Unless liver tests are carefully selected, good prognosis cannot be expected.
Tests used to initially evaluate liver disease can be categorized as two groups: (1) indicating injury, such as release of intracellular enzymes; and (2) measuring or representing actual function.
credit: Blood Test Careme
As major functions, the liver clears, biotransforms, and detoxifies toxic metabolites and exogenous compounds; synthesizes and exports various plasma proteins; and metabolizes carbohydrates, amino acids, and lipids.
When patients have specific diseases, although some of these liver functions may be remarkably impaired, others are not completely affected. Liver tests should be carefully selected and interpreted based on the total clinical situation.
1. Serum Enzyme Tests
The levels of hepatic enzymes found in plasma represents hepatocyte turnover or injury.
When cells get injured or die, phospholipases are activated to create holes in the plasma membrane, thereby increasing the release of intracellular contents.
2. Tests Based on Clearance of Metabolites and Drugs
The liver mainly removes various metabolites and toxins from the blood.
When patients have liver disease, metabolites and toxins may be properly removed because parenchymal cells are lost, bile secretion is decreased, bile duct is obstructed, cellular uptake or metabolism is decreased, or hepatic blood flow is decreased.
In the case that a metabolite (e.g., bilirubin) is produced at a constant rate, its serum level can serve for an adequate indicator of liver function. The clearance rate from plasma of certain drugs may be similarly interpreted.
Hyperbilirubinemia is a typical sign of diseases that includes generalized liver disease, inherited disorders of bilirubin metabolism, and nonhepatic conditions.
Higher bilirubin levels correlate with a poorer prognosis in acute alcoholic hepatitis, fulminant hepatic failure, primary biliary cirrhosis, and most forms of chronic liver disease.
Ammonia is a byproduct of amino acid metabolism. The liver removes ammonia from blood, converts it into urea in the Krebs-Henseleit cycle, and excretes it through the kidneys.
When patients have portosystemic shunting, severe hepatic dysfunction (e.g., fulminant hepatic failure), or defects in urea cycle metabolism, ammonia levels rise.
3. Tests Reflecting Hepatic Synthetic Function
3-1. Coagulation Tests
Coagulation tests measure patients' blood clotting ability and the amount of time it takes.
Diseases that cause coagulation problems include liver disease, thrombophilia (excessive clotting), and hemophilia (impairment of clotting inability).
3-2. Prothrombin Time
The prothrombin time represents the plasma concentrations of prothrombin and fibrinogen.
When patients have vitamin K deficiency, liver disease, or both, the prothrombin time will prolong.
Only the liver can produce albumin. Its plasma concentration represents the balance between its synthetic rate and its plasma half-life (about 21 days).
The synthetic rate of albumin varies depending on the patients' nutritional state, thyroid and glucocorticoid hormone levels, plasma colloid osmotic pressure, exposure to hepatotoxins (e.g., alcohol), and presence of systemic disorders or liver disease.