Liver Function Tests (LFTs)

• Liver function tests (LFTs) are biochemical investigations assessing the liver's capacity to perform its functions.
• LFTs aid in detecting liver disease, distinguishing liver disorder types, gauging disease extent, and monitoring treatment response.

Functions of the Liver

• Liver functions include carbohydrate, fat, and protein metabolism.
• The liver is involved in gluconeogenesis, glycogen synthesis/breakdown, and fatty acid/cholesterol synthesis.
• It synthesizes plasma proteins, some coagulation factors, and urea.
• The liver participates in hormone metabolism, drug/foreign compound processing, and bilirubin excretion.
• Storage functions include glycogen, vitamins A and B12, and iron.

Liver Function Tests

• Alanine transaminase (ALT) assists in converting proteins into energy for liver cells, increasing when the liver is damaged.
• Aspartate transaminase (AST) is an enzyme that helps metabolize amino acids, increasing with liver, disease or muscle damage.
• Alkaline phosphatase (ALP), present in liver and bone, aids in protein breakdown. Higher levels may indicate liver damage or bone diseases.
• Albumin is synthesized in the liver and is important for fighting infections and other bodily functions, where lower levels may indicate liver damage or disease.
• Bilirubin, from red blood cell breakdown, passes through the liver and is excreted in stool where, elevated levels may indicate liver damage, disease, or anemia.
• Gamma-glutamyltransferase (GGT) is an enzyme in the blood is an indicator of liver or bile duct damage when elevated.
• L-lactate dehydrogenase (LD) found in the liver, may indicate liver damage when elevated but is also elevated in many other disorders.
• Prothrombin Time (PT) indicates the time it takes for blood to clot, with increased PT indicating liver damage or other blood-thinning factors.

Classification Based on Lab Findings

• Group I: Tests of hepatic excretory function, such as serum bilirubin (total, direct, and indirect).
• Group II: Includes the liver enzymes panel, which marks liver injury/damage (ALT, AST, ALP, GGT).
• Group III: includes plasma protein assessment testing the synthetic function of the liver, like serum albumin, prothrombin time, and total protein.

Classification Based on Clinical Aspects

• Group I: Markers of liver dysfunction, including serum bilirubin, total protein, serum albumin, and prothrombin time.
• Group II: Markers of hepatocellular injury (ALT, AST).
• Group III: Markers of cholestasis (ALP, GGT).

Normal Ranges and Clinical Implications

• ALT: normal range is 7 to 55 U/L, where elevation indicates hepatocellular damage.
• AST: normal range is 8 to 48 U/L, where elevation indicates hepatocellular damage.
• ALP: normal range is 40 to 129 U/L, where elevation indicates cholestasis, impaired conjugation, or biliary obstruction.
• Albumin: normal range is 3.5 to 5.0 g/dL, assessing synthetic function.
• Total protein: normal range is 6.3 to 7.9 g/dL, assessing synthetic function.
• Bilirubin: normal range is 0.1 to 1.2 mg/dL, where elevation indicates cholestasis, impaired conjugation, or biliary obstruction.
• GGT: normal range is 8 to 61 U/L, where elevation indicates cholestasis or biliary obstruction.
• LD: normal range is 122 to 222 U/L, where elevation indicates hepatocellular damage.
• PT: normal range is 9.4 to 12.5 seconds, assessing synthetic function.

Bilirubin Metabolism

• Bilirubin is produced from heme breakdown.
• Unconjugated bilirubin is processed in the liver.
• It becomes conjugated bilirubin and is stored in bile.
• It is transported to the intestines and metabolized into stercobilin and urobilinogen.
• Stercobilin is excreted in feces, while urobilinogen is either excreted in urine or undergoes enterohepatic circulation.

Hyperbilirubinemia Causes

• Isolated increase in unconjugated bilirubin can result from hemolytic disease, genetic disorders (Crigler-Najjar, Gilbert's syndrome), or neonatal/physiological jaundice.
• Isolated increase in conjugated bilirubin can result from cholestasis or genetic disorders (Dubin-Johnson, Rotor's syndrome).
• Increase in both conjugated and unconjugated bilirubin can occur in intrahepatic/liver disorders.

