Serology.ppt

Serology
Principles and Interpretation
in Infectious diseases
Dr.T.V.Rao MD

Beginning of Serology
• Serology as a science began in 1901.
Austrian American immunologist Karl
Landsteiner (1868-1943) identified
groups of red blood cells as A, B, and O.
From that discovery came the recognition
that cells of all types, including blood cells,
cells of the body, and microorganisms
carry proteins and other molecules on their
surface that are recognized by cells of the
immune system.

Karl Landsteinar (1868-1943)
• An Austrian physician
by training,
Landsteiner played an
integral part in the
identification of blood
groups. He
demonstrated the
catastrophic effect of
transfusing with the
wrong type of blood,

Purpose of Serological Tests
• Serological tests may be performed for
diagnostic purposes when an infection is
suspected, in rheumatic illnesses, and in
many other situations, such as checking
an individual's blood type. Serology blood
tests help to diagnose patients with certain
immune deficiencies associated with the
lack of antibodies, such as X-linked
agammaglobulinemia.

Serology
• The branch of
laboratory medicine
that studies blood
serum for evidence of
infection and other
parameters by
evaluating antigen-
antibody reactions in
vitro

Serology
• Serology is the
scientific study of
blood serum. In
practice, the term
usually refers to the
diagnostic
identification of
antibodies in the
serum
We can detect
antigens too

Serology prerogative of
Microbiology
• It is rather curious that, although serum for
a multitude of constituents in biochemistry
and haematological laboratories, the term
serology has come to imply almost
exclusively the detection of antibodies in
serum for antibodies in infectious
diseases, and terminology has become
prerogative of microbiologists.

Immunology/ Serology?
Precipitation Reactions
• Capillary tube precipitation (Ring Test)
• Ouchterlony Double Diffusion (Immunodiffusion)
• Radialimmunodiffusion (RID)
• Immunoelectrophoresis (IEP)
• Rocket Electroimmunodiffusion (EID)
• Counterimmunoelectrophoresis (CIEP)
The above tests have moved to
Biochemistry

Terms used in evaluating test
methodology
• Sensitivity
–Analytical Sensitivity – ability of a
test to detect very small amounts of
a substance
–Clinical Sensitivity – ability of test
to give positive result if patient has
the disease (no false negative
results)

Specificity
• Analytical Specificity – ability of test to
detect substance without interference from
cross-reacting substances
• Clinical Specificity – ability of test to give
negative result if patient does not have
disease (no false positive results)

Affinity
• Affinity refers to the
strength of binding
between a single
antigenic determinant
and an individual
antibody combining
site.
• Affinity is the
equilibrium constant
that describes the
antigen-antibody
reaction

Affinity
• Antibody affinity is the strength of the
reaction between a single antigenic
determinant and a single combining site
on the antibody.
• It is the sum of the attractive and repulsive
forces operating between the antigenic
determinant and the combining site .

Avidity
• Avidity is a measure of
the overall strength of
binding of an antigen
with many antigenic
determinants and
multivalent antibodies
• Avidity is influenced by
both the valence of the
antibody and the valence
of the antigen.
• Avidity is more than the
sum of the individual
affinities.

Dilution
• Estimating the
antibody by
determining the
greatest degree to
which the serum may
be diluted without
losing the power to
given an observable
effect in a mixture
with specific antigen

Titer
• Different dilutions of
serum are tested in
mixture with a
constant amount of
antigen and greatest
reacting dilution is
taken as the measure
or Titer

Expression of Titers
• Expressed in term of the
was in which they are
made
• Dilution 1 in 8 is a
dilution made by mixing
one volume of serum
with seven volumes of
diluents (Normal Saline )
• Incorrect to express
dilution as 1/8

Common methods in creating
dilutions

Sero Conversion
• Seroconversion is the
development of
detectable specific
antibodies to
microorganisms in the
blood serum as a
result of infection or
immunization.

