Evaluation of Biochemical Tests in Liver Disorders

By: Capt Arabinda Mohan Bhattarai

Guide: Col HS Batra

AIM• To discuss the normal physiological function of liver.

• To evaluate abnormal liver function tests findings in liver disorders.

• Approach to various liver disorders.

Introduction

• The liver has a central and critical biochemical role in

metabolism

digestion

detoxification and

elimination of substance from the body

DEGRADATION OF HEME TO BILIRUBIN

85% is derived from RBCs

· In normal adults this results in a daily load of 250-300 mg of bilirubin

· Normal plasma conc is less than 1 mg/dL

· Hydrophobic – transported by albumin to the liver for further metabolism prior to its excretion

“unconjugated” bilirubin

Bilirubin Metabolism

Excretory function

• Bilirubin: Orange-yellow pigment derived from heme, as a product of red blood

cell turnover.

250-350 mg of bilirubin produced daily, 85% from RBCs.

Transported across the hepatocyte membrane, conjugated with glucuronic acid and excreted into bile by an energy dependent process.

Serum Bilirubin – Estimation• Principle: When diazotised sulfanilic acid reacts with bilirubin, it

forms ‘azobilirubin’, a purple coloured product measured colorimetrically. This reaction is known as Van den Bergh reaction.

Conjugated bilirubin gives colour immediately (<1min) ‘Direct positive’.

Unconjugated bilirubin gives colour only after addition of methanol ‘Indirect positive’(within 30 mins)

Both conjugated and unconjugated ‘Biphasic’(immediately direct positive intensified by addition of alcohol indirect positive)

Fouchet’s Test

• Bilirubin in urine implies increased serum direct bilirubin and excludes hemolysis as the cause

• Bile pigments adhere to the precipitate of barium sulphate.

• On addition of Fouchet’s reagent, ferric chloride in the presence of trichloroacetic acid oxidises yellow colour bilirubin to green colour biliverdin and blue coloured cyanobilirubin forming pista green colour.

Bile Salts

• Source: cholesterol

• Primary bile acids: cholic and chenodeoxycholic acid.

• Metabolised by intestinal bacteria to secondary bile acids: deoxycholic and lithocholic acid.

• Bile salts are Glycocholates and Taurocholates.

• Emulsification of Fatty acids

Detoxification function

• Conversion of ammonia to Urea.

• Drug metabolism (Xenobiotics).

• Hippuric acid synthesis test

Synthetic Function

• Synthesis of Plasma proteins like Albumin, Transthyretin, Prothrombin and Fibrinogen.

• Clotting factors except Von Willebrand factor and inhibitors of coagulation, such as antithrombin.

• Post-translational carboxylation of (II, VII, IX and X) require vitamin K, occurs within the hepatocyte

Synthetic Function

• Albumin:

Synthesized exclusively by liver.

Synthesis is inhibited by interleukin (IL)-6 in inflammatory conditions.

Decreased concentrations in cirrhosis, autoimmune hepatitis and alcoholic hepatitis.

Dye binding method (BCG) for estimation of albumin may give false low values in patients with jaundice due to interference with bilirubin.

Synthetic Function

• Determination of total plasma proteins and A:G ratio.

• Severe or fulminant hepatic failure: concentration of short lived hepatic proteins (transthyretin and

prothrombin) fall quickly. minimal change in proteins with longer half lives.

• Decrease in fibrinogen levels <100 mg% seen in parenchymal liver disease, acute hepatic necrosis.

Prothrombin Time

• It measures the activity of fibrinogen (I), Prothrombin (II) and factors V, VII and X

• Prolonged PT indicates liver disease

• PT measures the time to clot after exposure of plasma to tissue factor.

• INR=[PT (patient)/PT (geometric mean of normal)]ISI

Prothrombin Time

• Prolonged due to lack of synthesis in hepatocellular disease or due to lack of Vitamin-K absorption in obstruction

• Markedly prolonged PT indicates severe liver damage in hepatitis and cirrhosis.

• Corrected within 24-48 hours by parenteral administration of vitamin K (10mg/day for 3 days) in obstructive but not in hepatocellular jaundice.

