Transcript liver-function-tests

D- LIVER FUNCTION TESTS
Introduction
Liver has to perform different kinds of biochemical,
synthetic and excretory functions
no single biochemical test can detect the global functions
of liver.
All laboratories usually employ a battery of tests for
initial detection and management of liver diseases
These tests are frequently termed “Liver function tests”.
Normal liver function
The various functions of the liver are carried out by the
liver cells or hepatocytes
a) Metabolic function
carbohydrate metabolism
 Gluconeogenesis
 Glycogenolysis
 Glycogenesis
protein metabolism, synthesis as well as degradation
lipid metabolism:
Cholesterol synthesis
Lipogenesis, the production of triglycerides (fats)
b) Storage functions
 glucose (in the form of glycogen),
Vitamins A , D, E, B12
 iron, and copper.
.
c) Synthetic function
 coagulation factors I (fibrinogen) , II
(prothrombin), V, VII, IX, X and XI, as well as
protein C, protein S and antithrombin
 produces and excretes bile (a yellowish liquid)
required for emulsifying fats.
Synthesizes albumin
d) Detoxification :
 ammonia to urea
Drugs and drug metabolites
e)Immunological - the reticuloendothelial
system of the liver contains many
immunologically active cells, acting as a 'sieve'
for antigens carried to it via the portal system.
Functions of liver
Uses of liver function tests
Screening : non-invasive yet sensitive
Pattern of disease : eg - differentiating between acute
viral hepatitis and various cholestatic disorders and
chronic liver disease. (CLD).
Assess severity and predict the outcome .
Follow up : and also helpful in evaluating response to
therapy
Liver function tests in practice
Markers of liver dysfunction
serum bilirubin ( excretory function)
urine bilirubin,urobilinogen and bile salts
Markers of synthetic dysfunction
Total protein, albumin, A/G ratio
Prothrombin time & INR
Detoxification markers
Blood ammonia
Exogeneous dye tests – BSP test
indocyanine green test
Markers of hepatocellular injury

Alanine aminotransferase ( ALT)
Aspartate transaminase (AST)

Alkaline phosphatase

Gamma glutamyl transferase

Leucine aminopeptidase

5’ nucleotidase
Other special tests
Ceruloplasmin ( Wilson’s disease)
Ferritin
Alpha-1-antitrypsin
Alphafetoprotein ( hepatocellular carcinoma)
Immunological tests
Antimitochondrial antibodies ( Pri biliary cirrhosis)
ANCA ( pri sclerosing cholangitis )
Bilirubin
Bilirubin is a breakdown product of haem (a part of
haemoglobin in red blood cells).
The liver is responsible for clearing the blood of
bilirubin.
Reference range : 0.2–0.8 mg/dL
Increased total bilirubin causes jaundice ( levels greater
than 2mg/dl)
Bilirubin ( contd)
Unconjugated (indirect)- insoluble
 ↑ in hemolysis, Gilbert syndrome
 Unconjugated hyperbilirubinemia when >80% of total
bilirubin is unconjugated
Conjugated (direct)- soluble
 ↑ in obstruction, cholestasis, cirrhosis, hepatitis, primary
biliary cirrhosis, etc.
 Conjug hyperbilirubinemia> 50% is conj bilirubin
Methods for bilirubin
1. Van den bergh reaction
2. Jendrassik- grof bilirubin method
3. Dry chemistry slide methods
 Methods for determination of serum bilirubin are based on
coupling of bilirubin pigments with diazo compounds to
form azobilirubin
 Conjugated bilirubin - immediate colour reaction (direct)
 Unconj bili – reaction on addition of alcohol/caffeine
benzoate ( indirect)
Urine bilirubin & urobilinogen
Urine bilirubin : only conjugated bilirubin is excreted in
urine
Urobilinogen:

increased in haemolytic anaemias

Decreased in hepatic diseases

Ref range – 0 – 4 mg/day

Lab determination is based on Ehlrich reaction
using para-dimethyl aminobenzaldehyde to give a red
colour
Bile acid assays
Are the final products of metabolism of cholesterol and
play a role in overall digestion of lipids
Serum concentration are microgram/ml amounts even
after a meal
Increased levels seen in liver diseases
Most helpful in differentiation of hepatobiliary disease
from congenital hyperbilirubinemia or hemolysis.
Lab methods: gas chromatography, Enzymatic methods
or immunoassays
Serum albumin
Albumin is the most significant protein synthesized by the liver and is
an indicator of overall function.
The half-life of albumin is approximately 20 days.
Albumin levels are decreased in chronic liver disease, such as cirrhosis
Normal albumin concentration does not rule out liver disease as an
acute condition may exist
Ref range 3.5 – 5 g/dl
• Poor marker of liver function- decreased by trauma, inflammatory
conditions, malnutrition
Prothrombin time and INR
 The liver is responsible for the production of coagulation factors
 The prothrombin time is the time it takes plasma to clot after
addition of tissue factor(obtained from animals)
 This measures the quality of the extrinsic pathway (greatly
affected by levels of factor VII in the body)
 poor factor VII synthesis (due to liver disease) may prolong the
PT.
 Normal : 12 – 14 seconds
•.
. The international normalized ratio (INR)
measures the speed of a particular pathway of
coagulation, comparing it to normal
Normal range for a healthy person is 0.9–1.3
high INR level INR=5 high chance of bleeding
 The INR will be increased only if the liver is so
damaged that synthesis of vitamin K-dependent
coagulation factors has been impaired;
 it is not a sensitive measure of liver function.
It is very important to normalize the INR before
operating on people with liver problems as they
could bleed
Grading Liver Function Using the Child-Turcotte Class
as Modified by Pugh
feature
0
1
Albumin >3.5 g/dl 2.83.5g/dl
Bilirubin <2 mg/dl 2 -3
mg/dl
2
<2.8
g/dl
>3 mg/dl
Prothro < 4 sec
mbin
time
4–6
sec
Ascites None
Controll Refracto
ed
ry
encepha None
lopathy
Controll refractor
ed
y
>6 sec
 The Child-Turcotte class, as
modified by Pugh, often known
simply as the "Child class," is
calculated by adding the points
as determined by the patient's
laboratory results: class A=0 to
1; class B=2 to 4; class C=5
and higher.
 The classes indicate severity of
liver dysfunction: class A is
associated with a good
prognosis, and class C is
associated with limited life
expectancy
Hepatocellular enzymes
Major diagnostic hepatocellular enzymes are
located at various sites in the hepatocyte giving rise
to different patterns of enzyme release depending on
the cause.
ALT & ASTc – cytosol
Released in membrane injury in viral or toxin
induced hepatitis.
ASTm – mitochondria , alc hepatitis
ALP & GGT – canalicular side of hepatocyte
Bile acids accumulate in cholestasis dissolve memb
fragments and release enzymes into plasma
Transaminases
Located in hepatocytes
 Released after hepatocellular injury
2 Forms
 AST ---ref range 10 – 35 IU/L
Non-specific to liver: heart, skeletal muscle, blood
 ALT ----- ref range 9 – 40 IU/L
More specific
Very high levels ( > 1000) – acute hepatitis
Moderate elevation ( 100-300) – alc hepatitis, wilson’s
disease, nonalcoholic cirrhosis
Mild elevation ( < 100) – chr viral hepatitis
AST:ALT ratio
Elevated in alcoholic disease (2: 1)
AST & ALT assays
 There are several variants of assays for
transaminases
 In one of them alanine for ALT or aspartate for
AST is added to yield glutamate.
 This is then coupled to enzyme glutamate
dehydrogenase ( indicator reaction) yeilding alpha
keto glutarate.
 In this reaction NAD is converted to NADH which
is measured as increase in absorbance at 340 nm
Aminotransferases
 normal in patients with
cirrhosis.
 uncomplicated alcoholic
hepatitis, the AST value is
rarely greater than 500 U per
L and is usually no more
than 200 to 300 U per L.
 The highest peak values
are found in patients with
acute ischemic or toxic liver
injury
Alkaline phosphatase
 Produced by biliary epithelial cells
Non-specific to liver: bone, intestine, placenta
 Elevations
Biliary duct obstruction
Primary biliary cirrhosis
Primary sclerosing cholangitis
Infiltrative liver disease
Highest elevationsI( more than 3 times) represent
obstructive disease
Ref range –30 -120 IU/L
Gammaglutamyl transpeptidase
Among the most sensitive tests in detecting early
hepatobiliary disease
More sensitive marker for cholestatic damage than ALP
may be elevated with even minor, sub-clinical levels of
liver dysfunction.
 It can also be helpful in identifying the cause of an
