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

Interpretation Of Serology Tests In Selected Infections 1

Interpretation Of Serology Tests In Selected Infections

Prof. Abdulkarim AlAska


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.


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


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


Serological Diagnosis Of Syphilis

I. Specific Anti- treponemal Antibody

II. Anti – treponemal Antibody

III. Reagin Antibody (BFP)



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.



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


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.


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


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.


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.


Mycoplasma Pneumonia

Gradual onset, headache, fever, malaria, most typically dry cough.

Non respiratory: Meningitis Encephalitis Pancreatitis Steven Johnson’s Syndrome Sensori neural hearing loss


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)


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.


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


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.


Legionella Urinary Antigen Tests

(Simple, rapid) (70 – 80 % sensitive) ( 80 – 100 % specific)

I. ELISA, needs machine

II. Paper Chromatography (No instrument ,30 minutes)


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


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.


2. ME (Mercaptoethanol)

Remove IgM Persisting IgG + IgA is diagnostic for

persistent – relapsing of Brucellosis. Decrease IgG is prognostic of successful

outcome


Brucellosis

A. COOMB’S TEST Detect non-agglutinating antibody (Adding

AHG)

B. MICROPLATE AGGLUTINATION

(Antigen + NaCl + AHG) Highly sensitive End – Point agglutination not defined


S. Typhi

H Antibody Non specific

O Antibody Most lab. ≥ 1 / 80


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.


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 .


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


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.


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.


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.


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


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.


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


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).


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.


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.


Thank you ..PROF. ABDULKARIM AL-ASKA, FACHARTZ

PROFESSOR & CONSULTANT IN INFECTIOUS DISEASESINFECTIOUS DISEASES UNITDEPARTMENT OF MEDICINE

KING KHALID UNIVERSITY HOSPITAL

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