Carbohydrate metabolism

• Blood glucose levels maintained During short fasts by hepatic glycogenolysis. Prolonged fasts by hepatic gluconeogenesis

• Tests based on carbohydrate metabolism: Galactose tolerance test

• Hypoglycemia is a common complication in liver diseases like Reye’s syndrome, fulminant hepatic failure and advanced cirrhosis

Lipid Metabolism

• Metabolism of cholesterol, synthesis, esterification, oxidation and excretion.

• Cholesterol-Cholesteryl ester ratio:

• Normal level- 150 mg to 250 mg, 60-70% as ester.

• Cholesterol endogenously synthesized in liver.

• Acute hepatic necrosis marked reduction in esters.

• Cirrhosis- decrease in HDL.

• Alcohol induced liver injury increase in HDL levels.

Serum Enzymes

• Plasma activities of several cytosolic, mitochondrial, and membrane associated enzymes are measured.

• Ability of liver enzymes to assist in diagnosis depends on

tissue specificity subcellular distribution relative activity of enzyme in liver and plasma patterns of release clearance from plasma.

AST( SGOT)• Present in cytoplasm as well as mitochondria of hepatocytes.

• Mitochondrial isoenzyme represents a significant fraction of total AST within hepatocytes, half lives of 87 hours.

• Require pyridoxal phosphate as cofactor.

• Plasma half lives of AST is 17 hours

• Upper reference range limits of 40 IU/L.

• Total cytoplasmic AST is present in highest activity in hepatocytes 7000 times higher than plasma

ALT (SGPT)

• Plasma half life is 47 hours

• Liver specific activity in hepatocytes 3000 times higher than plasma which is almost half of AST.

• Mitochondrial isoenzyme has very low half life making it insignificant in diagnosis

Patterns of release

• In most forms of acute hepatocellular injury AST is higher than ALT initially, due to higher activity of AST in hepatocytes

• Within 24-48 hours, if ongoing damage occurs ALT will become higher than AST due to its longer half life.

Patterns of release

• In Alcoholic liver disease studies suggest that alcohol induces mitochondrial damage.

• This causes release of mitochondrial AST which besides predominant AST in hepatocytes has significant longer half life than extramitochondrial AST and ALT causing AST:ALT ratio (De Ritis Ratio of 3-4:1)

Activity

• AST/ALT ratio >2 with ALT <300 U/L suggestive of alcoholic hepatitis.

• ALT more specific for liver disease.

• Greater increase in AST than ALT favor viral hepatitis, post hepatic jaundice.

Alkaline Phosphatase• Present in number of liver tissues including liver, bone, kidney and

intestine.

• Liver isoenzyme has half life of 3 days

• Normal range: 20-130 IU/L.

• Increased in cholestasis, obstructive jaundice.

• ALP and GGT are membrane bound glycoprotein enzymes found at the canalicular membrane of hepatocytes

ϒ-Glutamyl Transferase

• Regulates the transfer of amino acids across cell membranes.

• If ALP and GGT are both elevated source is likely to be hepatic.

• Levels increased in about 60-70% chronic alcoholics.

• Normal Range: 5-40 IU/L

Mechanism of release

• Bile acids, solubilize the release of GGT and ALP from plasma membrane.

• Ethanol, Phenytoin and Carbamazepine induce microsomal enzyme synthesis lead to increase in GGT and ALP

5’- Nucleotidase

• Increased in cholestatic disorders.

• No increase in activity in patients with bone disease

• Confirms the increase in ALP from hepatic source.

Lactate Dehydrogenase

• Cytosolic glycolytic enzyme catalyses the reversible oxidation of lactate to pyruvate.

• Normal upper limit: 150 U/L

• Liver isoenzymes have half life of 4-6 hours and low activity (about 500) times than plasma.

• Space occupying lesions of liver, metastatic carcinoma lead to increase in LDH> 500 IU/L and ALP> 250 IU/L.

Rate of clearance

• The half life of ALT is 47 hrs, cytoplasmic AST is 17 hrs.

• Liver isoenzyme of ALP is 3 days.

• GGT –10 days

• The removal of enzymes takes place by receptor- mediated endocytosis by liver macrophages.