Sero reversion
• Seroreversion is the
opposite of
seroconversion. This
is when the tests can
no longer detect
antibodies or antigens
in a patient’s serum

Testing paired Samples
• Testing for infectious
diseases is performed on
acute and convalescent
specimens (about 2
weeks apart) Paired
sample.
• Must see 4-fold or 2-
tube rise in titre to be
clinically significant

Majority Diagnostic tests are
Serological tests
• There are several
serology techniques
that can be used
depending on the
antibodies being
studied. These
include: ELISA,
agglutination,
precipitation,
complement-fixation,
and fluorescent
antibodies.

Antigen and Antibody
reactions can be identified by
different methods

Precipitation
• Principle
– Soluble antigen + antibody (in proper proportions) –>
visible precipitate
– Lattice formation (antigen binds with Fab sites of 2
antibodies)
• Examples
– Double diffusion (Ouchterlony)
– Single diffusion (radial immunodiffusion)
– Imunoelectrphoresis
– Immunofixation

Agglutination
• Principle
– Particulate antigen + antibody –> clumping
– Lattice formation (antigen binds with Fab sites of 2
antibodies forming bridges between antigens)
• Examples
– Direct agglutination (Blood Bank)
– Passive Hemagglutination (treat RBC's with tannic
acid to allow adsorption of protein antigens)
– Passive latex agglutination (antigen attached to latex
particle)

Neutralization reactions
• Similar in principle and interpretation of results
• Antibody-binding
• Hemagglutination inhibition (serum antibody reacts with
known nonparticulate antigen –> binding occurs)
• Neutralization (antibody neutralizes toxin)
• After binding, antibody is not available to react in
indicator system
• Results:
• NO agglutination or NO hemolysis = positive reaction
• Agglutination or hemolysis = negative reaction (antibody
not bound in origin

• Generally, positive control samples used
in inhibition or neutralization tests show no
reaction and negative control samples
show a reaction (opposite of results in
direct agglutination testing)
• Example of inhibition: Hemagglutination
inhibition test for rubella
• Example of neutralization: antistreptolysin
O test (ASO)
Neutralization reactions

Complement fixation (CF)
• Antibody and antigen allowed to combine in
presence of complement
• If complement is fixed by specific antigen-
antibody reaction, it will be unable to combine
with indicator system
• Precautions
• Serum must be heat-activated
• Stored serum becomes anti-complementary
• Extensive QC/standardization required
• Only use for IgM antibodies

Imunoelectrphoresis (IEP)
Qualitative
• A serum sample is
electrophoresed through
an agar medium.
• A trough is cut in the agar
and filled with Ab.
• A precipitin arc is then
formed.
• Because Ag diffuses
radially and Ab from a
trough diffuses, the
reactants meet in optimal
proportions for
precipitation.

Serology can be done on various
speciemns
• Some serological tests are not limited to
blood serum, but can also be performed
on other bodily fluids such as semen and
saliva, which have (roughly) similar
properties to serum.
• Serological tests may also be used
forensically, generally to link a
perpetrator to a piece of evidence (e.g.,
linking a rapist to a semen sample).

Enzyme immunoassay
(EIA/ELISA)
• Sandwich technique”
• Monoclonal or polyclonal antibody adsorbed on solid
surface (bead or microtiter plate)
• Add patient serum; if antigen is present in serum, it binds
to antibody coated bead or plate
• Add excess labelled antibody (antibody conjugate);
forms antigen-antibody-labelled antibody “sandwich”
(antibody in conjugate is directed against another
epitope of antigen being tested)
• Add substrate, incubate, and read absorbance
• Washing required between each step
• Absorbance is directly proportional to antigen
concentration

ELISA methods takes over
• Enzyme-linked immunosorbent assay, also
called ELISA, enzyme immunoassay or EIA, is
a biochemical technique used mainly in
immunology to detect the presence of an
antibody or an antigen in a sample. The ELISA
has been used as a diagnostic tool in medicine
• Because the ELISA can be performed to
evaluate either the presence of antigen or the
presence of antibody in a sample

ELISA Most popular technological
advance in Laboratory Medicine
• ELISA methods can
detect any infectious
disease provided if
we have antibodies
and antigen to any
infection, enzyme or
any substance

