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Interpretation Of Serology Tests In Selected Infections 1
Interpretation Of Serology Tests In Selected Infections
Prof. Abdulkarim AlAska
Interpretation Of Serology Tests In Selected Infections 2
Antibodies (ABs)
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.
Interpretation Of Serology Tests In Selected Infections 3
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
Interpretation Of Serology Tests In Selected Infections 4
False Positive
1. Cross reacting antibody2. Cross reactivation of latent organism
(Influenza Virus A infection activate CMV IgM – production
3. Presence of Rheumatoid factorsRF = IgM RF + IgG = Complexed
= False positive organism-specific IgM Antibody
Interpretation Of Serology Tests In Selected Infections 5
Serological Diagnosis Of Syphilis
I. Specific Anti- treponemal Antibody
II. Anti – treponemal Antibody
III. Reagin Antibody (BFP)
Interpretation Of Serology Tests In Selected Infections 6
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.
Interpretation Of Serology Tests In Selected Infections 7
Serological Diagnosis Of Syphilis
3. Treponema pallidum haemagglutination (TPHA) test.
A. Sheep, chicken or turkey RBCs. Sensitized by attaching killed Treponema pallidum.
B. Agglutinate by presence ofantibody
C. Less sensitive than FTA – Abs
D. Less reliable in the diagnosis of primary syphilis.
E. Sometimes false positive
Interpretation Of Serology Tests In Selected Infections 8
Serological Tests Of 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.
Interpretation Of Serology Tests In Selected Infections 9
Tests For Reagin Antibody
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 titre falls rapidly with treatment
Interpretation Of Serology Tests In Selected Infections 10
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.
Interpretation Of Serology Tests In Selected Infections 11
Active Treponema Pallidum Infection
1. Positive Specific Tests e.g. TPHA
2. Positive ( ≥1/ 32) of non-specific test (VDRL)
• TPI-T (Treponema Pallidum Immobilization Test)
• FTA –T (Fluorescent Treponema Test)• Sometimes needed for confirmation.
Interpretation Of Serology Tests In Selected Infections 12
Mycoplasma Pneumonia
Gradual onset, headache, fever, malaria, most typically dry cough.
Non respiratory: Meningitis Encephalitis Pancreatitis Steven Johnson’s Syndrome Sensori neural hearing loss
Interpretation Of Serology Tests In Selected Infections 13
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)
Interpretation Of Serology Tests In Selected Infections 14
IgG and IgA
IgG: Rise slower. Remain elevated for long time. Rising titre diagnosis (2 samples at least 2 weeks apart indicate
current infection)
IgA: High level in elderly May be more useful than IgM in old patient.
Interpretation Of Serology Tests In Selected Infections 15
Legionella
TechniqueDescription
Sen
sitivity
Sp
ecificity
Processing Time
Disadvantages
Culture
Growing of bacterium from
clinical sample, such as sputum, on
specialized culture media
80 %100 %3 – 5 days
Requires that laboratory
technicians have specialized training
and expertise.
Urinary Antigen
Test
Screening of urine sample for the
presence of specific legionella antigen
(cell markers)
80 %95 %Within hours
Will only diagnose infections with L.
pneumophila serogroup 1
Interpretation Of Serology Tests In Selected Infections 16
Cont. Clinical Diagnosis
TechniqueDescription
Sen
sitivity
Sp
ecificityProcessing
TimeDisadvantages
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 %
95 – 100 %
Within hours
Easy to miss bacterium on microscope slide; results
difficult to interpret; requires that laboratory
technicians have specialized training and
expertise
Antibody testing
(serology)
Screening of blood sample for antibodies to
legionella; generally requires comparison of
results from two samples, one collected during acute illness and the other 2-8
weeks later
40 – 60%
95 – 100 %
2-8 weeksSensitivity is low; for
optimal results, requires collection of second blood
sample.
