Part One: Tests that detect injury to hepatocytes (serum enzyme tests)
Primarily marker of hepatocellular injury (most sensitive, more specific than AST),
Liver cell death —> leaks in blood.
No correlation with extent of damage.
A) High ALT (>15-20 times)
Ischaemia (Much Higher) (Shock, hypotension, CCF, comes down rapidly)
Viral hepatitis, Autoimmune
Drug toxicity (PCM), Severe toxic hepatitis
Acute budd chiary syndrome
B) Moderate ALT (5-15 times)
Liver – Chronic Liver disease (eg Chronic hepatitis)
Cholestasis (with ALP, GGT)
Cardiac –Severe hepatic congestion in cardiac failure
Other: Muscle injury, Kidney injury
C) Slight increase in ALT (<5 times)
Liver: Neonatal hepatitis
Alpha1-antitrypsin deficiency, Wilson’s disease
Infection: Infectious mononucleosis
Drugs: Almost any drug. (ATT, AED, Antibiotics, NASAIDS), PCM therapeutic doses,
D) False low ALT: Dialysis, Pyridoxine deficiency
Note: Drugs more likely to cause an asymptomatic abnormality in liver function.
Origin: Liver, cardiac, skeletal muscle, kidney, brain, pancreas.
Reflects damage to the hepatic cell , but less specific for liver disease.
A) High AST (>20 times)
Ischaemic liver injury(Shock, hypoperfusion)
Acute viral hepatitis
Drug induced hepatic injury
B) Moderate AST (15-20 times)
Infection: (Infectious mononucleosis)
Liver: (Alcoholic cirrhosis)
C) Mild AST (5-10 times)
Liver: Chronic hepatitis Specially alcoholic
Skeletal muscle: DMD, Dermatomyositis, Infl. B calf muscle myositis
D) Even milder AST (<5 times)
Blood: Haemolytic anaemia, haemolysis
Liver; Fatty liver, Metastatic hepatic tumour
Other: PE, Acute pancreatitis, Strenuous exercise
Drugs: Almost any drug
Ratios between AST and ALT are useful in differentials
AST: ALT =1 (Equal rise)
Ischaemia ( Shock, hypoxia, hypoperfsion injury)
AST: ALT <1 ( More ALT, specific for Hepatocellular damage )
PCM poisoning with hepatocellular necrosis
Viral hepatitis, toxic hepatitis, Cholestatic hepatitis
Chronic active hepatitis, NASH
AST: ALT >2.5 (More AST)
Wilsons disease, cirrhosis
Bile duct obstruction, Tumours
(Adults:Alcoholic liver disease)
WHY: Depletion of vitamin B6 in chronic alcoholics. ALT and AST both use B6 as a coenzyme, but the synthesis of ALT is more strongly inhibited by pyridoxine deficiency than is the synthesis of AST. Alcohol also causes mitochondrial injury, which releases the mitochondrial isoenzyme of AST.
Slight AST or ALT elevations (within 1.5 × normal) do not necessarily indicate liver disease.
WHY: unlike the values in many other biochemical tests, AST and ALT levels do not follow a normal bellshaped distribution in the population.
They have a skewed distribution characterized by a long “tail” at the high end of the scale.
3. Alkaline Phosphatase (ALP)