Serology applications
in..
• HIV testing
• Serum HCG
(pregnancy)
• Tests for hepatitis
antigens and
antibodies
• Antibodies to bacteria
• Hepatitis Serology

Nephelometry
• Procedure
– Serum substance reacts with specific antisera and
forms insoluble complexes
– Light is passed through suspension
– Scattered (reflected) light is proportional to number of
insoluble complexes; compare to standards
• Examples
– Complement component concentration
– Antibody concentration (IgG, IgM, IgA, etc.)
• Immunofluorescence

Immunofluorescence
• Direct – add fluorescein-labeled antibody to
patient tissue, wash, and examine under
fluorescent microscope
• Indirect – add patient serum to tissue containing
known antigen, wash, add labeled antiglobulin,
wash, and examine under fluorescent
microscope
• Examples
– Testing for Antinuclear Antibodies (ANA)
– Fluorescent Treponemal Antibody Test (FTA-Abs)

Fluorescence polarization
immunoassay (FPIA)
• Principle
• Add reagent antibody and fluorescent-tagged antigen to
patient serum
• Positive test
– Antigen present in patient serum binds to reagent leaving most
tagged antigen unbound
– Unbound labeled antigens rotate quickly reducing amount of
polarized light produced
• Negative test
– If no antigen present in patient serum, tagged antigen binds to
reagent antibody
– Tagged antigen-antibody complexes rotate slowly giving off
increased polarized light

Flow cytometry
• Method of choice for T- and B-cell analysis (lymphocyte
phenotyping)
• Principle
• Incubate specimen with 1 or 2 monoclonal antibodies
tagged with fluorochrome
• Single cells pass through incident light of instrument
(laser) which excites fluorochrome and results in emitted
light of different wavelength
• Intensity of fluorescence measured to detect cells
possessing surface markers for the specific monoclonal
antibodies that were employed
• Forward light scatter indicates cell size or volume
• 90° side-scattered light indicates granula

Common uses Flow cytometry
• DNA analysis
• Reticulocyte counts
• Leukaemia/lymphoma
classification
• CD 4 cell estimations
in AIDS/HIV patients.

Other Applications of
agglutination tests in Serology
i. Determination of blood types or antibodies
to blood group antigens.
ii. To assess bacterial infections
e.g. A rise in titer of an antibody to a particular
bacterium indicates an infection with that
bacterial type. N.B. a fourfold rise in titer is
generally taken as a significant rise in antibody
titer.

Georges-Fernand-Isidor Widal
• Widal in 1896, and
Widal & Sicard in
1896 described the
Widal reaction, and
this test has proved
of value in cases
where positive
cultures have been
unobtainable

Widal test a Popular test in
diagnosis of Typhoid Fever
• The Widal test is a
presumptive
serological test for
Enteric fever or
Undulant fever. In
case of Salmonella
infections, it is a
demonstration of
agglutinating
antibodies against
antigens O-somatic and
H-flagellar in the blood.

Widal test is century old ,
Is it loosing importance ?
• In this reaction antibodies react with antigens on
the surface of particulate objects and cause the
objects to clump together, or agglutinate. These
reactions were the earliest to be adapted to
diagnostic laboratory. Widal test is used for
diagnosis of typhoid fever. This test, developed
by Georges Fernand I. Widal (French physician)
in 1896, is now supplemented by more
sophisticated procedures.

Widal test – A standard tube
agglutination test
• Test can be performed by the tube dilution
technique which permits, the assay of antibody
titre. In this, a constant amount of the antigen is
added to a series of tubes containing serum
dilutions. After mixing, the tubes are incubated at
a particular temperature and the highest dilution
of serum showing visible agglutination is
determined.

Agglutination how it appear after
reactivity
• O
agglutination
is granular
• H
agglutination
is loose and
floccular

Principle of the Test
• A classic example of the agglutination
reaction is seen in the widal test for
diagnosis of typhoid fever. In this test the
antibody content of the patient's serum, is
measured by adding a constant amount of
antigen (Salmonella typhi) to the serially
diluted serum.

