
. Elevations are often measured in multiples of the upper limit of normal (ULN).
Aspartate transaminase (AST)
| Reference range |
| 10 to 35 IU/L |
Aspartate transaminase
Aspartate transaminase
Aspartate transaminase , also called aspartate aminotransferase or serum glutamic oxaloacetic transaminase , is a pyridoxal phosphate -dependent transaminase enzyme . AST catalyzes the reversible transfer of an α-amino group between aspartate and glutamate and, as such, is an important enzyme in...
(AST) also called Serum Glutamic Oxaloacetic Transaminase (SGOT) or aspartate aminotransferase (ASAT) is similar to ALT in that it is another enzyme associated with liver parenchymal cells. It is raised in acute liver damage, but is also present in red blood cells, and cardiac and skeletal muscle and is therefore not specific to the liver. The ratio of AST to ALT
AST/ALT ratio
The aspartate aminotransferase/alanine aminotransferase ratio is sometimes useful in differentiating between causes of liver damage .-Interpretation:...
is sometimes useful in differentiating between causes of liver damage. Elevated AST levels are not specific for liver damage, and AST has also been used as a cardiac marker.
Alkaline phosphatase (ALP)
| Reference range |
| 30 to 120 IU/L |
Alkaline phosphatase
Alkaline phosphatase
Alkaline phosphatase is a hydrolase enzyme responsible for removing phosphate groups from many types of molecules, including nucleotides, proteins, and alkaloids. The process of removing the phosphate group is called dephosphorylation...
(ALP) is an enzyme in the cells lining the biliary ducts of the liver. ALP levels in plasma will rise with large bile duct obstruction, intrahepatic cholestasis
Cholestasis
In medicine, cholestasis is a condition where bile cannot flow from the liver to the duodenum. The two basic distinctions are an obstructive type of cholestasis where there is a mechanical blockage in the duct system such as can occur from a gallstone or malignancy and metabolic types of...
or infiltrative diseases of the liver. ALP is also present in bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
and placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l tissue, so it is higher in growing children (as their bones are being remodelled) and elderly patients with Paget's disease
Paget's disease of bone
Paget's disease is a chronic disorder that can result in enlarged and misshapen bones. The excessive breakdown and formation of bone tissue causes affected bone to weaken, resulting in pain, misshapen bones, fractures, and arthritis in the joints near the affected bones...
.
Total bilirubin (TBIL)
| Reference range |
| 0.2–1.2 mg/dL |
Bilirubin
Bilirubin
Bilirubin is the yellow breakdown product of normal heme catabolism. Heme is found in hemoglobin, a principal component of red blood cells. Bilirubin is excreted in bile and urine, and elevated levels may indicate certain diseases...
is a breakdown product of heme
Heme
A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are...
(a part of hemoglobin
Hemoglobin
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...
in red blood cells). The liver is responsible for clearing the blood of bilirubin. It does this by the following mechanism: Bilirubin is taken up into hepatocytes, conjugated (modified to make it water-soluble), and secreted into the bile, which is excreted into the intestine.
Increased total bilirubin causes jaundice
Jaundice
Jaundice is a yellowish pigmentation of the skin, the conjunctival membranes over the sclerae , and other mucous membranes caused by hyperbilirubinemia . This hyperbilirubinemia subsequently causes increased levels of bilirubin in the extracellular fluid...
, and can signal a number of problems:
- 1. Prehepatic: Increased bilirubin production. This can be due to a number of causes, including hemolytic anemias and internal hemorrhage.
- 2. Hepatic: Problems with the liver, which are reflected as deficiencies in bilirubin metabolism (e.g., reduced hepatocyte uptake, impaired conjugation of bilirubin, and reduced hepatocyte secretion of bilirubin). Some examples would be cirrhosis and viral hepatitis.
- 3. Posthepatic: Obstruction of the bile ducts, reflected as deficiencies in bilirubin excretion. (Obstruction can be located either within the liver or in the bile ductBile ductA bile duct is any of a number of long tube-like structures that carry bile.Bile, required for the digestion of food, is excreted by the liver into passages that carry bile toward the hepatic duct, which joins with the cystic duct to form the common bile duct, which opens into the intestine.The...
).
