Write commonly done liver function test with their interpretation.

1.      Test for hepatocellular damage:

a.      ALT (alanine transaminase)

b.      AST (aspartate transaminase)

c.       ᵞ-GT  (gamma glutamyl transferase)

These enzyme are present within hepatocytes where they perform specific functions. Damage to hepatocytes or increased membrane permeability of hepatocytes due to inflammatory assault causes release of these enzymes into blood. As a result their concentration in plasma increase and their plasma concentration ten times normal are highly specific for liver damage.

2.      Test for cholestasis.

a.      ALP (alkaline phosphatase)

b.      γ-GT (gamma glutamyl transferase)

ALP is the most important indicator of cholestasis.

3.      Test for synthetic function:

a.      Serum total protein concentration

b.      Serum albumin concentration

c.       Serum albumin globulin ratio

d.      Prothrombin time

Synthesis of albumin exclusively happens in liver, but globulin is partly synthesized in plasma cells as well. So in hepatic dysfunction serum concentration of total protein and albumin decreases markedly. But serum globulin concentration is little affected leading to alteration of albumin to globulin ratio.

The clotting factors involved with the Prothrombin time are factor I, II, V, VII and X. all are produced by liver and for synthesis of factor II, VII, IX and X vitamin K is needed. Prolonged Prothrombin time indicates the deficiency of concerned clotting factors due to hepatic dysfunction or vitamin K deficiency. In hepatic dysfunction, Prothrombin time is found prolonged even 18-20 hours after vitamin K injection.

Half life of albumin is about 20 days and that of Prothrombin is hours to days, so Prothrombin time rather than serum albumin or total protein is more sensitive and early marker of the impaired synthetic function of liver.

4. Test for excretory and conjugating function:

Done by the measurement of serum bilirubin concentration.

Bilirubin is produced in reticulo-endothelial cells and transported in blodd along with albumin. Hepatocytes take up biliruin from blood followed by its conjugation within the cells and then excrete in bile. Failure of hepatic conjugation and excretion of conjugated bilirubin in bile leads to increase serum bilirubin concentration and jaundice.

5. Test for metabolic function of liver:

Done by galactose tolerance test.

Galactose after absorption goes to liver and mostly converted to glucose with a very little amount of galactose excreted in urine. In hepatic dysfunction following a test dose of galactose given orally more than expected amount of galactose appears in urine.