Reading the Widal Test
• Read the results by viewing the tubes
under good light against the dark
background with x2 magnifying lens
• Do not shake tubes before reading the
results
• Read titers as greatest dilutions giving
visible agglutinations.
• Limiting agglutination is 1in 200 the titer is
200 not to be reported as 1/200.

Interpretation of Widal test
• Test results need to
be interpreted
carefully in the light of
past history of enteric
fever, typhoid
vaccination, general
level of antibodies in
the populations in
endemic areas of the
world.

Testing in Typhoid carriers
• Many known carriers of typhoid bacilli
possess antibody against the Vi
(virulence) antigen of S. typhi. This is a
surface antigen easily lost during
cultivation(Vi tires seem to correlate
better with the carrier state than do O
or H titres). For this reason, Felix et al.
suggested the use of Vi agglutination
for detection of carriers.

Importance of Vi antibodies
• Many known carriers of typhoid bacilli
possess antibody against the Vi
(virulence) antigen of S. typhi. This is a
surface antigen easily lost during
cultivation(Vi tires seem to correlate
better with the carrier state than do O
or H titres). For this reason, Felix et al.
suggested the use of Vi agglutination
for detection of carriers.

Prozone phenomenon in
Agglutination tests
Prozone effect - Occasionally, it is observed that
when the concentration of antibody is high (i.e.
lower dilutions), there is no agglutination and
then, as the sample is diluted, agglutination
occurs.
The lack of agglutination at high concentrations of
antibodies is called the prozone effect. Lack of
agglutination in the prozone is due to antibody
excess resulting in very small complexes that do
not clump to form visible agglutination

Causes Of False-positive Widal
Agglutination Tests
• Previous immunization with Salmonella
antigen.
• Cross-reaction with non – typhoidal
Salmonella.
• Variability and poorly standardized
commercial antigen preparation.
• Infection with malaria
• other Enterobacteriaceae charring the
same s-LPS .

Causes of Negative Widal
Agglutination Test
• The carrier state
• An inadequate inoculum of bacterial
antigen in the host to induce antibody
production
• Technical difficulty or errors in the
performance of the test.
• Previous antibiotic treatment
• Variability in the preparation of
commercial antigens.

Declining importance of Widal
test
• The value of the salmonella agglutination
tests has declined as the incidence of
typhoid fever has decreased, at least in
the developed world, the general use of
vaccines has increased, and ever
increasing -numbers of antigenically
related serotypes of Salmonella have been
recognised.

Serology - Importance of repeated
tests
Criteria for diagnosing Primary Infection
• 4 fold or more increase in titre of IgG or total antibody between
acute and convalescent sera
• Presence of IgM
• Seroconversion
• A single high titre of IgG (or total antibody) - very unreliable
Criteria for diagnosing Reinfection
• Four fold or more increase in titre of IgG or total
antibody between acute and convalescent sera
• Absence or slight increase in IgM

Typical Serological Profile After Acute
Infection
Note that during Reinfections, IgM may be absent or present at a low level transiently

Antigen – Antibody reactions
presenting with precipitation

Measurement of Precipitation by
Light
• Antigen-antibody complexes, when formed
at a high rate, will precipitate out of a
solution resulting in a turbid or cloudy
appearance.
• Turbidimetry measures the turbidity or
cloudiness of a solution by measuring
amount of light directly passing through a
solution.
• Nephelometry indirect measurement, measures amount
of light scattered by the antigen-antibody complexes.

Screening Tests for Syphilis
• Serologic methods are divided into two
classes. One class, the nontreponemal
tests, detects antibodies to lipoidal
antigens present in either the host or T.
pallidum; examples are the Venereal
Disease Research Laboratory and rapid
plasma reagin and tests.

Serological Diagnosis Of
Syphilis
I. Specific Anti-
treponemal
Antibody
II. Anti – treponemal
Antibody
III. Reagin Antibody
(VDRL and RPR)
Associated with higher
false positives

Indication for testing for Syphilis
Pregnant women
sexual contacts or
partners of patients
diagnosed with
syphilis
children born to
mothers with syphilis
patients with HIV
infection

Tests For Reagin Antibody
• A large numbers of tests for Reagin:
• VDRL (Venereal Diseases Reference Laboratory).
• RPR (Rapid Plasma Reagin)
• ART (Automated Reagin Test)
Good sensitive screening
Titre falls rapidly with treatment
• Reagin titre falls with treatment.

