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
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10.5-13.0 sec
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bilirubin |
0.2-1.0 mg/dl
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glucose |
Tests of Biliary Obstruction
test serum bilirubin |
normal values 0.2-1.0 mg/dl |
causes of abnormal results
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serum alkaline phosphatase |
56-176 U/L
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gamma glutamyl transpeptidase |
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Tests of Hepatocellular Damage (Hepatitic)
test aspartate amino-transferase (AST) |
normal values 10-30 U/L |
causes of abnormal results
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alanine amino- |
5-30 U/L
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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.