1. Interpretation Of Serology Tests In Selected Infections
Prof. Abdulkarim AlAska

2. Antibodies (ABs) IgG previous infection or exposure
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
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
Interpretation Of Serology Tests In Selected Infections

4. False Positive 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 organism-specific IgM Antibody
Interpretation Of Serology Tests In Selected Infections

5. Serological Diagnosis Of Syphilis
Specific Anti- treponemal Antibody
Anti – treponemal Antibody
Reagin Antibody (BFP)
Interpretation Of Serology Tests In Selected Infections

6. Serological Diagnosis Of Syphilis
Test for specific Anti - treponemal Antibody
Absorbed fluorescent treponemal antibody (FTA - ABs)
Treponema Pallidum Immobilization Test (TPI)
Most sensitive
Utilize living Treponema maintained by passage in rabbits testes.
Expensive
Potentially hazardous.
Interpretation Of Serology Tests In Selected Infections

7. Serological Diagnosis Of Syphilis
Treponema pallidum haemagglutination (TPHA) test.
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
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)
Appears later than specific ABs
Some syphilis patient do not produce the form of ABs
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)
Acute:
Pneumonia
Vaccination with live attenuated viruses.
Malaria
Pregnancy
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
Positive Specific Tests e.g. TPHA
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: IgA: 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. Will only diagnose infections with L. pneumophila serogroup 1
Legionella
Disadvantages
Processing Time
Specificity
Sensitivity
Description
Technique
Requires that laboratory technicians have specialized training and expertise.
3 – 5 days
100 %
80 %
Growing of bacterium from clinical sample, such as sputum, on specialized culture media
Culture
Will only diagnose infections with L. pneumophila serogroup 1
Within hours
95 %
Screening of urine sample for the presence of specific legionella antigen (cell markers)
Urinary Antigen Test
Interpretation Of Serology Tests In Selected Infections

16. Cont. Clinical Diagnosis
Disadvantages
Processing Time
Specificity
Sensitivity
Description
Technique
Easy to miss bacterium on microscope slide; results difficult to interpret; requires that laboratory technicians have specialized training and expertise
Within hours
95 – 100 %
33 – 70 %
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
Direct fluorescent antibody (DFA) stain of sputum or other sample from lung
Sensitivity is low; for optimal results, requires collection of second blood sample.
2-8 weeks
40 – 60%
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
Antibody testing (serology)
Interpretation Of Serology Tests In Selected Infections

17. Legionella Urinary Antigen Tests
(Simple, rapid)
(70 – 80 % sensitive)
( 80 – 100 % specific)
ELISA, needs machine
Paper Chromatography
(No instrument ,30 minutes)
Interpretation Of Serology Tests In Selected Infections

18. Serological Tests Used In The Diagnosis Of Human Brucellosis
Serum Agglutination Test (SAT)
2-Mercaptoethanol
Coomb’s Test
Microplate Agglutination Test
ELISA Test
OTHERS:
Complement Fixation Test
Rose Bengal Test
Gel Precipitation
Interpretation Of Serology Tests In Selected Infections

19. 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. 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 COOMB’S TEST MICROPLATE AGGLUTINATION
Detect non-agglutinating antibody (Adding AHG)
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. Past or current infection
H Pylori
REMARKS
ANTI -BIOTIC
EFFECT OF H2 ↓ DRUGS
TEST
Population study
Past or current infection NO
Antibody IgM, IgG, IgA
Active Infection
YES
Urea Breath Test +
Fecal Antigen
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:
Positive
Doubtful
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.
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.
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:
Negative : < (arbitrary units)
Equivocal :
Positive : ≥
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:
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).
Interpretation Of Serology Tests In Selected Infections

33. Echinococcus IHA
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.
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:
If the reported titre is 1:128, may indicate exposure.
Titre of patients suffering from schistosomiasis range between 1:256 and 1:1024.
Interpretation Of Serology Tests In Selected Infections

35. Thank you .. PROF. ABDULKARIM AL-ASKA, FACHARTZ
PROFESSOR & CONSULTANT IN INFECTIOUS DISEASES
INFECTIOUS DISEASES UNIT
DEPARTMENT OF MEDICINE
KING KHALID UNIVERSITY HOSPITAL