VDRL – A standard test for
Syphilis
• NONTREPONEMAL ANTIGEN TESTS.
Nontreponemal antigen tests are used as
screeners. They measure the presence of
reagin, which is an antibody formed in reaction
to syphilis. In the venereal disease research
laboratory (VDRL) test, a sample of the patient's
blood is mixed with cardiolipin and cholesterol. If
the mixture forms clumps or masses of matter,
the test is considered reactive or positive. The
serum sample can be diluted several times to
determine the concentration of reagin in the
patient's blood.

Screening tests should be
reported with cautions
• Reactivity in these tests generally
indicates host tissue damage that may not
be specific for syphilis. Because these
tests are easy and inexpensive to perform,
they are commonly used for screening,
and with proper clinical signs they are
suggestive of syphilis. The other class of
test, the Treponemal tests, uses specific
Treponemal antigens.

Combination of testes are
desirable
• Syphilis
serodiagnosis relies
on a combination of
nonspecific screening
tests (antilipoidal
antibodies) and
Treponema pallidum-
specific tests (anti-T.
pallidum antibodies).

Measurement of Precipitation by
Light
• Antigen-antibody complexes, when formed
at a high rate, will precipitate out of a
solution resulting in a turbid or cloudy
appearance.
• Turbidimetry measures the turbidity or
cloudiness of a solution by measuring
amount of light directly passing through a
solution.
• Nephelometry indirect measurement, measures amount of light
scattered by the antigen-antibody complexes.

Confirmation is warranted
• Confirmation of infection requires a reactive
Treponemal test. Examples of the Treponemal
tests are the microhemagglutination assay for
antibodies to T. pallidum and the fluorescent
treponemal antibody absorption test. These tests
are more expensive and complicated to perform
than the nontreponemal tests. On the horizon
are a number of direct antigen, enzyme-linked
immunosorbent assay, and PCR technique

Non reactive and Reactive VDRL
Tests

Rapid plasma reagin
• The rapid plasma
reagin (RPR) test
works on the same
principle as the
VDRL. It is available
as a kit. The patient's
serum is mixed with
cardiolipin on a
plastic-coated card
that can be examined
with the naked eye.

Agglutination++ RPR Agglutination+

Agglutination+: ve RPR Agglutination : -

Biological false positives
• Biological False Positive Antibody (BFP)
Reagin Antibody: associated with other
diseases (BFP)
A. Acute:
• Pneumonia
• Vaccination with live attenuated viruses.
• Malaria
• Pregnancy
B. Chronic:
• Leprosy – the only infection
• Reagin titer falls rapidly with treatment

Serological Diagnosis Of
Syphilis
Test for specific Anti - treponemal Antibody
1. Absorbed fluorescent treponemal
antibody (FTA - ABs)
2. Treponema Pallidum Immobilization Test
(TPI)
A. Most sensitive
B. Utilize living Treponema maintained by passage
in rabbits testes.
C. Expensive
D. Potentially hazardous.
E. Not done in the present contest as Technically demanding

Other Serological Methods in
Diagnosis Of Syphilis
Treponema pallidum haemagglutination
(TPHA) test.
A. Sheep, chicken or turkey RBCs. Sensitized by
attaching killed Treponema pallidum.
B. Agglutinate by presence of antibody
C. Less sensitive than FTA – Abs
D. Less reliable in the diagnosis of primary syphilis.
E. Sometimes false positive

Treponema Palladium
Hemagglutination test
TPHA

Other Serological Tests for
Syphilis
• Anti – Treponemal Antibody
• Anti-Treponemal ABs group detected by
Reiter Protein Complement Fixation Test
(RPCFT)
A. Appears later than specific ABs
B. Some syphilis patient do not produce the
form of ABs
C. Used is limited.