isolated elevation in ALP
Very sensitive in detecting chronic alc liver disease.
Leucine aminopeptidase and 5’nucleotidase
Used to increase the specificity of ALP enzyme for liver
dysfunction.
Not increased in bone diseases.
Lactate dehydrogenase: LD-5 isoenzyme is liver
specific indicates hepatocellular necrosis or metastatic
liver disease.
Detoxification and excretion markers
Ammonia : plasma ammonia concentration reflects
the liver’s ability to detoxify ammonia into urea and
excrete urea.
Mainly elevated in advanced liver disease
Useful in evaluating patients who are comatose or
with altered mental status
Most common lab determination is based on
enzymatic reaction using glutamate
dehydrogenase
Ref range : 15 – 45 µg/dl
Exogeneous dye tests :
Evaluate liver’s ability to transport exogeneous
substances into hepatocyte, metabolize and
finally excrete into bile.
Bromosulphopthalein test –a normally
functioning liver should remove > 95% of dye
in 45 min and retain only 5% in plasma
Determined spectrophotometrically
Indocyanine green test : dye is not
conjugated in the liver almost all of it is
recovered in the bile
Disappearence is direct function of blood flow
Disadv of dye tests : problems associated
with exogeneous substances so infrequently
performed.
Metabolic function tests
Lipid metabolism : hepatic disorders oten cause
derangements in lipoprotein metabolism.
In liver diseases there is deficiency of LCAT
and lipoprotein lipase
Resulting in reduced HDL, altered lipoprotein
distribution and hypertriglyceridemia.
Carbohydrate metabolism:
Glucose , galactose and fructose tolerance test
Limitations
Lack sensitivity:
The LFT may be normal in certain liver
diseases like cirrhosis, non cirrhotic portal fibrosis,
congenital hepatic fibrosis, etc.
Lack specificity :
not specific for any particular disease.
Serum albumin may be decreased in chronic disease
and also in nephrotic syndrome.
 Aminotransferases may be raised in cardiac
diseases and hepatic diseases.
Except for serum bile acids the LFT are not
specific for liver diseases and
 all the parameters may be elevated for
pathological processes outside the liver.
Thus, we see that LFT have certain advantages as
well as limitations at the same time.
 Thus, it is important to view them keeping the
clinical profile of the patient .
Jaundice
Jaundice (also known as icterus) is a yellowish
pigmentation of the skin, the conjunctival membranes
over the sclerae, and other mucous membranes
caused by hyperbilirubinemia (increased levels of
bilirubin in the blood).
Types of jaundice
Increased plasma concentrations of bilirubin (> 2 mg/dL) occurs when
there is an imbalance between its production and excretion
 Recognized clinically as jaundice
Prehepatic
 Results from excess production of
bilirubin (beyond the livers ability
to conjugate it) following hemolysis
 Excess RBC lysis the result of -
autoimmune disease; hemolytic
disease of the newborn
 structurally abnormal RBCs
(Sickle cell disease); or breakdown
of extravasated blood
 High plasma concentrations of
unconjugated bilirubin (normal
concentration ~0.5 mg/dL)
Hepatic
Impaired uptake,
conjugation, or secretion of
bilirubin
Reflects a generalized liver
(hepatocyte) dysfunction
In this case,
hyperbilirubinemia is usually
accompanied by other
abnormalities in biochemical
markers of liver function
Post hepatic
Caused by an obstruction of the
biliary tree
Plasma bilirubin is conjugated,
and other biliary metabolites, such
as bile acids accumulate in the
plasma
Characterized by pale colored
stools (absence of fecal bilirubin
or urobilin), and dark urine
(increased conjugated bilirubin)
In a complete obstruction, urobilin
is absent from the urine
Neonatal jaundice
 Common, particularly in premature infants
 Transient (resolves in the first 10 days)
 Due to immaturity of the enzymes involved in bilirubin conjugation
 High levels of unconjugated bilirubin are toxic to the newborn – due to its
hydrophobicity it can cross the blood-brain barrier and cause kernicterus
 Serum levels > 15mg/dl are usually seen
 Jaundice within the first 24 hrs of life or which takes longer then 10 days
to resolve is usually pathological and needs to be further investigated
Summary
Individual LFT results are not usually specific to a particular
disease; but the pattern of alteration can be more useful.
Abnormal liver function tests must be interpreted with
regard to clinical context and results of previous tests
 levels of derangements in LFTs are not always indicative of
the severity of the disease and clinical context is necessary
to determine the underlying aetiology
Take home message
 Despite the development of highly sensitive
laboratory tests, clinical assessment and
judgement remain paramount1