Download Liver Function Tests slides 2009

Liver Function
Tests
First Lecture
Contents:
• Introduction to normal liver functions
• Structural Unit
• Physiology
• Liver Function Tests
• Bilirubin Metabolism
• Jaundice
Introduction:

The liver is the largest organ in the body.

It consists of two main lobes that together
weigh from 1400 to 1600 g in the normal
adult .

It is reddish brown in color and has a rich
blood supply 1500 ml/min from two major
vessels, the hepatic artery and the portal vein
The hepatic artery, a branch of the aorta,
contributes 20 % of the blood supply and
provides most of the oxygen requirement.

The portal vein , which drains the GIT ,
transports the most recently absorbed
materials from the intestines to the liver.

Structural Unit:
 The lobule which measures 1-2 mm in
diameter, forms the structural unit of the
liver.
 It is composed of cords of liver cells
(hepatocytes) radiating from a central vein.
 The boundary of each lobule is formed by a
portal tract made up of connective tissue
containing a branch of the hepatic artery,
portal vein and bile duct.

Between the cords of the liver cells are vascular spaces,
called sinusoids, that are lined by endothelial cells and
Kupffer’s cells

The Kupffer’s cells are phagocytic macrophages capable
of ingesting bacteria or other foreign material from the
blood that flows through the sinusoids

Primary bile canaliculi are located between the
hepatocytes

Hepatocytes form 60% , Kupffer’s cells 30%, endothelial
cells, connective tissue and bile ducts 10% of the liver
Physiology:

The liver has a central role in the
metabolism of carbohydrates, lipids,
proteins, vitamins and hormones, as well
as a role as a storage and excretory
organ.

It has an important role in detoxification
and drug metabolism.
Major Synthetic Activity of the liver:
• Synthesis of proteins, carbohydrates, and lipids.
• The liver plays an important role in synthesizing
albumin and the majority of the - and - globulins.
• All the blood-clotting factors (except VIII) are also
synthesized in the liver.
• Deamination of glutamate in the liver is the primary
source of ammonia, which is then converted to urea.
• The synthesis and metabolism of carbohydrates is also
centered in the liver (Glucose is converted to glycogen, a
portion of which is stored in the liver and later
reconverted to glucose as necessary).
• An additional important liver function is
gluconeogenesis from amino acids.
• Fat is formed from carbohydrates in the liver when
nutrition is adequate and the demand for glucose is being
met from dietary sources.
• The liver also plays a key role in the metabolism of fat.
• It is the major site for :
• the removal of chylomicron remnants
• the conversion of acetyl CoA to fatty acids,
triglycerides, and cholesterol.
• Metabolism of cholesterol into bile acids
• Very low-density lipoproteins (VLDL), which
are responsible for transporting triglycerides
into the tissues, are synthesized primarily in the
liver.
• High-density lipoproteins (HDL) are also made
in the liver.
• Formation of ketone bodies occurs almost
exclusively in the liver (When the demand for
gluconeogenesis depletes oxaloacetate and acetyl CoA
cannot be converted rapidly enough to citrate, acetyl
CoA accumulates, and a decyclase in the liver
liberates ketone bodies into the blood).
• The liver is the storage site for all the fat-soluble
vitamins (A, D, E, and K) and several water-soluble
vitamins, such as B12.
• Another vitamin-related function is the conversion of
carotene into vitamin A.
• The liver is the source of somatomedin (an insulin-like
factor that mediates the activity of growth hormone) and
angiotensinogen, and is a major site of metabolic
clearance of many other hormones.
MITOCHONDRION
Fatty acids
-oxidation
OAAmalatepyruvate+NADPH
malic enzyme
oxaloacetate
Citrate
Citrate
Lyase (requires ATP)
(2) Acetyl CoA
CoA
(2) Acetyl CoA
Thiolase
Thiolase
Acetoacetyl CoA
AcetylCoA
HMG CoA synthase
CoA
AcetylCoA
Acetoacetate
HMG CoA lyase
-HBDH
NADH
Acetoacetyl CoA
HMG-CoA
synthase
HMG CoA
HMG CoA
-hydroxybutyrate
cytoplasm
HMG CoA
reductase
smooth
endoplasmic
reticulum
Mevalonate
NAD+
Ketone bodies (only synthesized in liver)
CHOLESTEROL
Figure 5. Ketone body formation (ketogenesis) in liver and its relationship to
cholesterol synthesis
Liver function tests

The routine liver function tests include the
measurement of :
- Total , direct and indirect bilirubin
- Total proteins and albumin
- Liver enzymes include :

ALT ( Alanine transaminase )

AST ( Aspartate transaminase )

ALP ( Alkaline phosphatase )

