Measurement

Significance

Reference range

Alanine Transaminase (ALT)

or SGPT

Alanine transaminase (ALT), also called Serum Glutamic Pyruvate Transaminase (SGPT) or Alanine aminotransferase (ALAT) is an enzyme present in hepatocytes (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).

5 to 40 IU/L

     Aspartate

 Transaminase (AST) 

    or SGOT

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.

10 to 40 IU/L

  Alkaline Phosphatase      (AlP)

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 placental tissue, so it is higher in growing children (as their bones are being remodelled) and elderly patients with Paget's disease.

  30 to 120

     IU/L

    Total bilirubin (TBIL)

Bilirubin is a breakdown product of heme (a part of haemoglobin 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:

• 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 duct.)

2 – 14 μmol/L

  Direct bilirubin

(Conjugated bilirubin)

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 duct obstruction by gallstones or cancer should be suspected.

  0 – 4 μmol/L

 Gamma glutamyl  transpeptidase (GGT)

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 alcohol toxicity (acute and chronic). In some laboratories, GGT is not part of the standard LFTs and must be specifically requested.

0 to 51 IU/L