Pathology and Jaundice

• Pre-hepatic (hemolytic) jaundice results from increased Hb breakdown where Intrinsic factors include red blood cell abnormalities and Extrinsic factors include incompatible blood transfusion, and hemolytic disease of the newborn.
• Hepatocellular jaundice is due to disease of the liver's parenchymal cells.
• This results in defective conjugation which includes reduction of functioning liver cells in chronic hepatitis, or defects in the conjugation process like with Gilbert's or Crigler-Najjar syndrome.
• Viral hepatitis and toxic jaundice lead to extensive liver cell damage, causing intrahepatic obstruction and conjugated bilirubin absorption.
• Cholestatic jaundice is caused by drugs like chlorpromazine and steroids, leading to intrahepatic obstruction where liver function remains essentially normal.
• Obstructive or post-hepatic jaundice is due to obstruction of bile flow in extrahepatic ducts, such as from gallstones, pancreatic cancer, or enlarged lymph glands.

Bilirubin Concentration Tests (Van Den Bergh Reaction)

• Serum or plasma samples (EDTA or heparin) needs to be protected from light because direct sunlight exposure can decrease bilirubin levels up to 50% within one hour.
• Measured colorimetrically at 600nm, intensity is proportional to bilirubin levels.
• Direct bilirubin is measured in one minute.
• Total bilirubin: Add activator /accelerator and measure at 30 minutes
• Indirect bilirubin: subtract direct-reacting bilirubin from total bilirubin.
• Direct reaction (soluble): Diazotized sulfanilic acid + Conjugated bilirubin -> Azo bilirubin (reddish purple)
• Indirect reaction (insoluble): Diazotized sulfanilic acid + Unconjugated bilirubin -> Azo bilirubin (no colour)
• If methanol is present the total bilirubin will be measured -> Azo bilirubin (reddish purple)

Lab Results - Serum Bilirubin

• Normal levels in serum: Conjugated levels 0.1-0.4mg/dl, Unconjugated levels 0.2-0.7mg/dl, Urobilinogen 0.4mg/day and Absent Bilirubin present in the urine.
• Prehepatic serum levels: Conjugated levels Normal, Unconjugated levels Increased, Urobilinogen Increased and Absent Bilirubin levels in the urine.
• Hepatic serum levels: Conjugated levels Increased, Unconjugated levels Increased, Urobilinogen Normal/Decreased, Present Bilirubin levels in the urine.
• Posthepatic serum levels: Conjugated levels Increased, Unconjugated levels Normal Urobilinogen Absent, Present Bilirubin levels in the urine.

Plasma Proteins

• The liver synthesizes most, but not all plasma proteins.
• Tests for plasma proteins include total serum proteins, serum albumin, and serum albumin/globulin ratio.

Total Serum Proteins

• Total serum proteins are determined by the Biuret method.
• The Biuret method principle is based on Cu2 ions in biuret reagent complexing with peptide bonds in proteins under alkaline conditions, producing a violet color. Absorbance is measured at 540 nm.
• Total protein increases without altering the albumin-globulin ratio in: dehydration, standing. vigorous exercise, and anticoagulant use.

Albumin

• Albumin production is exclusively in the liver; half-life is 18-20 days.
• Due to its slow turnover rate there is a limitation when using Albumin as an indicator for acute or mild hepatic dysfunction.
• In hepatitis, albumin <3g/dl indicates possible chronic liver disease.
• In portal hypertension, albumin leaks, increasing osmotic pressure and causing ascites.
• Non-hepatic causes of hypoalbuminemia include protein-losing enteropathy, nephrotic syndrome, burns, and severe hemorrhage.

Globulins

• Globulins consist of alpha, beta, and gamma globulins.
• Gamma globulin is produced by plasma cells.
• Alpha and beta globulins are synthesized in the liver.
• Gamma globulin levels elevate in cirrhosis.
• Cirrhotic livers show increased gamma globulin.
• A Polyclonal gamma globulin increase by 100% is an indicator of autoimmune hepatitis
• Increased IgM indicates primary biliary cirrhosis.
• Elevated IgA is indicative of alcoholic liver disease.

Liver Enzymes- Transaminases (AST/ALT)

• Liver enzyme elevation signifies liver cell damage.
• AST (SGOT) is found in liver> cardiac muscle > skeletal muscle> kidneys >brain.
• ALT (SGPT) is found primarily in the liver.
• Serum AST & ALT are normally present at low concentrations (0-40 IU/L).
• Levels >1000 IU/L occur in acute viral hepatitis, toxic and drug-induced hepatitis, or ischemic liver injury.
• AST in alcoholic liver disease is rarely >300 IU/L.
• Minor elevations occur in cirrhosis, hepatitis C, and NASH (50-100U/L).
• A normal AST/ALT ratio is 0.7 to 1.4.
• AST/ALT ratio > 2:1 or > 3:1, indicating ALCOHOLIC liver disease.
• ALT is usually normal in ALD but may be low in alcohol-induced pyridoxal phosphate deficiency.
• AST/ALT <1 is seen in NASH and viral hepatitis.
• Isolated ALT rise is seen in chronic Hep C infection and fatty liver.
• Isolated AST elevation is seen in alcohol-related issues, drug-induced liver injury, hemolysis, and myopathic processes.
• Determination of these enzymes helps distinguish hepatocellular from cholestatic jaundice.
• AST and ALT are much greater in hepatocellular jaundice (>500 IU/L) than in cholestatic jaundice (>200 IU/L).
• Persistent elevation of ALT and AST beyond 6 months indicates chronic hepatitis.