GGT (  - Glutamyl transferase )
• The routine liver function tests include the measurement of
Total and Direct Bilirubin, Total proteins and Albumin and
Liver enzymes including ALT, AST, ALP and GGT.
• Not all of these tests are related to the function of the liver.
Standard group of tests Property being assessed
Plasma albumin
Plasma bilirubin (total)
Protein synthesis
Hepatic anion transport
Plasma enzymes activities:
- ALT, AST
Hepatocellular integrity
- ALP, GGT
Presence of cholestasis
 Not all of these tests are related to the functions of the
liver.
 Except for the screening of healthy people (for
insurance examinations or occupational medicine),
liver function tests are usually employed in patients to:
 Confirm a clinical suspicion of the presence of liver
disease.
 Give an idea about the severity and prognosis of the
liver disease.
 Follow up the disease and evaluate therapy.
 Arrive at a differential diagnosis (e.g. cholestatic vs
hepatocellular liver disease).
Bilirubin Metabolism
1. Reticulo-endothelial System:

It is mainly in liver, spleen and bone marrow.

80% of bilirubin formed from heme each day
arise from red blood cells.

The remaining 20% comes from red cell precursors
destroyed in the bone marrow (ineffective
erythropoiesis), and from other heme proteins
such as myoglobin, cytochromes, catalase and
peroxidase.

Iron is removed from the heme molecule and the
porphyrin ring is opened to form bilirubin.
Bilirubin:
 is a yellow pigment, its normal plasma level is 2-17 mol/L.
 is soluble in lipid solvents but almost insoluble in water.
 These characteristics enable it to cross cell membrane readily, but
special mechanisms are needed to make it water-soluble for
carriage in plasma by protein-binding mainly to albumin 
forming indirect or unconjugated bilirubin.
 In this form, it does not readily enter most tissues, nor it is filtered
at the glomerulus.
 The maximum capacity of albumin for bilirubin is 340 mol/L.
Above this, it will lead to kernicterus in the newborn babies.
2. Liver:
a) Hepatic uptake:
The bilirubin-albumin complex appears to be
associated by receptors on the plasma
membrane of the hepatocytes, bilirubin taken
up by a specific carrier (facilitated diffusion),
leaving albumin in the plasma.
b) Conjugation:
Conjugation of bilirubin within the hepatocytes
makes it water-soluble. The enzyme is BilirubinUDP-glucuronyl transferase forms bilirubin –
diglucuronide (direct or conjugated bilirubin).
c) Secretion of bilirubin into bile:
Occurs against a high concentration gradient,
a carrier mediated energy dependant process
(active secretion).
3. Intestine:
 Bilirubin diglucuronide is degraded by bacterial
action, mainly in the colon, being deconjugated
and then converted into a mixture of compounds
collectively termed urobilinogen
(stercobilinogen).
 Urobilinogen is water-soluble, mostly excreted
in the feces but a small percentage (20%) is
reabsorbed and then mostly re-excreted by the
liver.
 After excretion, urobilinogen (colorless) is
oxidized to urobilin (stercobilin) which is
brown gives stools its color.
 Some of the reabsorbed urobilinogen passes
through the liver into the systemic circulation
and is then excreted in the urine (urobilin)
gives the urine its yellow color .
Jaundice

Jaundice is the yellowish discoloration of the
skin and sclera due to hyperbilirubinemia.

Normally, more than 95% of bilirubin in the
plasma is indirect (unconjugated).

Jaundice becomes clinically apparent when the
plasma bilirubin exceeds 50 mol/L.
Jaundice may be classified into:
1) Pre-hepatic Jaundice:
 The production rate of bilirubin is increased, exceeding the
excretory capacity of the liver.
 Overproduction of bilirubin occurs in all forms of
hemolytic anemia, less commonly, in conditions where
there is much ineffective erythropoiesis (e.g. pernicious
anemia).
 Hematomas can also cause pre- hepatic jaundice. There is
increase in plasma indirect (unconjugated) bilirubin .
 Bilirubin is not excreted in urine.
 Urinary urobilinogen concentration is increased.
2) Hepatocellular Jaundice:
 Hepatocellular damage due to viral hepatitis
or toxins may interfere with the uptake of
bilirubin, or with its conjugation or with
secretion of conjugated bilirubin into bile.
 Both indirect and direct hyperbilirubinemia
may occur in hepatocellular jaundice.
 Bilirubin and excess urobilinogen are found in
urine.
3) Obstructive (Cholestatic) Jaundice:

It is due to impaction of gallstones in the
common bile duct or carcinoma of the head of
pancreas or of the biliary tree.

Jaundice is due to conjugated (direct) bilirubin.