Detection by FTA-ABS IgG and
IgM
• In the FTA-ABS tests,
the patient's blood
serum is mixed with a
preparation that
prevents interference
from antibodies to
other treponemal
infections.

FTA abs IgG and IgM detection continues to be
a confirmatory test in diagnosis of Syphilis
• The test serum is added to a slide
containing T. pallidum. In a positive
reaction, syphilitic antibodies in the blood
coat the spirochetes on the slide. The slide
is then stained with fluorescein, which
causes the coated spirochetes to fluoresce
when the slide is viewed under ultraviolet
(UV) light..

Principle of Fluorescent Method

Active Treponema Pallidum
Infection
1. Positive Specific Tests e.g. TPHA
2. Positive ( ≥1/ 8) of non-specific test
(VDRL)
• TPI-T (Treponema Pallidum Immobilization
Test)
• FTA –T (Fluorescent Treponema Test)
• Sometimes needed for confirmation.

Emerging Methods in Diagnosis
of Syphilis
• Currently, ELISA,
Western blot, and
PCR testing are being
studied as additional
diagnostic tests,
particularly for
congenital syphilis
and neurosyphilis.

SPINAL FLUID TESTS in
Syphilis.
. Testing of cerebrospinal fluid (CSF) is an
important part of patient monitoring as well
as a diagnostic test. The VDRL and FTA-
ABS tests can be performed on CSF as
well as on blood. An abnormally high white
cell count and elevated protein levels in
the CSF, together with positive VDRL
results, suggest a possible diagnosis of
neurosyphilis.

CSF testing is indicated only in…
• CSF testing is not
used for routine
screening. It is used
most frequently for
infants with congenital
syphilis, HIV-positive
patients, and patients
of any age who are
not responding to
penicillin treatment.

Biological false reactive VDRL test among the
HIV infected patients
• Fewer reports on the biological false positive VDRL in
HIV individuals are documented. In this work, the author
studied the rate of biological false reactive VDRL among
the HIV-infected patients. Of interest, in this study, the
rate is significantly lower (by Fishers exact test) than a
recent previous report among prostitutes in India (10/94,
about 10.6 %). In the general population, the biological
false positive VDRL generally returns to negative within
14 weeks, without other clinical significance.
•
VirojWiwanitkit

Rickettsiae and Serology
• Rickettsiae is a genus of motile, Gram-negative,
non-spore forming, highly pleomorphic bacteria
that can present as cocci (0.1 μm in diameter),
rods (1–4 μm long) or thread-like (10 μm long).
Obligate intracellular parasites
• Because of this, Rickettsiae cannot live in
artificial nutrient environments and are grown
either in tissue or embryo cultures (typically,
chicken embryos are used).
• Still we have to dependent on Weil Felix test

Weil and Felix contribute for
testing
• In 1915, Weil and Felix showed that serum
of patients infected with any member of
the typhus group of diseases contains
agglutinins for one or more strains of O X
Proteus. In cases of typhus fever the
reaction usually appears before the sixth
day and reaches its height in the second
week.

Weil-Felix reaction – A
Heterophile agglutination Test
• A Weil-Felix reaction is a type of
agglutination test in which patients serum
is tested for agglutinins to O antigen of
certain non-motile Proteus and rickettsial
strains(OX19, OX2, OXk)
• OX19, OX2 are strains of Proteus vulgaris.
OXk is the strain of Proteus mirabilis.

Weil-Felix a Heterophile
agglutination test
• The agglutination reactions,
based on antigens common to
both organisms, determine the
presence and type of rickettsial
infection
• Because Rickettsiae are both
fastidious and hazardous, few
laboratories undertake their
isolation and diagnostic
identification
• Weil-Felix test that is based on
the cross-reactive antigens of
OX-19 and OX-2 strains of
Proteus vulgaris.

