Interpretation Of Serology Tests In Selected Infections Prof. Abdulkarim AlAska

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

S. Typhi H Antibody  Non specific O Antibody  Most lab. ≥ 1 / 80 Interpretation Of Serology Tests In Selected Infections

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

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

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

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

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

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 : < 0.500 (arbitrary units) Equivocal : 0.500 - 0.599 Positive : ≥ 0.600. Interpretation Of Serology Tests In Selected Infections

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

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

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

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

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

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

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