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Liver Function Tests (LFTs)Prepared by

Hamad ALAssafalassaf_h@yaho

o.com

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LFTs are blood tests used to diagnose & monitor disease or damage of the liver: 1- Serum Albumin2- Blood Liver Enzymes: - Alanine amino transferase (ALT) - Aspartate amino transferase (AST) - Gamma glutamyl transferase (GGT) - Alkaline phosphatase (ALP)3- Blood Billirubin (total, direct & indirect)4- Blood Coagulation Factors (prothrombin): Prothrombin Time (PT) 5- Markers of liver fibrosis

Routine Liver Function Tests (LFTs)

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• Albumin is present in higher concentrations than other plasma proteins ( ~ 40 g/L in normal adults).

• Albumin is synthesized in the liver & has a half-life of 20 days.• Very small amounts of albumin cross the

glomerular capillary wall. Accordingly, no more than traces of

albumin may normally appear in urine that can not be detected by ordinary laboratory means. • Albuminuria : In this case, albumin can

be detected in urine by ordinary laboratory means due to physiological or pathological conditions.

Serum Albumin

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Causes of hypoalbuminemia:

Artifactual: Diluted samplePhysiological : Pregnancy Decreased amino acids: Reduced

essential amino acids in diet & reduced synthesis of nonessential amino acids due to either Malnutrition or Malabsorption.

Increased catabolism : Surgery, Trauma, Infections.

Defective synthesis in liver: Chronic liver diseases (liver cirrhosis)

Increased loss : From the kidney (Nephrotic syndrome) or From GIT (Protein loosing entropathies)

Serum Albumin

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• Aminotransferases (ALT & AST) are normally intracellular enzymes.

• Elevated blood levels of aminotransferases indicate damage to cells rich in these enzymes (as disease to tissue or physical trauma )

• Blood AST & ALT are of particular diagnostic value

Blood Aminotransferases

(ALT & AST)

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1- Viral , toxic or alcholic hepatitis: Highly increase in ALT & AST (Up to 20 -

50 folds). In viral hepatitis, ALT is much elevated than

AST2- Cirrhosis (chronic liver diseases): Moderate increase (up to 4 – 5 folds) In chronic cases, AST is much elevated than

ALT.3- Obstructive jaundice: Moderate increase ALT & AST are increased

up to 3 folds.

4- After alcoholic or drug intake: Transient slight to moderate increase.

Causes of elevated levels of blood ALT & AST

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ALT is more liver specific than AST. ALT rarely increases in lesions other than the

liver parenchymal ALT elevations persist longer than do AST. Formerly named as Glutamate pyruvate

transferase (GPT) 

Blood levels of AST are increased with many diseases of various organs:

1- Liver diseases 2- Myocardial infarction (MI) 3- Progressive skeletal muscular dystrophy4- Crush injury 5- Hemolytic diseases6- Artifact: in hemolysed samples or if serum separation is delayed. Formerly named as Glutamate oxaloacetate

transferase (GOT)

Alanine amino transferase (ALT)

Aspartate transaminase (AST)

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GGT present in blood originates primarily from hepatobiliary system

Causes of increased blood GGT:1- Induction of GGT synthesis by these cells occurs without cell damage by alcohol or drugs as anticonvulsants.2- Biliary obstruction: GGT is markedly increased with obstructive

jaundice (5 – 30 folds) Increase earlier (more sensitive) than ALP Persists longer than ALP3- Viral, toxic & alcoholic hepatitis : Increase is only 2 – 5 folds (less sensitive than ALT & AST) 4- Primary and secondary liver tumors: GGT is elevated earlier than other enzymes in liver

neoplasm. Secondary of other organ tumors in the liver can be

early detected by elevated GGT. (arouse suspicious that the diseases is metastatic to liver)

Gamma glutamyl transferase (GGT)

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Main Sources of ALP:1- Cells of hepatobiliary tract (hepatocytes adjacent to the biliary canalculi).2- Osteoblasts of bone : 3- Other Sources: Intestine and placenta & renal tubules.