Enzymes Reflecting Cholestasis

• Gamma-glutamyl transpeptidase (GGT) is a sensitive index for liver abnormality.
• Enzyme activity parallels transaminases in hepatic damage.
• Normal range 10-15 U/L.
• Serum GGT increases due to Alcoholism and biliary obstruction.

Alkaline Phosphatase (ALP)

• ALP helps diagnose liver and bone disorders.
• Normal range is 30 - 95 IU/L.
• ALP levels are higher in growing children.
• Elevated serum bilirubin and ALP is usually an indicator of biliary obstruction (obstructive/posthepatic jaundice).
• ALP is elevated in cirrhosis and hepatic tumors.

Enzyme Differences in Jaundice

• Prehepatic jaundice- ALT and AST are usually normal. ALP levels are normal.
• Hepatic jaundice- ALT and AST show a marked increase 500-1500IU/L. ALP levels are elevated slightly at < 30KA/dl.
• Obstructive jaundice- ALT and AST levels are elevated at 100-300IU/L. ALP levels are markedly increased to > 30KA/dl.

42-year-old woman with generalized itching and scleral icterus. Results are

• Total bilirubin: 2.7 mg/dL
• Conjugated bilirubin: 2.4 mg/dL
• Alkaline phosphatase: 253 U/L
• Aspartate aminotransferase: 36 U/L
• Alanine aminotransferase: 40 U/L

Possible diagnosis: Intrahepatic or extrahepatic biliary obstruction

• Unconjugated bilirubin presents normally in plasma, is attached non-covalently to albumin, has a high molecular weight, is not filtered through the kidney and is insoluble in plasma causing brain damage. Indirect Van den Bergh reaction

• Conjugated bilirubin presents normally in bile, is conjugated to glucuronic acid, has a small molecular weight, is filtered through the kidney and is soluble in plasma and can not cross the brain barrier. Direct Van den Bergh reaction

• LFTs indicating synthetic function of the liver are serum albumin, prothrombin time and total protein.

22-year-old intravenous drug addict

• Bilirubin = 93 µmol/L (<20)
• ALT= 761 U/L (<42)
• Alkaline phosphatase = 306 U/L (<250)
• Albumin = 44g/L (35-45)
• y-Glutamyl transferase = 324 U/L (<55)
• Urinary bilirubin positive

Most probable diagnosis:

• Hepatocellular Jaundice
• The bilirubin that is excreted in urine is the conjugated bilirubin
• LFTs that are markers of hepatocellular injury are ALT, AST.

Causes of decrease of plasma albumin concentration due to

• Excessive losses in i.e. urine as in nephrotic syndrome, into the intestine as in protein-losing enteropathy.
• Causes also include: Burns, Severe hemorrhage, Reduced synthesis of albumin as in liver disease, Malnutrition and malabsorption, Increased catabolism of proteins as in fevers.

65-year-old with jaundice, weight loss and pale stools.

• Bilirubin = 250 µmol/L
• ALT = 78 U/L
• AST = 92 U/L
• Alkaline phosphatase = 850 U/L

Most probable diagnosis: Post Hepatic/Obstructive Jaundice

• LFTs that indicate presence of cholestasis, is a blockage in bile flow which are markers of cholestasis are ALP, GGT

49-year-old woman attended her GP with an 8-day history of anorexia, nausea and flu-like symptoms.

• Her urine had been dark in color over the past 2 days. Physical examination revealed tenderness in the right upper quadrant of the abdomen. LFTs were as follows:
• (Bilirubin, 63 µmol/L), (ALT, 936 U/L), (AST, 2700 U/L), (Albumin, 42 g/L), (y-Glutamyl transferase, 312 U/L), (Total protein, 68 g/L), (Alkaline phosphatase, 410 U/L).

The most probable diagnosis is acute hepatocellular damage.

• Major functions of the liver include: Carbohydrate metabolism, Fat metabolism, Protein metabolism, Hormones metabolism, Drugs and Foreign compounds, Storage
• Normal levels of total, direct and indirect bilirubin- Total 1 mg/dl, direct 0.1-0.4 mg/dl and indirect bilirubin 0.2-0.7 mg/dl