This presentation is aimed at primary care physicians. It covers the fundamentals of liver function tests, including the basic principles of interpretation, and the key patterns of abnormalities. The focus is on how to approach liver function tests in a primary care setting.
3. 'Traditional' Liver Function Test (LFT)
ALT: alanine transaminase (SGPT)
AST: aspartate transaminase (SGOT)
ALP: alkaline phosphatase
GGT: gamma Glutamyl Transferase
Albumin, bilirubin
Total protein, globulin
Known as LFT, but they're really not!
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4. Utility of LFTs
• Advantages
Sensitive, non-invasive method to screen for liver
dysfunction
Patterns of abnormal LFTs can help recognized type of
liver disorder
Easy way to follow the course of liver diseases
• Limitations
– Poor sensitivity and specificity
– Seldom leads to diagnosis
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6. Broad Principles
Contextualization
Normal
LFT interpretation must be contextualized for each
individual patient
Different labs have different ‘normal’ values
‘Abnormal’ values may be ‘normal’
Patterns
LFTs rarely provide specific diagnosis
Rather, suggests the general category of liver disorder
through the pattern of abnormal LFT
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7. Normal vs Abnormal
Normal
Abnormal
2 SD
Normal values = mean ± 2SD of normal population
Normal: 95% of normal, asymptomatic patients have
numbers in this range on a “bell shaped curve”
Abnormal: By definition, 2.5% of normal patients have lab
values either above or below the “normal” range
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12. Markers of Hepatocellular Damage
ALT & AST most frequently used
Released when hepatocytes damaged
Normal values:
ALT: 5 – 40 IU/L
AST: 8 – 20 IU/L
Patterns to note:
AST: ALT ratio
Level of elevation
Rate of decline
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13. ALT vs AST
ALT
Cytosol
Half life: 47H
Low concentration in
other tissues:
Skeletal muscle, kidney,
heart
More specific for liver
AST
Cytosol 20%,
mitochondria 80%
Half life: cytosol 17H,
mitochondria 87H
Other tissues:
heart, RBC, skeletal
muscle, kidneys,
pancreas, brain, lung
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21. Alkaline Phosphatase (ALP)
Main marker of cholestasis
Normal: 20-70 IU/L
Half life: 7 days
Sources:
Hepatocytes
Osteoblasts, gut, kidney, placenta
Biliary obstruction:
Raised levels due to induction of ALP synthesis
May not rise until 1-2 days later
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22. Raised ALP: Causes
Physiologic Causes
Age > 60 yrs
Children, adolescents
Pregnancy
Blood group O
Post meal (fatty meal)
Pathologic Causes
Intrahepatic cholestasis
Extrahepatic
cholestasis (bile duct
obstruction)
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27. Coagulation Factors
All synthesized in liver except Factor VIII
Mostly present in excess
Prothrombin Time (PT): Factors I, II, V, VII, IX, X
Half life: Factor VII – 6H (shortest)
Abnormalities only occur when liver's biosynthetic
ability substantially impaired
Common causes:
Vit K deficiency (malnutrition, malabsorption)
Warfarin
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28. Albumin
300 – 500 g in body fluid
Synthesis: 15 g/ day
Degradation: 4% daily
Half life: 19 – 21 days
Not reliable indicator of acute liver disease
Not specific
Depends on nutrition, volume status, vascular integrity,
catabolism, hormones, stool/ urine losses
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32. Bilirubin
Unconjugated Bilirubin
Indirect bilirubin
Normal: < 0.8 mg/ dL
(< 13.6 µmol/L)
Lipid soluble, water
insoluble
Bound to albumin in plasma
Not filtered by kidney →
not present in urine
Conjugated Bilirubin
Direct bilirubin
Normal: 0.3 – 1.0 mg/dL
(5.1 – 17.0 µmol/L)
Water soluble, lipid
insoluble
Excreted in bile
Filtered by glomerulus →
majority reabsorbed, small
amount excreted in urine
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33. Isolated Unconjugated Hyperbilirubinemia
Unconjugated bilirubin > 85% of total bilirubin
Increased production:
Haemolysis: rarely > 5 mg/dL (85 µmol/L)
Ineffective erythropoiesis: folate/ iron deficiency
Drugs: rifampicin, ribavirin
Resolution of hematoma
Defects in hepatic uptake or conjugation:
Gilbert's syndrome, Criggler – Najjar syndrome
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34. Conjugated Hyperbilirubinemia
Conjugated bilirubin > 50% total bilirubin
Cannot differentiate between obstructive &
parenchymal causes
Tea coloured urine + clay coloured stool: usually
cholestatic cause, although parenchymal cause
possible
Malignant obstruction usually higher values
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35. Delta Bilirubin
Conjugated bilirubin covalently bound to albumin
Important fraction of total bilirubin in patients with
cholestasis & hepatobiliary disease
Prolonged half life: 19 – 21 days (albumin)
Late recovery phase: all bilirubin may be in this form
Explains 2 enigmas in patients with raised
conjugated bilirubin:
CB declines slowly in patients who are recovering well
No bilirubinuria during recovery phase as delta bilirubin
not filtered by glomeruli
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36. Summary
Principles of LFTs:
Contextualization, Normal Values, Abnormal Patterns
Patterns of Abnormal LFTs
Hepatocellular injury: ALT, AST
AST: ALT ratio
Level of elevation
Rate of decline
Cholestasis: ALP, GGT
Biosynthetic function: PT, albumin
Bilirubin
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37. Conclusion
'LFT's are numerous & somewhat confusing
Have limited sensitivity & specificity
Not all liver ds have abnormal LFT
Not all normal LFTs have normal livers
Decrease in values may not mean improvement
What to do?
All abnormal LFTs should be investigated
LFTs must be contextualized for each patient
Refer when unsure
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