Interpretations in Weil-Felix
reaction
• Sera from endemic typhus agglutinate OX19,
OX2.
Tick borne spotted fever agglutinate OX19, OX2.
• Scrub Typhus agglutinate OXk strain
• Test is negative in rickettsialpox, trench fever
and Q-fever.
False positive reaction may occur in urinary or
other Proteus infections
Test may be negative in 50 percent scrub typhus

Weil-Felix test
indicated in when patients present
with rashes
• Test for diagnosis of
typhus and certain
other rickettsial
diseases. The blood
serum of a patient
with suspected
rickettsial disease is
tested against certain
strains of (OX-2, OX-
19, OX-K)..

Weil Felix test and Concentration
Camps

Weil-Felix test positivity saves
from Nazis
• In Poland, during World War II, where a pair of
quick-thinking doctors used a little-known
organism to keep the Nazis at bay.
The microorganisms is Proteus OX19. . Its one
remarkable feature is that human antibodies for
Proteus OX19 cross-react with the antibodies for
Ricksettia – the bacterium responsible for the
deadly disease typhus. Blood from a patient
infected with Proteus Ox19 will give a false-
positive in the most common typhus screening
method, the Weil-Felix test.

How they made Weil-Felix test
Positive
• While the Polish doctors could, and did,
inject a number of other people with
Proteus to induce positive Weil-Felix
results, an on-site Nazi medical team
could well have proved their undoing.
Fortunately, ingenuity and a good dose of
hospitality and alcohol prevented them
from being uncovered. (
From the British Medical Journal )

Other Emerging Serological
Tests

Co-agglutination
• Co agglutination is similar to the latex
agglutination technique for detecting
antigen (described above). Protein A, a
uniformly distributed cell wall component
of Staphylococcus aureus, is able to bind
to the Fc region of most IgG isotype
antibodies leaving the Fab region free to
interact with antigens present in the
applied specimens. The visible
agglutination of the S. Aureus particles
indicates the antigen-antibody reactions

Co agglutination Test
Agglutination test in
which inert particles
(latex beads or heat-
killed S aureus
Cowan 1 strain with
protein A) are coated
with antibody to any
of a variety of
antigens and then
used to detect the
antigen in specimens
or in isolated bacteria.

Chemiluminescence
• Chemiluminescence is
the emission of light
with limited emission
of heat
(luminescence), as
the result of a
chemical reaction.

Chemiluminescent
Immunoenzymatic Assay
• Process for the quantitative and qualitative
determination of antigens, antibodies and their
complexes by means of a chemiluminescing
labelling substance activated or excited to
chemiluminescence's by an analytical reagent.
By means of a serological reaction, initially an
antigen/antibody complex is formed which is
treated with a chemiluminescing conjugate
containing chemiluminescing triphenylmethane
dyes and the chemiluminescence of the
chemiluminescing complex formed is measured.

Recent testing Advances
• The ToRC IgG kit simultaneously detects
IgG class antibodies to Toxoplasmosis
gondii, rubella and cytomegalovirus
(CMV).
• The HSV-1 and HSV-2 IgG kit utilises
type-specific proteins to simultaneously
detect and differentiate IgG class
antibodies to the two most common
herpes subtypes, HSV-1 and HSV-2.

False Positive Serological Tests
1. Cross reacting antibody
2. Cross reactivation of latent organism (Influenza
Virus A infection activate CMV IgM –
production
3. Presence of Rheumatoid factors
RF = IgM
RF + IgG = Complexed
= False positive organism-
specific IgM Antibody

False Negative Serologic Test
1. Immune system not intact
2. Delay in Antibody response (Lyme
disease - Legionnaire’s Disease)
3. Competition for Antigen binding site of
antibody)
IgM binds to the Antigen IgG site
IgG binds to the Antigen IgM site
4. Prozone Phenomena

Usefulness of Serological
Results
• How useful a serological result is depends on
the individual virus.
• For example, for viruses such as rubella and
hepatitis A, the onset of clinical symptoms
coincide with the development of antibodies.
The detection of IgM or rising titers of IgG in
the serum of the patient would indicate active
disease.

