Liver enzymeALTASTALPGGT Liver is the largest Organ of the body weighing about 15 Kg Liver is called kitchen of our body Major Metabolic Functions of the Liver Synthetic Function Plasma proteins albumin globulins cholesterol triglycerides and lipoproteins ID: 908443
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Slide1
Liver function test
Part 1
Liver enzyme(ALT-AST-ALP-GGT)
Slide2Slide3Liver is the largest Organ of the body weighing about 1.5 Kg.
Liver is called kitchen of our body.
Slide4Major Metabolic Functions of the Liver
Synthetic Function
Plasma proteins (albumin, globulins), cholesterol, triglycerides and lipoproteins
Detoxification and excretion
Ammonia to urea (urea cycle), bilirubin, cholesterol, drug metabolites
Storage Function
Vitamins A, D, E, K and B
12
Production of bile salts
Helps in digestion
Slide5Liver Function Tests (LFTs)
Noninvasive methods for screening of liver dysfunction
Help in identifying general types of disorder
Assess severity and allow prediction of outcome
Disease and treatment follow up
Slide6Liver Function Tests (LFTs)
Broadly classified as:
Tests to detect hepatic injury:
Mild or severe; acute or chronic
Nature of liver injury (hepatocellular or cholestasis)
Tests to assess hepatic function
Slide7Classification of LFTs
Group I: Markers of liver dysfunction
Serum bilirubin: total and conjugated
Urine: bile salts and
urobilinogen
Total protein, serum albumin and albumin/globulin ratio
Prothrombin
Time
Slide8Classification of LFTs
Group II: Markers of hepatocellular injury
Alanine aminotransferase (ALT)
Aspartate aminotransferase (AST)
Slide9Classification of LFTs
Group III: Markers of cholestasis
Alkaline phosphatase (ALP)
g
-
glutamyltransferase
(GGT)
Slide10Liver Enzymes
Slide11Aminotranferases
Aminotransferases or transaminases are a group of enzymes that catalyze the
interconversion
of amino acids and
ketoacids
(
oxoacids
) by transfer of amino group
The two aminotransferases of greatest clinical significance are:
Aspartate aminotransferase (AST), formerly termed glutamate oxaloacetate transaminase (GOT).
Alanine aminotransferase (ALT), formerly termed glutamate pyruvate transaminase (GPT
).
Pyridoxal
phosphate (P-5-P) is coenzyme
Slide12Aspartate aminotransferase (AST)
AST involved in the transfer of an amino group between aspartate and
-
ketoacids
.
Mohammed Laqqan
Slide13Clinical Significance
Aspartate aminotransferase (AST) is an enzyme found primarily in the
heart, liver
, and
muscle.
Additional AST is released into the circulation after injury or death of cells.
This test is one of several that are performed when there has been damage to the heart muscle, as in myocardial infarction, and in assessing liver damage.
Infants levels approximately twice the adult level, these decline to adult levels by approximately 6 months of age.
Mohammed Laqqan
Slide14Specimen
Collection
Specimen:
Serum, heparin plasma or EDTA plasma
Hemolysis should be avoided because it can dramatically increase serum AST concentrations
(RBCs contain 15 X the AST activity in serum)
Mohammed Laqqan
Slide15Assay for Enzyme activity
Measurement by
Karmen
method
A coupled reaction involving:
pyridoxal-5-phosphate (P-5-P)
and malate dehydrogenase (MDH)
at 37
o
C:
Decrease in absorbance at 340 nm is determined by continuous monitoring.
Aspartate +
-Ketoglutarate
Oxaloacetate + Glutamate
Oxaloacetate + NADH + H Malate + NAD
MD
AST
Mohammed Laqqan
Slide16Normal range: 8 – 20
U/L
Post
AMI
Rises 6 – 8 hours
Peaks at 24 hours
Returns to normal by day 5
AST levels are highest in acute hepatocellular disorders "viral hepatitis, cirrhosis.
Slide17Alanine Aminotransferase (ALT)
A
transferase
with enzymatic activity similar to AST
Converts alanine + α-
ketoglutarate
to pyruvate and glutamate
Mohammed Laqqan
Slide18Clinical Significance
It is found in the kidneys, heart, and skeletal muscle tissue but primarily in liver tissue.
The test is used mainly in the diagnosis of liver disease and to monitor the effects of hepatotoxic drugs.
Often higher than AST with liver damage and tend to remain elevated longer
(
More liver-specific than
AST)
Remains normal in AMI
Mohammed Laqqan
Slide19Specimen Collection
Specimen:
Serum, heparin plasma or EDTA plasma
Hemolysis should be avoided because it can increase serum ALT concentrations
(ALT in RBCs is roughly 5 X that of serum)
Mohammed Laqqan
Slide20Assay for enzyme activity
The most common method in use today for measurement of ALT activity utilizes a coupled enzymatic procedure for monitoring disappearance of NADH.
