N2i: Describe the interpretation of lab assessment of liver function (albumin, glucose, bilirubin, coag profile, ammonia)
Clinical blood biochemistry can give info re: states of patient’s liver
Divided into:
Enzymes of Hepatocyte Integrity
AST/ALT – < 40IU/L
- Enzymes of parenchymal cells
- Used to assess cellular injury
- ALT is more specific to liver tissue & less elevated with alcoholic hepatitis
- AST:ALT > 2:1 → strongly suggest ETOH aetiology, especially if ↑GGT
- ↑enzyme release with liver damage, but no correlation with disease severity
- Not useful at determining liver function
Enzymes of Cholestasis
ALKP 30 – 120IU/L
- Enzyme of cells lining bile ducts
- Non-specific (i.e. found in bone)
- ↑with biliary obstruction, ↑bone turnover (i.e. Paget’s disease)
GGT <50 IU/L
- Enzyme lining biliary tract
- Isolated ↑GGT = EtOH
- ↑with biliary obstruction
Synthetic Liver Function
Albumin – Normal 29 – 58g/L
- Protein synthesised exclusively by liver
- T ½ 20 days
- ∴not good indicator of acute hepatic dysfunction
- Can also ↓ with malnutrition
Coagulation factors – Normal INR <1.3, PT 9.5 – 13.5 secs
- All clotting factors except F VIII & vWF synthesised exclusively by liver
- Rapid turnover → ∴good indicators of liver function
- Must consider Vit K deficiency because liver disease will = ↓ ADEK absorption
BGL
- ↓with severe liver dysfunction
- Glycogen store, gluconeogenesis
Lipid profile
- Elevate TAGS & lipoprotein with abnormal liver metabolism
Detoxification & Excretory Function
Bilirubin <1.5mg/dL
- Breakdown product of heme metabolism
- Liver conjugates (H2O solubility) → excreted in bile
- Conjugated & unconjugated levels in bile & urine will indicate intrahepatic disease/post-hepatic obs
- Intrahepatic = ↓conjugated & ↑unconjugated plasma
- Post-hepatic = ↑conjugated, ↑urobilinogen
NH3 – Normal <50µmol/L
- Amino acid metabolism
- Converted to urea by liver
- ↑with liver failure
Other
- Test for specific causes of liver disease, including hepatitis serology, antimicrosomal antinuclear Ab, a-fetoprotein (hepatoma), Fe studies (haemochromatosis), ceruloplasmin (Wilson’s disease) & many others