Transcript Interpretation Of Serology Tests In Selected Infections

Interpretation Of
Serology Tests In Selected Infections
Prof. Abdulkarim AlAska
Interpretation Of Serology Tests In Selected Infections
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Antibodies (ABs)
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IgM Acute infection
IgM cannot cross the placenta
IgG previous infection or exposure
IgG can cross the placenta.
IgG titre acute phase + Convalescence phase
(usually 2 weeks) is needed to confirm diagnosis
Sero – conversion >2 to 3 weeks but may be
delayed.
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False Negative Serologic Test
1.
2.
3.
4.
Immune system not intact
Delay in Antibody response (Lyme disease
- Legionnaire’s Disease)
Competition for Antigen binding site of
antibody)
IgM binds to the Antigen IgG site
IgG binds to the Antigen IgM site
Prozone Phenomena
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False Positive
1.
2.
3.
Cross reacting antibody
Cross reactivation of latent organism
(Influenza Virus A infection activate CMV
IgM – production
Presence of Rheumatoid factors
RF = IgM
RF + IgG =
Complexed
=
False positive organismspecific IgM Antibody
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Serological Diagnosis Of
Syphilis
I.
II.
III.
Specific Anti- treponemal Antibody
Anti – treponemal Antibody
Reagin Antibody (BFP)
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Serological Diagnosis Of
Syphilis
Test for specific Anti - treponemal Antibody
1. Absorbed fluorescent treponemal antibody
(FTA - ABs)
2. Treponema Pallidum Immobilization Test
(TPI)
A.
B.
C.
D.
Most sensitive
Utilize living Treponema maintained by passage in
rabbits testes.
Expensive
Potentially hazardous.
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Serological Diagnosis Of
Syphilis
3.
Treponema pallidum haemagglutination
(TPHA) test.
A.
B.
C.
D.
E.
Sheep, chicken or turkey RBCs. Sensitized by
attaching killed Treponema pallidum.
Agglutinate by presence ofantibody
Less sensitive than FTA – Abs
Less reliable in the diagnosis of primary syphilis.
Sometimes false positive
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Serological Tests Of Syphilis


Anti – treponemal Antibody
Anti-treponemal ABs group detected by
Reiter Protein Complement Fixation Test
(RPCFT)
A.
B.
C.
Appears later than specific ABs
Some syphilis patient do not produce the form
of ABs
Used is limited.
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Tests For Reagin Antibody
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A.
Biological False Positive Antibody (BFP) Reagin
Antibody: associated with other diseases (BFP)
Acute:
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B.
Chronic:
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Pneumonia
Vaccination with live attenuated viruses.
Malaria
Pregnancy
Leprosy – the only infection
Reagin titre falls rapidly with treatment
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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.
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Active Treponema Pallidum
Infection
Positive Specific Tests e.g. TPHA
Positive ( ≥1/ 32) of non-specific test
(VDRL)
1.
2.
•
•
•
TPI-T (Treponema Pallidum Immobilization
Test)
FTA –T (Fluorescent Treponema Test)
Sometimes needed for confirmation.
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Mycoplasma Pneumonia
Gradual onset, headache, fever, malaria,
most typically dry cough.
 Non respiratory:
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Meningitis
Encephalitis
Pancreatitis
Steven Johnson’s Syndrome
Sensori neural hearing loss
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Mycoplasma Pneumonia

ELISA:
More sensitive and specific
 Detect IgM, IgA
 IgM rise early after onset
 Peak is 1 – 4 weeks
 Decline in 2 – 4 months
 IgM rise in young patient (Good for diagnosis in
young patient)
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IgG and IgA
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IgG:
Rise slower.
 Remain elevated for long time.
 Rising titre diagnosis
 (2 samples at least 2 weeks apart indicate
current infection)
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IgA:
High level in elderly
 May be more useful than IgM in old patient.
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Legionella
Urinary
Antigen
Test
Description
Growing of
bacterium from
clinical sample, such
as sputum, on
specialized culture
media
Screening of urine
sample for the
presence of specific
legionella antigen
(cell markers)
80 %
80 %
Interpretation Of Serology Tests In Selected Infections
Specificity
Culture
Sensitivity
Technique
100 %
95 %
Processing
Time
3 – 5 days
Within hours
Disadvantages
Requires that
laboratory
technicians have
specialized training
and expertise.
Will only diagnose
infections with L.
pneumophila
serogroup 1
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Cont. Clinical Diagnosis
Direct
fluorescent
antibody
(DFA) stain
of sputum or
other sample
from lung
Visual screening of
sputum or other sample
from lung for legionella
bacteria; screening is
done under a UV
microscope, using
fluorescently – tagged
antibodies to “light up”
bacteria
33 –
70 %
Screening of blood sample
for antibodies to
legionella; generally
40 –
Antibody
requires comparison of
60%
testing
results from two samples,
(serology)
one collected during acute
illness and the other 2-8
weeks later
Interpretation Of Serology Tests In Selected Infections
Specificity
Description
Sensitivity
Technique
95 –
100 %
95 –
100 %
Processing
Time
Within hours
2-8 weeks
Disadvantages
Easy to miss bacterium on
microscope slide; results
difficult to interpret;
requires that laboratory
technicians have
specialized training and
expertise
Sensitivity is low; for
optimal results, requires
collection of second blood
sample.
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Legionella Urinary Antigen
Tests
(Simple, rapid)
(70 – 80 % sensitive)
( 80 – 100 % specific)
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I.
II.
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ELISA, needs machine
Paper Chromatography
(No instrument ,30 minutes)
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Serological Tests Used In The
Diagnosis Of Human Brucellosis
1.
2.
3.
4.
5.