In this approach lactate dehydrogenase (LDH) and its required cofactors are added and catalyze the conversion of pyruvate to lactate
This causes simultaneous oxidation of reduced
nicotinamide
adenine dinucleotide (NADH).
The disappearance of NADH is followed
spectrophotometrically
(at 340 nm).
Alanine +
-Ketoglutarate
Pyruvate + Glutamate
Pyruvate + NADH + H Lactate + NAD
LD
ALT
Slide21Normal range (U/L):
Male
: 13-35
Female:
10-30
High serum levels in acute hepatitis (300-1000U/L)
Moderate elevation in alcoholic hepatitis (100-300U/L
)
Minor elevation in cirrhosis, hepatitis C and non-alcoholic
steatohepatitis
(NASH) (50-100U/L)
Slide22Levels of AST & ALT
AST is assessed along ALT in monitoring liver damage.
These two values normally exist in an approximately 1:1 ratio.
As a rough guide:
AST>ALT in:
alcoholic hepatitis and cirrhosis,
metastatic cancer of the liver
non-biliary cirrhosis,
while ALT>AST in:
viral and drug hepatitis,
chronic hepatitis C
and hepatic obstruction.
Mohammed Laqqan
Slide23Alkaline Phosphatase (ALP)
Phosphatases transfer a phosphate moiety from one group to a second, forming an alcohol and a second phosphate compound.
The optimal reaction pH for ALP is between 9 and 10 and varies with the buffer and substrate.
ALP requires Mg
2+
as an activator
Mohammed Laqqan
Slide24Isoenzymes
ALP exists as a number of
isoenzymes
Major are those found in Liver, bone, placenta, and then intestinal fraction
Electrophoresis for
isoenzyme
analysis
Liver
isoenzyme
(fastest)
Bone
isoenzyme
Placental
isoenzyme
Intestinal
isoenzyme
(slowest)
Immunochemical methods now available
Mohammed Laqqan
Slide25Clinical Significance
Alkaline phosphatase (ALP) is an enzyme found in the liver, bone, placenta, intestine, and kidneys
Primarily in the cells lining the biliary tract and in the osteoblasts involved in the formation of new bone.
ALP is normally excreted from the liver in the bile.
Increased ALP levels are found most commonly during:
periods of bone growth (as in children),
in various types of liver disease,
and in biliary obstruction.
Serum ALP activity primarily reflects changes in bone and liver function, even though higher ALP activities can be found in other organs.
Mohammed Laqqan
Slide26Specimen Collection
Blood should be drawn after a fast of at least 8 hours.
Serum or heparinized plasma.
Slight hemolysis is tolerable, but gross hemolysis should be avoided.
These increases may be caused by:
the release of ALP from complexes with lipoproteins,
It is best to analyze ALP specimens the same day they are drawn.
ALP is inhibited by metal-
complexing
anticoagulants; EDTA, oxalate, and citrate inhibit the enzyme by
complexing
Mg
2+
and should not be used.
Mohammed Laqqan
Slide27Assay for Enzyme activity
almost all assays for ALP employ p-
nitrophenyl
phosphate as the substrate.
Bowers and Combs method based on absorption of p-
nitrophenol
at 405 nm
At an alkaline pH,
p-
nitrophenyl
phosphate is colorless;
the product p-
nitrophenol
is intensely yellow
Slide28Normal range:
40 – 125 U/L
Slide29γ-
Glutamyltransferase
(GGT)
Transfers γ-
glutamyl
residue from γ-
glutamyl
peptides (usually glutathione) to amino acids, H
2
O and other small peptides
glutathione serves as the
γ
-
glutamyl
donor
Glutathione + Amino Acid
glutamyl
-peptide + L-
cysteinylglycine
High concentrations in liver tissue
Also in pancreas and kidney
GGT
Slide30Diagnostic Significance
Increased plasma GGT is associated with
Hepatobiliary
disease
Highest seen in biliary obstruction
Alcoholic cirrhosis
Used with ALP to differentiate between liver and bone diseases
Slide31Assay for enzyme activity
γ-
glutamyl
residue of γ
glutamyl
-p-
nitroanilide
is transferred to
glycylglycine
, releasing p-
nitroaniline
L-γ-
glutamyl
-p-
nitroanilide
+
glycylglycine
p-
nitroaniline
+ y-
glutamyl
glycylglycine
The rate of liberation of p-
nitroaniline
is directly related to the GGT activity in the sample and is quantitated by measuring the increase in absorbance at 405 nm.
GGT
Reference Range:
male, 6-45 U/L (37°C); female, 5-30 U/L (37°C)