Rota Virus - wether serology
useful ?
• However, many viruses
often produce clinical
disease before the
appearance of antibodies
such as respiratory and
diarrheal viruses. So in this
case, any serological
diagnosis would be
retrospective and therefore
will not be that useful.
• Acute presence of Antigen
is much useful in Diagnosis

Antibody detection is definitive
Diagnosis
• There are also viruses
which produce clinical
disease months or years
after seroconversion e.g.
HIV and rabies. In the
case of these viruses,
the mere presence of
antibody is sufficient to
make a definitive
diagnosis.

Problems with Serology
• Long period of time required for diagnosis for paired
acute and convalescent sera.
• Mild local infections such as HSV genitalis may not
produce a detectable humoral immune response.
• Extensive antigenic cross-reactivity between related
viruses e.g. HSV and VZV, Japanese B encephalitis and
Dengue, may lead to false positive results.

Problems with Serology
Other Health condtions interfere
• Immunocompromised patients often give a
reduced or absent humoral immune response.
• Patients with infectious mononucleosis and those
with connective tissue diseases such as SLE may
react non-specifically giving a false positive result.
• Patients given blood or blood products may give a
false positive result due to the transfer of antibody

Why Automate?
• Reduce variability and improve quality
• Reduce labor and test costs
• Improve workflow in the laboratory
• Avoid potential ergonomic issues

Automations
• One of the first successful
attempts to automate
• antibody tests was made
by Weitz (1967) at the
Lister Institute, London.
The apparatus developed
by Weitz (Fig. 3) allowed
the performance of up to
12 titrations in a single
operation, with even less
manipulation than that
required for a single test
done by a more
conventional technique.

Definitions (1)
• Quality Control - QC refers to the measures that must be included
during each assay run to verify that the test is working properly.
• Quality Assurance - QA is defined as the overall program that
ensures that the final results reported by the laboratory are correct.
• “The aim of quality control is simply to ensure that the results
generated by the test are correct. However, quality assurance is
concerned with much more: that the right test is carried out on the right
specimen, and that the right result and right interpretation is delivered
to the right person at the right time”

Definitions (2)
• Quality Assessment - quality assessment (also known as
proficiency testing) is a means to determine the quality of
the results generated by the laboratory. Quality assessment
is a challenge to the effectiveness of the QA and QC
programs.
• Quality Assessment may be external or internal, examples
of external programs include NEQAS, HKMTA, and Q-
probes.

Variables that affect the quality
of results
• The educational background and training of the
laboratory personnel
• The condition of the specimens
• The controls used in the test runs
• Reagents
• Equipment
• The interpretation of the results
• The transcription of results
• The reporting of results

Errors in measurement
• True value - this is an ideal concept which cannot be
achieved.
• Accepted true value - the value approximating the
true value, the difference between the two values is
negligible.
• Error - the discrepancy between the result of a
measurement and the true (or accepted true value).

Random Error
• An error which varies in an unpredictable manner, in magnitude
and sign, when a large number of measurements of the same
quantity are made under effectively identical conditions.
• Random errors create a characteristic spread of results for any test
method and cannot be accounted for by applying corrections.
Random errors are difficult to eliminate but repetition reduces the
influences of random errors.
• Examples of random errors include errors in pipetting and changes
in incubation period. Random errors can be minimized by training,
supervision and adherence to standard operating procedures.

Random Errors
x
x x
x x
True x x x x
Value x x x
x x x
x
x
x

Systematic Error
• An error which, in the course of a number of
measurements of the same value of a given quantity,
remains constant when measurements are made under the
same conditions, or varies according to a definite law
when conditions change.
• Systematic errors create a characteristic bias in the test
results and can be accounted for by applying a correction.
• Systematic errors may be induced by factors such as
variations in incubation temperature, blockage of plate
washer, change in the reagent batch or modifications in
testing method.

Systematic Errors
x
x x x x x x x
True x
Value

Internal Quality Control Program for
Serological Testing
An internal quality control program depend on the use of
internal quality control (IQC) specimens, Shewhart Control
Charts, and the use of statistical methods for interpretation.
Internal Quality Control Specimens
IQC specimens comprises either (1) in-house patient sera
(single or pooled clinical samples), or (2) international serum
standards with values within each clinically significant ranges.

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