liver function test

the following document contains various diagnostic test for screening liver function. and interpretation of results, which may confirm the presence of a disease or disorder

1. LIVER FUNCTION TESTS

Liver is the largest organ in the body. It is located below the diaphragm in the right upper
quadrant of the abdominal cavity and extended approximately from the right 5
th
rib to the lower
border of the rib cage. The working cells of the liver are known as hepatocytes.

Major Metabolic Functions of the Liver:
 Synthetic Function
o Plasma proteins (albumin, globulins), cholesterol, triglycerides and lipoproteins
 Detoxification and excretion
o Ammonia to urea (urea cycle), bilirubin, cholesterol, drug metabolites
 Storage Function
o Vitamins A, D, E, K and B12
 Production of bile salts
o Helps in digestion.
Liver function tests:
Liver function tests, also known as liver chemistries, help determine the health of your liver
by measuring the levels of proteins, liver enzymes, and bilirubin in your blood.
 Noninvasive methods for screening of liver dysfunction.
 Help in identifying general types of disorder.
 Assess severity and allow prediction of outcome.
 Disease and treatment follow up.
Liver function test is often recommended in the following situations:
 To check for damage from liver infections, such as hepatitis B and hepatitis C.
 To monitor the side effects of certain medications known to affect the liver.
 To monitor the disease and how well a treatment is working.
 If patient is experiencing the symptoms of a liver disorder.
 If patient has certain medical conditions such as high triglycerides, diabetes, high blood
pressure, or anaemia.
 If patient is alcoholic.
 If patient has gallbladder disease.

LFTs are classified as:
 Liver protein test:
o Albumin levels.
o Globulin levels.
o Albumin to globulin ratio.
o Prothrombin time.
 Liver enzyme test:
o Alkaline phosphatase (ALP)
o Alanine aminotransferase (ALT)
o Aspartate aminotransferase (AST)

2. o g-glutamyl transferase (GGT)
 Bilirubin tests:
o Serum bilirubin.
o Urobilinogen.

Bilirubin tests:
Bilirubin
 A by-product of red blood cell breakdown
 It is the yellowish pigment observed in jaundice
 High bilirubin levels are observed in:
o Gallstones, acute and chronic hepatitis

1. Serum bilirubin levels:
o Normal: 0.2 – 0.8 mg/dL
o Unconjugated (indirect): 0.2 – 0.7 mg/dL
o Conjugated (direct): 0.1 – 0.4 mg/dL

If the plasma bilirubin levels exceed 1mg/dl, the condition is called
hyperbilirubinemia. Levels between 1 & 2 mg/dl are indicative of latent jaundice. When the
bilirubin level exceeds 2 mg/dl, it diffuses into tissues producing yellowish discoloration of
sclera, conjunctiva, skin & mucous membrane resulting in jaundice.
Van den Bergh test is a specific test for identification of increased serum bilirubin
levels.

2. Urobilinogen (UBG) and bile salts:
Urobilinogen is a colourless by-product of bilirubin reduction. It is formed in the intestines by
bacterial action on bilirubin.
 Most UBG is metabolized in the large intestine but a fraction is excreted in urine (less
than 4 mg/day)
 Normally bile salts are NOT present in urine
 Obstruction in the biliary passages causes:
o Leakage of bile salts into circulation
o Excretion in urine
 Sensitive indicator of
o hepatocellular dysfunction
o alcoholic liver damage.

Liver protein tests:

1. Serum Albumin:
 The most abundant protein synthesized by the liver.
 Normal serum levels: 3.5 – 5 g/dL.
 Synthesis depends on the extent of functioning liver cell mass.
 Longer half-life: 20 days.
 Its levels decrease in all chronic liver diseases.
 Methods of estimation:
o Dye binding method
o Immunoassay

3. o Chromatography
o Salt -fractionation
3. Serum Globulin:
 Normal serum levels: 2.5 – 3.5g/dL
 a and b-globulins mainly synthesized by the liver
 They constitute immunoglobulins (antibodies)
 High serum g-globulins are observed in chronic hepatitis and cirrhosis:
o IgG in autoimmune hepatitis
o IgA in alcoholic liver disease

4. Albumin to globulin (A/G) ratio:
 Normal A/G ratio: 1.2/1 – 1.5/1
 Globulin levels increase in hypoalbuminemia as a compensation.

5. Prothrombin time:
 Prothrombin: synthesized by the liver, a marker of liver function.
 Half-life: 6 hrs. (indicates the present function of the liver).
 PT is prolonged only when liver loses more than 80% of its reserve capacity. PT is
prolonged in severe parenchymal liver disease due to decreased synthesis of
prothrombin.
 Vitamin K deficiency also causes prolonged PT. Intake of vitamin K does not affect PT
in liver disease.
 If PT returns to normal after vitamin K injection it indicates that hepatocyte function
is good.


Liver enzyme tests:

1. Alkaline phosphatase (ALP)
 A non-specific marker of liver disease.
 A family of Zinc metalloid enzymes, with a serine at the active centre. The release
inorganic phosphate from various organic phosphates.
 In the liver it is found in microvilli of bile canaliculi and on the sinusoidal surface of the
hepatocytes.
 Normal levels – 41-133 IU/L
 Moderate elevation observed in:
o Infective hepatitis, alcoholic hepatitis and hepatocellular carcinoma
 High levels are observed in:
o Extrahepatic obstruction (obstructive jaundice) and intrahepatic cholestasis
 Very high levels are observed in:
o Bone diseases

2. Alanine aminotransferase (ALT)
 ALT or SGPT (serum glutamate pyruvate transaminase)
 ALT is a cytoplasmic enzyme.
 More liver-specific than AST
 Normal range (U/L): 7-56 IU/L.
 High serum levels

4. o acute hepatitis (300-1000U/L)
 Moderate elevation
o alcoholic hepatitis (100-300U/L)
 Minor elevation
o cirrhosis, hepatitis C and non-alcoholic steatohepatitis (NASH) (50-100U/L)
 Appears in plasma many days before clinical signs appear.
 A normal value does not always indicate absence of liver damage.
 Obese but otherwise normal individuals may have elevated ALT levels.

3. Aspartate aminotransferase (AST)
 AST or SGOT (serum glutamate oxaloacetate transaminase)
 A marker of hepatocellular damage
 Normal range: 10-45 U/L.
 AST is found in both cytoplasm & mitochondria
 AST/SGOT also reflects damage to the hepatic cells & is less specific for liver disease.
 It can also be released with heart, muscle & brain disorders.
 AST help diagnose various heart, muscle or brain disorders, such as a myocardial
infarct (heart attack).
 High serum levels are observed in:
o Chronic hepatitis, cirrhosis and liver cancer

4. Gamma-glutamyl transferase (GGT)
 This is a microsomal enzyme widely distributed in body tissues, including liver.
 Used for glutathione synthesis
 Measurement of γ - glutamyl transpeptidase (GGT) activity provides a sensitive index
to assess liver abnormality.
 The activity of this enzyme almost parallels that of transaminases in hepatic damage.
 Moderate elevation observed in:
o Infective hepatitis and prostate cancers
 GGT is increased in:
o alcoholics despite normal liver function tests
 Highly sensitive to detecting alcohol abuse.