Direct bilirubin (Conjugated Bilirubin)
| Reference range |
| 0.1–0.4 mg/dL |
The diagnosis is narrowed down further by looking at the levels of direct bilirubin.
- If direct (i.e. conjugated) bilirubin is normal, then the problem is an excess of unconjugated bilirubin, and the location of the problem is upstream of bilirubin excretion. Hemolysis, viral hepatitis, or cirrhosis can be suspected.
- If direct bilirubin is elevated, then the liver is conjugating bilirubin normally, but is not able to excrete it. Bile ductBile ductA bile duct is any of a number of long tube-like structures that carry bile.Bile, required for the digestion of food, is excreted by the liver into passages that carry bile toward the hepatic duct, which joins with the cystic duct to form the common bile duct, which opens into the intestine.The...
obstruction by gallstones or cancer should be suspected.
Gamma glutamyl transpeptidase (GGT)
| Reference range |
| 0 to 42 IU/L |
Although reasonably specific to the liver and a more sensitive marker for cholestatic damage than ALP, Gamma glutamyl transpeptidase
Gamma glutamyl transpeptidase
Gamma-glutamyltransferase or gamma-glutamyl transpeptidase is an enzyme that transfers gamma-glutamyl functional groups...
(GGT) may be elevated with even minor, sub-clinical levels of liver dysfunction. It can also be helpful in identifying the cause of an isolated elevation in ALP. (GGT is raised in chronic alcohol toxicity).
5' Nucleotidase (5'NTD)
5' NucleotidaseNucleotidase
A nucleotidase is a hydrolytic enzyme that catalyzes the hydrolysis of a nucleotide into a nucleoside and a phosphate. For example, they convert adenosine monophosphate to adenosine, and guanosine monophosphate to guanosine....
is another test specific for cholestasis or damage to the intra or extrahepatic biliary system, and in some laboratories, is used as a substitute for GGT for ascertaining whether an elevated ALP is of biliary or extra-biliary origin.
Coagulation test (e.g., INR)
The liver is responsible for the production of coagulationCoagulation
Coagulation is a complex process by which blood forms clots. It is an important part of hemostasis, the cessation of blood loss from a damaged vessel, wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel...
factors. The international normalized ratio (INR) measures the speed of a particular pathway of coagulation, comparing it to normal. Increased levels of INR means that blood is taking more time than usual to coagulate or clot. The INR will be increased only if the liver is so damaged that synthesis of vitamin K
Vitamin K
Vitamin K is a group of structurally similar, fat soluble vitamins that are needed for the posttranslational modification of certain proteins required for blood coagulation and in metabolic pathways in bone and other tissue. They are 2-methyl-1,4-naphthoquinone derivatives...
-dependent coagulation factors has been impaired; it is not a sensitive measure of liver function.
It is very important to normalize the INR before operating on people with liver problems (usually by transfusion with blood plasma containing the deficient factors) as they could bleed excessively.
Serum glucoseGlucoseGlucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
(BG, Glu)
The liver's ability to produce glucose (gluconeogenesisGluconeogenesis
Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids....
) is usually the last function to be lost in the setting of fulminant liver failure.
Lactate dehydrogenase (LDH)
Lactate dehydrogenaseLactate dehydrogenase
Lactate dehydrogenase is an enzyme present in a wide variety of organisms, including plants and animals.Lactate dehydrogenases exist in four distinct enzyme classes. Two of them are cytochrome c-dependent enzymes, each acting on either D-lactate or L-lactate...
is an enzyme found in many body tissues, including the liver. Elevated levels of LDH may indicate liver damage.
See also
- Reference ranges for blood tests
- Elevated transaminasesElevated transaminasesIn medicine, the presence of elevated transaminases, commonly the transaminases alanine transaminase and aspartate transaminase , may be an indicator of liver damage...
- Liver disorders and liver diseases.
External links
- Overview at Mayo ClinicMayo ClinicMayo Clinic is a not-for-profit medical practice and medical research group specializing in treating difficult patients . Patients are referred to Mayo Clinic from across the U.S. and the world, and it is known for innovative and effective treatments. Mayo Clinic is known for being at the top of...
- Abnormal Liver Function Tests
- Overview of liver enzymes