Serological Tests Flashcards
Where are Antibodies and Antigens found?
Ab in serum
Ag in serum, body fluids, tissues
Define Test Specificity and Sensitivity
Specificity: true negative
Sensitivity: true positive
What is the Lattice formation?
Ab-Ag complex
Define Titer
The highest dilution of serum which gives an oservable reaction with Antigen
Specificity and sensitivity are directly related with ?
Affinity and avidity of the antibody
When does cross reactivity occur?
When two or more antigens share similar structural festures -> can have a bad influence on the test sensitivity and specificity
Types of serological testing
Type I: performed to detect antigen or antibody, soluble Ag and Ab is used
Type II: immunoassay test, performed within a solid phase, tests based on formation of Ag-Ab complex, identification of Ab isotypes
Where can agglutination tests be performed?
On slides, tubes or microtiter plates
Examples of direct agglutination tests
- hemagglutination/ Bacteria
- WRIGHT for brucellosis
- Gruber Widal for Salmonellosis
Indirect agglutination
Particles artificially covered with Ag
- RBS, polystyrene, latex, charcoal
Explain Coombs test
Direct coombs test performed with baby RBCs to detect Ab coating -> antihuman Ab used
Indirect coombs test performed with mothers serum to detect anti Rh Ab
Latex agglutination tests used for identification of which microorganisms?
H. Influenza, S. pneumonia, N. Meningitidis, S. aureus, C. Neoformans, C. Albicans, rubella virus
Explain precipitation
Ab can combine with soluble ag to form a visible precipitate
-> performed in splutions or in semisolid (agar) medium
Define turbidimetry
Measures turbidity by measuring the amount of light directly passing
Define nephelometry
Indirect measurment
Measures the scattered light
Neutralisation test principle
Serum is mixed with a known viral suspension -> if ab present in serum, they bind to the virus and prevent attachment -> when virus is added to cell culture -> can not replicate & cause cell death
Explain the ASO test
GAS produce Streptolysin O toxin which hemolyses RBCs
If there is an infection, -> Anti-streptolysin O Ab formation
RBC + Serum -> if there is no hemolysis, this means that the antibodies neutralized the toxin -> INFECTION
Explain Ag detection with ELISA Test
Ag specific Ab coated well -> add specimen -> wash to remove unbound components -> add enzyme conjugated secondary Ab -> wash -> add substrate
Explain Ab detection with ELISA Test
Ag coated well -> add Specimen -> wash -> add enzyme conjugated secondary Ab (bind to Fc) -> wash -> Substrate
Explain lateral flow assay
Sample containing Ag on ped -> Ag goes with capillary flow -> binds particle conjugated Ag specific Ab -> conjugated Ab based Ag captured by secondary Ag (test line) -> other particle conjugated Ab captured by Anti ab (control line)