Bilirubin is detected in urine.
Congenital Hyperbilirubinemias:
They are all due to inherited defects in the
mechanism of bilirubin transport.
1) Gilbert’s Disease :
 A common congenital disorder (autosomal
dominant) of bilirubin transport affecting
approximately 2% of the population, males more
affected than females.
 The pathogenesis of the disease is complex. The
activity of UDP-glucuronyl transferase is reduced
and defects in the uptake of bilirubin by
hepatocytes also occur.
 Gilbert’s disease characteristically  mild
fluctuating jaundice .
 Most patients have a plasma bilirubin less than
50 mol/L.
 Hemolysis is absent , other liver function tests are
normal and there are no histological changes in the
liver.
 Gilbert’s disease is a benign condition and life
expectancy is normal.
 It often presents in young adults and must be
differentiated from other causes of unconjugated
hyperbilirubinemia, such as hemolysis or hepatitis.
 In Gilbert’s disease, bilirubin concentrations:
  with a 400 Kcal/day for 72 hours diet.
  following phenobarbitone administration.
2) Crigler-Najjar Syndrome
• This rare condition is due to low activity of
bilirubin UDP-glucuronyl transferase.
• Gives rise to severe hyperbilirubinemia in
neonates  kernicterus & often early death.
3) Dubin –Johnson Syndrome & Rotor’s
Syndrome:
 These
rare disorders are characterized by a benign
conjugated hyperbilirubinemia, accompanied by
bilirubinuria.

In both syndromes, there is a defect in the transfer of
conjugated bilirubin into the biliary canaliculi.

Urinary coproporphyrins are :
- Normal in Dubin-Johnson syndrome
-  in Rotor’s syndrome.

A blackish-brown pigment is found in the liver in
Dubin-Johnson but not in Rotor’s syndrome.
Second Lecture
Contents:
• Hepatic protein synthesis
• Albumin
• Blood Coagulation Factors
• Immunoglobulins
• Hepatic Enzymes
• ALT, AST, ALP, & GGT
• Biomarkers for hepatic fibrosis
• Other Liver Function Tests
• Tests for functional liver mass
• Bile acids
Hepatic Protein Synthesis
I. Albumin:
Albumin has a long half-life of 20 days and
levels fall slowly if no synthesis occur. Thus,
serum albumin is usually normal in acute
hepatitis. However, in chronic liver diseases
such as cirrhosis, impaired synthesis may lead to
low serum levels.


Serum albumin levels may be low due to:
-  protein intake or
-  degradation and loss into urine, gut or into a
third compartment (ascitis).

Serum globulins are usually  in cirrhosis.
II- Coagulation factors:
• In liver disease the synthesis of prothrombin and
other clotting factors is diminished,  prolonged
Bleeding Time (BT).
• This may be one of the earliest abnormalities
seen in hepatocellular damage, since
prothrombin has a short half-life (~ 6h).
• Deficiency of fat soluble vitamin K due to
failure of absorption of lipids  prolonged
BT.
• In vit. K deficiency the coagulation defect
can often be corrected by parentral
administration of vit. K.
III- Immunoglobulins:
• Plasma Ig measurements are of little value in
liver disease, because the changes are of low
specificity.
• In most types of cirrhosis  plasma IgA.
• In primary biliary cirrhosis  plasma IgM.
• In chronic active hepatitis   plasma IgG.
Hepatic Enzymes
a) Aminotransferases (ALT & AST):

Aminotransferases are involved in amino acid
metabolism.

AST occurs in both the cytosol and
mitochondria of cells while ALT is a cytosolic
enzyme.

 amounts of both transaminases leak from
inflamed or damaged hepatocytes due to acute
or chronic hepatitis.

ALT is more specific for liver disease than AST .
b) Alkaline Phosphatase (ALP):
• Originates from the liver, bone
(reflecting osteoblastic activity) and the
placenta.
• Levels of ALP  in cholestasis, mainly
because of increased synthesis.
c)  - Glutamyl transferase (GGT):

 serum levels of GGT are found in
both hepatocellular and cholestatic disease.


Higher levels are found in cholestasis.
 synthesis of GGT is induced by excessive
ethanol intake.
N.B. Hepatic Enzymes:



ALT and AST levels are  mainly in
hepatocellular disease.
ALP level is raised mainly in obstructive
liver diseases.
Serum GGT levels are modest  in
hepatocellular disease and marked  in
obstructive disease.
Makers of fibrosis
• A Varity of markers have been described that
may be of help in measurement of hepatic
fibrosis.
• Procollagen type III terminal peptide and
hyaluronic acid (hyaluronin) are the most
commonly used tests.
Other Liver Function Tests
A. A number of liver function tests have been
described to give an indication of the
functional liver mass.
•
These tests are not often used but include :
–
–
the aminopyrine breath tests.
the galactose elimination test.
B. Bile Acids :
•
The measurement of bile acids is useful in:
–
Investigation of hepatic dysfunction associated
with pregnancy .
–
investigation of Gilbert’s syndrome.
The End