Serum Agglutination Test (SAT)
2-Mercaptoethanol
Coomb’s Test
Microplate Agglutination Test
ELISA Test
OTHERS:
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Complement Fixation Test
Rose Bengal Test
Gel Precipitation
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1. SAT = STAT (Standard
Tube Agglutination Test)
IgM, IgG, IgA
 Prozone
 End – Point Agglutination
(1 / 80 ?, 1 / 160 ?, 1 / 320)
 Persisting Antibody up to 24 months.
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2. ME (Mercaptoethanol)
Remove IgM
 Persisting IgG + IgA is diagnostic for
persistent – relapsing of Brucellosis.
 Decrease IgG is prognostic of successful
outcome
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Brucellosis
A.
COOMB’S TEST
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B.
Detect non-agglutinating antibody (Adding
AHG)
MICROPLATE AGGLUTINATION
(Antigen + NaCl + AHG)
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Highly sensitive
End – Point agglutination not defined
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S. Typhi
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H Antibody  Non specific
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O Antibody  Most lab. ≥ 1 / 80
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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.
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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 .
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H Pylori
TEST
Antibody IgM,
IgG, IgA
Urea Breath
Test
Fecal Antigen
EFFECT OF
H2 ↓ DRUGS
ANTI -BIOTIC
REMARKS
NO
NO
Population
study
Past or current
infection
YES
YES
Active
Infection
YES
Active
Infection
+
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Toxoplasmosis IHA Test
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APPLICATION: To detect Toxoplasma
antibodies by indirect haemagglutination
test.
INTERPRETATION OF RESULTS:
Results will be reported as:
A.
B.
C.

Positive
Doubtful
Negative
Doubtful results should be retested within 2
weeks.
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Comments
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There is evidence that very early infectious and
those of infants under 1 year of age may not be
detected by TOXO IHA Test.
1.
2.
3.
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Titres of 1:64 to 1:128 are usually indicative of past
exposure, and can be the result of an asymptomatic
infection.
Titres of 1:256 are usually indicative of a recent
infection, not necessarily of a still active infection.
Titres of 1:512 and greater indicative of
Toxoplasmosis.
In ocular Toxoplasmosis, titres of antibodies may
be very low.
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Toxoplasma IgM Elisa
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APPLICATION: For measurement of the
IgM antibodies to toxoplasma gondii in
human serum and plasma to aid in the
diagnosis of primary infection.
INTERPRETATION OF RESULTS:
A.
B.
C.
Negative :
Equivocal :
Positive :
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< 0.500 (arbitrary units)
0.500 - 0.599
≥ 0.600.
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Comments

Transplacental transmission of the parasite
resulting in Congenital Toxoplasmosis can
occur during acute acquired maternal
infection. The risk of fetal infection is a
function of the time at which acute maternal
infection occurs during gestation. Maternal
infections acquired before conceptions
present very little, if any, risk to the fetus
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Comments (2)
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Prospective studies of pregnancies have
shown that prenatal diagnosis if infection
followed by prenatal therapy reduces the
frequency and Severity of Congenital
Toxoplasmosis.
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Comments (3)

Since persisting IgM levels may be detected
long after the onset of acquired infection, the
use of a single serological test result must
be used with caution in those cases when it
is critical to establish the time of infection.
This applies to the diagnosis of Acute T.
gondii infection acquired during pregnancy
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Leishmaniasis IHA
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Application: For detection of anti-leishmania
antibodies in serum.
Interpretation of Results:
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1.
2.
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The result is reported as follows:
If the reported titre is 1:128, send another sample after
2 weeks for re-testing.
Significant titres range from 1:256 to 1:12048.
Comments:
Low positive titres of 1:32 or more are a sign of
Leishmania infection (but does not indicate the
status of infection whether active or inactive).
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Echinococcus IHA
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1.
2.
Application:
For detection of anti
Echinococcus antibodies in human serum.
Interpretation of Results:
Positive agglutination is given by titres
ranging from 1:32 to 1:128.
Titres of 1:512 or higher are considered
significant for Echinococcosis.
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Schistosomiasis IHA
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Application: For detection of Schistosomia
antibodies in serum.
Specimen: Serum
Interpretation of Result:
The result is reported as follows:
1.
2.
If the reported titre is 1:128, may indicate
exposure.
Titre of patients suffering from schistosomiasis
range between 1:256 and 1:1024.
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Thank you ..
PROF. ABDULKARIM AL-ASKA, FACHARTZ
PROFESSOR & CONSULTANT IN INFECTIOUS DISEASES
INFECTIOUS DISEASES UNIT
DEPARTMENT OF MEDICINE
KING KHALID UNIVERSITY HOSPITAL
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