If ALP is elevated due to a bone disease

In this case, GGT is normal i.e. GGT is used to ascertain whether

increased ALP is due to bone or hepatobiliary disease

Alkaline Phosphatase (ALP)

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Clinical significance of increased serum ALP activities:

1- Physiological increase of ALP: During periods of active bone growth in infancy

and at puberty. Preterm infants total ALP is increased to 5 times

the upper reference limit of adults due to bone isoenzymes.

In children under 3 years, total ALP activity is increased up to 2.5 times the upper limit.

Increased twice, during the second and third trimesters of pregnancy (placental ALP).

Alkaline Phosphatase (ALP) cont.

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2- Pathological increase of ALP:A- Bone causes: (due to increased osteoblastic activity):

Tumors (osteogenic) Paget`s Disease of bone: Marked

increase (10 – 25 folds) Primary osteogenic tumors Secondary malignant deposits in bone

if causing osteoblastosis Rickets & osteomalacia (vitamin D

deficiency) Primary & secondary

hyperparathyroidism (increased PTH) Healing of bone fractures

Alkaline Phosphatase (ALP) cont.

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B- Hepatobiliray tract: liver diseases with involvement of biliary tract.1- Obstructive jaundice: Extrahepatic cholestiasis : (Marked

increase, up to 10 – 12 folds)Due to obstruction of to the flow of bile through the biliary tract e.g. Gallstones, cholecystitis. Intrahepatic cholestiasis: (Moderate

increase , ~ 3 -5 folds)Bile secretion from the hepatocytes into the canalculi is impaired e.g. cholangitis.

2- Viral, toxic & alcoholic hepatitis: Mild to moderate increase, less than 3 folds.

Alkaline Phosphatase (ALP) cont.

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• The liver makes many of the proteins (clotting factors) needed to make blood clot.

• In certain liver disorders the liver cannot make enough of these proteins and so blood does not clot so well.

Therefore, blood clotting tests may be used as a marker of the severity of certain liver disorders

• In liver disease, the synthesis of prothrombin & other clotting factors is diminished prolonged prothrombin Time (PT)

• This may be one of the earliest abnormalities seen in hepatocellular damage, since prothrombin has a short half-life (~ 6 hours)

Coagulation factors

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• Procollagen type III terminal peptide

• Hyaluronic acid (hyaluronin)

Markers of Liver Fibrosis

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-Fetoprotein

• One of the major plasma proteins in fetal life.• Falls thru-out gestation and by age one year• In acute hepatic injury AFP 10 – 20 folds.• Used to screen and diagnose Hepatocellular

carcinoma & hepatoblastoma.

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Ammonia Ammonia is produced by all

tissues from the catabolism of amino acids

Ammonia is mainly disposed is via formation of urea in liver

Blood level of ammoina must be kept very low, otherwise, hyperammonemia & CNS toxicity will occur

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Ammonia

catabolism of amino

acidsWith production

of

In Liver

UreaSmall

amount excreted in urine

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Hyperammonemia Increase of ammonia level of blood

Normal level of blood ammonia is 5-50 mmol/L

Hyperammonemia : A medical emergency as ammonia has a direct neurotoxic effect on CNS

Ammonia intoxication: It is defined as toxicity of the brain due to increase in ammonia level in the systemic blood.

At high concentrations, ammonia can cause coma & death

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Causes of Hyperammonemia

1- Liver diseases: are common causes in adults

i- Acute causes: viral hepatitis, ischemia, hepatotoxins

ii- Chronic causes: liver cirrhosis due to alcoholism, hepatitis, biliary obstruction.

2 - Gatrointestinal Bleeding: By action of bacteria of GIT on blood urea

with production of much amounts of ammonia that is absorbed to blood.

3- Ornithine transcarbamoylase

deficiency (Hereditary)

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Hyperammonemia in Renal Failure

Renal Failure

blood urea levels are elevated

Transfer of urea to intestine is increased

Much amounts of Ammonia is formed by bacterial urease

Absorbed to blood

Hyperammonemia

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Precautions resampling, handling A free‐flowing venous (or arterial) blood sample

should be collected into a specimen tube (preferably pre‐chilled) containing either lithium heparin or EDTA

As difficult venepuncture can cause a spurious increase in [ammonia].

