Liver Lab Investigations

Liver function tests rely on indirect measures of the cause or severity of liver disease. As the liver has a large reserve capacity, function tests can remain relatively normal until dysfunction is severe.

 

 

 

 

 

 

 

Tests of Liver Function


test

serum albumin

normal values

3.5-5.5 mg/dl

35-45 mg/L

causes of abnormal results

  • decreased synthetic capacity
  • protein malnutrition
  • increased protein loss
  • increased ECF volume

prothrombin time

10.5-13.0 sec

 

  • decreased synthetic capacity (esp F II and III)
  • vitamin K deficiency
  • consumptive coagulopathy

bilirubin

0.2-1.0 mg/dl
3.4-17.1 mol/L

 

  • hemolysis
  • diffuse liver disease
  • cholestasis
  • extrahepatic bile duct obstruction
  • congenital disorders of bilirubin metabolism

glucose

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Tests of Biliary Obstruction


test

serum bilirubin

normal values

0.2-1.0 mg/dl
3.4-17.1 mol/L

causes of abnormal results

  • hemolysis
  • diffuse liver disease
  • cholestasis
  • extrahepatic bile duct obstruction
  • congenital disorders of bilirubin metabolism

serum alkaline phosphatase

56-176 U/L

 

  • bile duct obstruction
  • cholestasis
  • infiltrative liver disease
  • bone destruction/remodeling
  • pregnancy

gamma glutamyl transpeptidase

 
  • inducible enzyme; not normally useful
  • indication: isolated elevated AlkPhos; can distinguish liver from bone
  • bile duct obstruction or cholestasis
  • alcohol and other drugs: neither sensitive nor specific
  • infiltrative liver disease
  • bone destruction/remodeling
  • brussel sprouts
  • pregnancy (from placenta)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Tests of Hepatocellular Damage (Hepatitic)


test

aspartate amino-transferase (AST)

normal values

10-30 U/L

causes of abnormal results

  • hepatocellular necrosis
  • cardiac or skeletal muscle necrosis
  • brain

alanine amino-
transferase (ALT)

5-30 U/L

 

  • hepatocellular necrosis (more specific)
  • cardiac or skeletal muscle necrosis
  • brain

 

 

 

 

 

 

 

 

 

The ratio of AST/ALT is 0.8 in most normal people. A ratio of 1-2 can be caused by cirrhosis or NASH/NAFLD; while a ratio of over 2 suggests alcohol damage.

 

Transaminases over 1000 suggest acute hepatitis, and can be caused by toxins, dugs, alcohol, hepatitis A or B, ischemia, shock, or Wilson's disease.

 

 

Platelets: low platelet counts can result from portal hypertension and splenic sequestration. Thrombopoietin is also produced in the liver and can lead to thrombocytopenia.

 

Creatine is created by the liver. A low creatinine can suggest advanced liver disease.

 

 

Background information of Tests

 

Because of the short half-life (hours) of factors II and III, prothromin time is a useful daily marker of liver function. Serum half-life of albumin is 14-20 days.

 

Other quantitative tests of liver function include indo-cyanine green clearance, galactose elimination, aminopyrine breath test, antipyrine clearance, and caffeine clearance, but they are currently only used for research.

Serum bilirubin levels represent the balance of bilirubin production and conjugation and excretion into bile.

Cholestasis causes retention of bile acids in the liver, leading to solubilization of plasma membrane enzymes such as alkaline phosphatase, γ-glutamyl transpeptidase, or 5-'nucleotidase.

 

AST and ALT are present in large quantities in hepatocytes and are released after injury or death of liver cells. One exception is with severe alcoholic hepatitis, which can lead to deficiency of pyridoxal 5'-phosphate. High aminotransferase levels can be seen in viral or toxic causes, or less frequently, in bile duct obstruction. Isolated asymptomatic elevations of ALT and AST may have non-alcoholic fatty liver disease caused by obesity, insulin resistance, or hyperlipidemia, alcohol-induced liver disease, hemochromatosis, or chronic viral hepatitis.

 

Serum bilirubin is most commonly measured using the van den Bergh reaction, which combines bilirubin with diazotized sulfanilic acid to form a coloured compound. Both conjugated and unconjugated bilirubin can be measured, using direct-reacting and indirect-reacting, respectively.