Liver Function Tests

Liver Function Tests.

Liver cells or hepatocytes and bile duct cells ( cholangiocytes ) originate from hepatoblasts as common precursors. The biliary tree continues throughout human fetal life and at the time of birth the most peripheral branches of the portal veins are still surrounded by ductal plates; these require 4 more weeks to develop into definitive portal ducts. The liver constitutes 5% of body weight at birth but only 2% in an adult..

The liver is unusual in that it has a double blood supply ; the right and left hepatic arteries carry oxygenated blood to the liver, and the portal vein carries venous blood from the GI tract to the liver. The products of the hepatobiliary system are released by 2 different paths: through the hepatic vein and through the biliary system back into the intestine..

Liver Function:” metabolic and synthetic activities”.

Metabolic function:. Carbohydrate metabolism: Stores excess carbohydrate (complex form as glycogen), readily hydrolysed (metabolic end product”glucose ”) during fasting. The liver regulates serum glucose levels, so blood glucose to be monitored when liver dysfunction is suspected..

Protein metabolism: a α-fetoprotein , which is the dominant fetal protein during early gestation. Synthesis of albumin appears at approximately the 7th-8th wk in the human fetus. By the 3rd-4th mo of gestation, the fetal liver is able to produce fibrinogen, transferrin, and low-density lipoproteins ..

Lipid metabolism: Hepatic metabolic processes for lipids and lipoproteins are dominantly fatty acid oxidation and ketogensis . -When the glucose supply is limited, ketone body production from endogenous fatty acids can provide energy as an alternative fuel for brain metabolism. -When carbohydrates are in excess, the liver produces triglycerides . * SO liver immaturity or disease affects lipid concentrations and lipoproteins ..

” Hepatic Excretory Function”. Hepatic excretory function and bile flow are closely related to hepatic bile acid excretion and enterohepatic recirculation. Enterohepatic circulation refers to the circulation of biliary acids, bilirubin, drugs or other substances from the liver to the bile, followed by entry into the small intestine, absorption by the enterocyte, to assist in fat digestion and absorption, converted into stercobilinogen (by the intestinal bacterial flora), and transport back to the liver, re-excreted into the bile or execreted by kidney as urobilinogen ..

** production and storage of essential nutrients, excretion of bile, and establishment of processes of elimination (irreversible removal). Your liver is the organ below the lungs that act like a filter for the blood . Chemicals and impurities, including drugs and medications are filtered by the liver..

For a patient with suspected liver disease, evaluation addresses the following issues in sequence:.

Evaluation of Patients with Possible Liver Dysfunction.

Any single biochemical assay provides limited information, which must be placed in the context of the entire clinical picture..

Liver function tests ( LFTs or LFs), also referred to as a hepatic panel, are groups of blood tests that provide information about the state of a patient's liver . These tests include liver enzymes (ALT&AST), prothrombin time (PT/INR), aPTT , albumin, bilirubin (direct and indirect), and others..

LIVER FUNCTION TESTS:. Better term is liver biochemical tests. These tests are complementary, provide an estimation of synthetic and excretory functions , and might suggest the nature of the disturbance (inflammation or cholestasis)..

serum aminotransferase:. Alanine aminotransferase (ALT, serum glutamate pyruvate transaminase) is liver specific , whereas aspartate aminotransferase ( AST,serum glutamic- oxaloacetic transaminase) is derived from other organs in addition to the liver. Marked increase in serum aminotransferase levels reflects acute liver cell injury (parenchymal disease) . e.g. by viral hepatitis, drug- or toxin-induced liver disease, shock( hypoperfusion ), hypoxemia..

Serum Albumin & Total proteins:. **Serum albumin and protein levels reflect hepatic synthetic function. Hypoalbuminemia caused by depressed synthesis which can complicate severe liver disease and serve as a prognostic factor . Common causes of ↓s . proteins: renal disease, liver disease, protein losing enteropathy , malnutriotion , chronic inflammatory disease..

Prothrombin time:. Clotting factors that are synthesized by liver include: factor V and of the vitamin K–dependent factors (II, VII, IX, and X). Prolonged PT and INR can occur in patients with severe liver disease or fulminant hepatic failure(persistently low PTT). PT is part of MELD score: Model for End Stage Liver Disease ( Evaluating priority for liver transplantation)..

Serum Bilirubin ( Total & Direct). Fractionation of the total serum bilirubin level into conjugated and unconjugated bilirubin fractions helps to distinguish between elevations caused by processes such as hemolysis and those caused by hepatic dysfunction..

Serum Bilirubin ( Total & Direct). A predominant elevation in the conjugated bilirubin level provides a relatively sensitive index of hepatocellular disease or hepatic excretory dysfunction. Cholestasis (obstructive disease) involves regurgitation of bile components into serum; the serum levels of total and conjugated bilirubin and serum bile acids are elevated..

Alkaline Phasphatase (AP) & γ- glutamyl transpeptidase (GGT).

γ- glutamyl transpeptidase (GGT) is an enzyme that is found in many organs throughout the body, with the highest concentrations found in the liver . It plays a significant role in helping the liver metabolize drugs and other toxins. γ- glutamyl transpeptidase are increased in cholestatic conditions and may be more specific for hepatobiliary disease..

Elevations in serum AP and γ- glutamyl transpeptidase levels are sensitive indicators of obstruction or inflammation of the biliary tract..

Others:. Serum ammonia: Interpretation of serum ammonia values must be carried out with caution because of variability in their physiologic determinants Immunogloblins: an increase in immunoglobulin levels reflects an immunologic response to injury..

The ALT and AST tests measure enzymes that your liver releases in response to damage or disease (parenchymal disease) . The albumin test measures how well the liver creates albumin (synthetic function) , while the bilirubin test measures how well it disposes of bilirubin( execretory function) . ALP & γ- glutamyl transpeptidase (GGT) can be used to evaluate the bile duct system of the liver ..

Clinical Interpretation of LFT :. Biochemical alterations include hypoglycemia (metabolic impairment) , hyperammonemia (encephalopathy) , continued hyperbilirubinemia (jaundice) , marked hypoalbuminemia (edema/ascites) , or a prolonged PT or INR that is unresponsive to parenteral administration of vitamin K (bleeding tendency) ..

Liver Function Tests Liver chemistry test ALT AST Bilirubin ALP Albumin GGT Bile acids 5' -nucleotidase LDH Clinical implication of abnormality Hepatocellular damage Hepatocellular damage Cholestasis, impair conjugation, or biliary obstruction Cholestasis, infiltrative disease, or biliary obstruction Synthetic function Synthetic function Cholestasis or biliary obstruction Cholestasis or biliary obstruction Cholestasis or biliary obstruction Hepatocellular damage, not specific.