The sample should be transported on ice to the laboratory, separated within 15 minutes of collection and analyzed immediately.

These precautions are necessary as the [ammonia] of standing blood increases spontaneously, due to generation and release of ammonia from red blood cells

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Bilirubin and Jaundice

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Formation of Bilirubin from Heme

Breakdown of RBCs

Heme

Biliverdin (green)

Bilirubin (red-orange) bile pigments

In Blood with albuminUNCONJUGATED BILIRUBIN (or INDIRECT

BILITUBIN)

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Bilirubin Metabolism in the Liver

• Uptake of Bilirubin by hepatocytes: Bilirubin dissociates from its carrier albumin & enters hepatocytes

• Conjugation of Bilirubin: In hepatocytes, bilirubin is conjugated with two molecules of glucuronic acid by the enzyme glucuronyl transferase

• Excretion of bilirubin into bile: Conjugated bilirubin (Direct bilirubin) is transported into bile canalculi & then into bile.

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Bilirubin Metabolism in the Intestine

Conjugated bilirubin                                                          bacteria                                                              in the intestine  Urobilinogen

Stercobilin Reabsorbed in stool (brown) Kidney Urine Urobilin (yellow)

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Jaundice• Yellow color of skin, nail beds &

sclera caused by deposition of bilirubin secondary to increased bilirubin levels in blood (hyperbilirubinemia)

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Types of Jaundice1- Hemolytic Jaundice: Massive lysis of RBCs in hemolytic anemia e.g. sickle cell anemia & G6PD deficiency anemia & Hemolytic transfusion reaction.2- Obstructive Jaundice: Conjugated bilirubin is prevented from passing to the intestine. As in Gallstones.3- Hepatocellular Jaundice: Liver damage (by hepatitis or cirrhosis) causes low conjugation efficiency leading to increased unconjugated (indirect) bilirubin in blood.

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LABORATORY INVESTIGATIONS IN TYPES OF JAUNDICE

Urine BloodUrobilino

genBilirubin

Indirect

bilirubin

Direct bilirubi

nAST &

ALTALP & GGT

Hemolytic

jaundiceIncrea

sed Nil increased

Normal

Normal

Normal

Obstructive

jaundice

Decreased or

absentPrese

ntNorma

lincreased

Normal or mild increas

ed

Marked

increased

Hepatocellular

jaundice

Decreased or

absentPrese

ntIncreased

increased

Marked

increased

Normal or mild increas

edNormal Range

Indirect Bilirubin

< 5.13 µmol/L

Direct Bilirubin

< 13.7 µmol/L

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Jaundice in Newborns

In newborns (especially premature) Bilirubin accumulates as the liver enzyme bilirubin glucuronyl transferase (responsible for conjugation of bilirubin) is low at birth. (The enzymes reaches adult levels in about 4 weeks).• Accordingly, unconjugated bilirubin is increased in blood. • Elevated bilirubin in excess of the binding capacity of albumin

can diffuse into basal ganglia & cause toxic encephalopathy (kernicterus)

Treatment • Exposure of the newborn skin to blue fluorescent light which

converts bilirubin to more polar & hence water-soluble isomers • These isomers can be excreted into bile without conjugation to

glucuronic acid.

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Congenital hyperbilirubinemiaBilirubin is elevated in blood due to inherited defects in

the bilirubin metabolic pathway

1- Crigler-Najjar syndrome Low activity of glucoronyltransferase (conjugating enzyme) Severe hyperbilirubinemia in neonates (unconjugated bilirubin),

Complicated by kernicterus & early death

2- Gilbert`s syndrome Decreased production of glucoronyltransferase More common in men, Occurs in 2-3 % of men. Usually asymptomatic hyperbilirubinemia with Normal Liver

function tests.3- Dubin-Johnson syndrome Defect in transfer of conjugated bilirubin into the biliary canalculi

Conjugated hyperbilirubinemia.