• Conjugated bilirubin binds covalently to albumin and is stays longer in the blood.

Biliprotein/ Delta Bilirubin

• Formed by covalent attachment of Bilirubin monoglucuronide with lysine residues of albumin or other proteins postsynthetically.

• Increased levels are markers of hepatic dysfunction.

Cirrhosis• Earliest laboratory abnormalities are: fall in platelet count increase in PT decrease in albumin to globulin ratio <1 increase in AST/ALT > 1

• End stage cirrhosis- massive tissue destruction, decrease in AST and ALT.

Model for End Stage Liver Disease(MELD)

• MELD is calculated as

= 3.8[Ln Serum bilirubin (mg/dL)]+11.2 [Ln INR]+9.6 [Ln Serum Creatinine

(mg/dL)]+ 6.4

• Identify patients with advanced cirrhosis, candidates for liver transplantation.

• Superior to Child-Pugh scoring in predicting short term survival

• Risk of death over 3 months is Low if score <10, intermediate if 10-20 and high if >20

Viral Hepatitis• Acute viral hepatitis is defined by the sudden onset of significant

aminotransferase elevation as a consequence of diffuse necroinflammatory liver injury.

• This condition may resolve or progress to fulminant failure or chronic hepatitis

• Chronic viral hepatitis is defined as the presence of persistent (at least 6 months) necroinflammatory injury that can lead to cirrhosis.

• Histopathologic classification of chronic viral hepatitis is based on etiology, grade, and stage.

Features of viral hepatitisFeature HAV HBV HCV HDV HEV

Incubation (days) 15–45, mean 30 30–180, mean 60–90

15–160, mean 50 30–180, mean 60–90

14–60, mean 40

Onset Acute Insidious or acute Insidious Insidious or acute Acute

Clinical Severity

Mild Occasionally severe

Moderate Occasionally severe

Mild

Fulminant 0.1% 0.1–1% 0.1% 5–20% 1–2%

Progression to chronicity

None Occasional (1–10%) (90% of neonates)

Common (85%) Common None

Carrier None 0.1–30%

1.5–3.2% Variable None

Cancer None + + ± None

Prognosis Excellent Worse with age, debility

Moderate Acute, goodChronic, poor

Good

Algorithm for workup for Jaundice

Crigler-Najjar Syndrome

• Hereditary Glucuronyl Transferase Deficiency.

• Familial autosomal recessive disease (type I) and autosomal dominant (type II)

• Indirect serum bilirubin is increased, appears first or second day of life and persists for life.

• Type I complete enzyme deficiency, type II partial deficiency

Gilbert’s Syndrome

• Autosomal dominant

• Chronic, benign, intermittent, nonhemolytic and unconjugated hyperbilirubinemia.

• Defective transport and conjugation of unconjugated bilirubin.

• Jaundice is accentuated by pregnancy, fever, exercise and various drugs including alcohol.

Dubin-Johnson Syndrome• Autosomal recessive disease.

• Conjugation of bilirubin-diglucuronide is normal

• Inability to transport bilirubin-glucuronide through hepatocytes into canaliculi

• Symptoms: mild chronic recurrent jaundice and hepatomegaly

• Serum bilirubin (3-10 mg/dL rarely ≤ 30 md/dL), significant is direct.

Rotor’s Syndrome• Autosomal recessive

• Asymptomatic, benign defective uptake and storage of conjugated bilirubin, possibly in transfer of bilirubin from liver to bile.

• detected in adolescents or adults

• Jaundice accentuated by pregnancy, pills and alcohol

• Conjugated hyperbilirubinemia (<10 mg/dL)

Take Home Message

• Liver has central role in

metabolism, synthesis

and detoxification in

the body

• Interpretation of

liver function tests help in

early diagnosis of various

disorders.

References

• Tietze Textbook of clinical chemistry and molecular diagnostics-5 th Ed.

• Intepretation of Diagnostic Tests, Jacques Wallace-7th Ed.

• Textbook of Biochemistry with clinical correlations, Devlin-6th Ed

• Clinical Diagnosis and management by Lab methods- Henry 18th Ed

THANK YOU

Questions?