Liver Chemistries - Interpretation of LFTs



R-value: Serum (ALT/ULN ALT) / (Alk phos/ULN ALP)

 • R > 5: Hepatocellular 

	- Check Acute viral hepatitis serologies, HCV RNA

 • R 2-5: Mixed

	- Check Acute viral hepatitis serologies, HCV RNA

 • R < 2: Cholestasis / Obstructive

	- Check Obtain imaging studies



Imperative to Identify Acute Liver Failure (ALF):

 • Liver injury < 26 weeks

 • INR > 1.5

 • Encephalopathy



Cellular Destruction: Hepatocellular Level

 • AST: Less specific to liver than ALT

 • ALT: Specific to liver than AST

 • GGT:

	- Specific to liver

	- Assists in liver specificity to elevated ALP

 • AST/ALT > ALP: Typical of hepatocellular injury

 • Bilirubin - +/- elevation



Obstruction: Cholestasis

 • ALP - Surface of bile duct epithelia

	- Cholestasis/Bile salts augment synthesis of ALP

	- Due to synthesis - rises later

	- Half life: 1 week

 • Direct bilirubin: ↑

 • AST: ↑

 • ALT: ↑

 • GGT/5-NT: ↑

 • ALP > AST/ALT: typical of cholestatic disease

 • If ALP ↑: Check GGT & 5-nucleotidase (5-NT)

	- If both are normal - ALP is from extrahepatic source



Production:

 • Albumin

 • Coagulation factors: PT/INR



Infiltrative - The liver is invaded or replaced by non-hepatic substances, such as neoplasm or amyloid:

 • Elevation of ALP

 • Near normal AST/ALT



AST:ALT Ratios:

 • Alcoholic liver disease: > 2

 • NASH, Chronic viral hepatitis: < 1

 • Cirrhosis: > 1

 • Acute muscle injury: > 3

 • Chronic muscle injury: ~ 1



Nonhepatic Source of Liver Enzyme Elevation:

 • Bilirubin: RBC (hemolysis, bleeding, hematoma)

 • AST: Skeletal muscle, cardiac muscle, RBC, Kidney, Brain

 • ALT: Skeletal muscle, Cardiac muscle, Kidneys

 • LDH: Heart, RBC (hemolysis)

 • ALP: Bone, First trimester placenta, kidneys, intestines, White blood cells



Unconjugated Bili > 90% of Total Bili Etiology:

 • Gilbert's syndrome

 • Hemolysis



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