Liver function tests

Indicators of uptake, conjugation and excretion of anionic compounds

Serum total (direct; indirect) bilirubin: normally less than 17 mmol/l in females and less than 23 mmol/l in males.

Plasma proteins synthesised by the liver

These include: Albumin

Vitamin K-dependent blood coagulation factors: II, VII, IX, X; proteins C and S Fibrinolysis proteins

Protease inhibitors: Alpha 1-antitrypsin, alpha 2-antiplasmin, antithrombin III

Caeruloplasmin

Alpha-fetoprotein

Iron storage and binding proteins

Acute phase proteins

Urine bilirubin/urobilinogen.

Serum bile acids: levels rise with impaired hepatocyte extraction from portal venous blood.

Tests reflecting hepatocellular damage

Aspartate and/or alanine aminotransferase: aminotransferases catalyse amino group transfer from aspartic acid or alanine to ketoglutaric acid to produce oxaloacetic acid and pyruvic acid, respectively. Alanine aminotransferase is a cytosolic enzyme that is relatively liver specific. Aspartate aminotransfer-ase has both cytosolic and mitochondrial isoenzymes and is also found in skeletal and cardiac muscles, the kidneys, brain, pancreas and in blood cells. An AST/ALT ratio greater than 2 is typical of alcoholic liver injury, while ALT>AST is found with viral hepatitis.

Glutathione-S-transferase.

Serum ferritin.

Vitamin B12.

Clearance tests.

Tests indicating bile flow obstruction

Alkaline phosphatase: this can originate from liver, bone, intestine and placenta. It is present in both the apical or canalicular domain of the hepatocyte plasma membrane and in the luminal domain of bile duct epithelium.

Gamma glutamyl transferase (GGT) is derived from both hepatocytes and biliary epithelium.

5' nucleotidase.

Leucine aminopeptidase.

Lipoprotein X.

Tests of synthetic function

Serum albumin: normally 35-50 g/l. Albumin has a half-life of 20 days and about 10 g is synthesised and secreted by the hepatocytes each day. The level correlates with prognosis in chronic liver disease.

Serum prealbumin.

Serum cholinesterase.

Lecithin-cholesterol acyltransferase.

Serum protein electrophoresis.

Prothrombin and partial thromboplastin time.

Serum ammonia: normally less than 1 mg/l.

n fil

Haem

Microsomal haem oxygenases Biliverdin

Cytosolic biliverdin reductase Bilirubin

Figure 11.2 Production of bilirubin

Techniques to measure liver blood flow

Parenchymal clearance techniques;

Reticuloendothelial clearance of radiolabelled colloidal particles; Indicator dilution techniques. The uses of liver function tests include the detection of liver disease, the placement of liver disease in specific diagnostic categories and following the progress of liver disease.

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