Interpretation Of Serology Tests In Selected Infections 17
Legionella Urinary Antigen Tests
(Simple, rapid) (70 – 80 % sensitive) ( 80 – 100 % specific)
I. ELISA, needs machine
II. Paper Chromatography (No instrument ,30 minutes)
Interpretation Of Serology Tests In Selected Infections 18
Serological Tests Used In The Diagnosis Of Human Brucellosis
1. Serum Agglutination Test (SAT)
2. 2-Mercaptoethanol
3. Coomb’s Test
4. Microplate Agglutination Test
5. ELISA Test OTHERS:
Complement Fixation Test Rose Bengal Test Gel Precipitation
Interpretation Of Serology Tests In Selected Infections 19
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.
Interpretation Of Serology Tests In Selected Infections 20
2. ME (Mercaptoethanol)
Remove IgM Persisting IgG + IgA is diagnostic for
persistent – relapsing of Brucellosis. Decrease IgG is prognostic of successful
outcome
Interpretation Of Serology Tests In Selected Infections 21
Brucellosis
A. COOMB’S TEST Detect non-agglutinating antibody (Adding
AHG)
B. MICROPLATE AGGLUTINATION
(Antigen + NaCl + AHG) Highly sensitive End – Point agglutination not defined
Interpretation Of Serology Tests In Selected Infections 22
S. Typhi
H Antibody Non specific
O Antibody Most lab. ≥ 1 / 80
Interpretation Of Serology Tests In Selected Infections 23
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.
Interpretation Of Serology Tests In Selected Infections 24
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 .
Interpretation Of Serology Tests In Selected Infections 25
H Pylori
TESTEFFECT OF H2 ↓ DRUGS
ANTI -BIOTICREMARKS
Antibody IgM, IgG, IgANONO
Population study
Past or current infection
Urea Breath Test
YESYESActive
Infection
Fecal Antigen+
YESActive
Infection
Interpretation Of Serology Tests In Selected Infections 26
Toxoplasmosis IHA Test
APPLICATION: To detect Toxoplasma antibodies by indirect haemagglutination test.
INTERPRETATION OF RESULTS: Results will be reported as:
A. PositiveB. DoubtfulC. Negative
Doubtful results should be retested within 2 weeks.
Interpretation Of Serology Tests In Selected Infections 27
Comments
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. Titres of 1:64 to 1:128 are usually indicative of past
exposure, and can be the result of an asymptomatic infection.
2. Titres of 1:256 are usually indicative of a recent infection, not necessarily of a still active infection.
3. Titres of 1:512 and greater indicative of Toxoplasmosis.
In ocular Toxoplasmosis, titres of antibodies may be very low.
Interpretation Of Serology Tests In Selected Infections 28
Toxoplasma IgM Elisa
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. Negative : < 0.500 (arbitrary units)
B. Equivocal : 0.500 - 0.599
C. Positive : ≥ 0.600.
Interpretation Of Serology Tests In Selected Infections 29
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
Interpretation Of Serology Tests In Selected Infections 30
Comments (2)
Prospective studies of pregnancies have shown that prenatal diagnosis if infection followed by prenatal therapy reduces the frequency and Severity of Congenital Toxoplasmosis.
Interpretation Of Serology Tests In Selected Infections 31
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
Interpretation Of Serology Tests In Selected Infections 32
Leishmaniasis IHA
Application: For detection of anti-leishmania antibodies in serum.
Interpretation of Results: The result is reported as follows:1. If the reported titre is 1:128, send another sample after
2 weeks for re-testing.2. 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).
Interpretation Of Serology Tests In Selected Infections 33
Echinococcus IHA
Application: For detection of anti Echinococcus antibodies in human serum.
Interpretation of Results:
1. Positive agglutination is given by titres ranging from 1:32 to 1:128.
2. Titres of 1:512 or higher are considered significant for Echinococcosis.
Interpretation Of Serology Tests In Selected Infections 34
Schistosomiasis IHA
Application: For detection of Schistosomia antibodies in serum.
Specimen: Serum Interpretation of Result:
The result is reported as follows:1. If the reported titre is 1:128, may indicate
exposure.
2. Titre of patients suffering from schistosomiasis range between 1:256 and 1:1024.