Serological Tests

Question 1

Where are Antibodies and Antigens found?

Answer 1

Ab in serum
Ag in serum, body fluids, tissues

Question 2

Define Test Specificity and Sensitivity

Answer 2

Specificity: true negative
Sensitivity: true positive

Question 3

What is the Lattice formation?

Answer 3

Ab-Ag complex

Question 4

Define Titer

Answer 4

The highest dilution of serum which gives an oservable reaction with Antigen

Question 5

Specificity and sensitivity are directly related with ?

Answer 5

Affinity and avidity of the antibody

Question 6

When does cross reactivity occur?

Answer 6

When two or more antigens share similar structural festures -> can have a bad influence on the test sensitivity and specificity

Question 7

Types of serological testing

Answer 7

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

Question 8

Where can agglutination tests be performed?

Answer 8

On slides, tubes or microtiter plates

Question 9

Examples of direct agglutination tests

Answer 9

• hemagglutination/ Bacteria
• WRIGHT for brucellosis
• Gruber Widal for Salmonellosis

Question 10

Indirect agglutination

Answer 10

Particles artificially covered with Ag
- RBS, polystyrene, latex, charcoal

Question 11

Explain Coombs test

Answer 11

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

Question 12

Latex agglutination tests used for identification of which microorganisms?

Answer 12

H. Influenza, S. pneumonia, N. Meningitidis, S. aureus, C. Neoformans, C. Albicans, rubella virus

Question 13

Explain precipitation

Answer 13

Ab can combine with soluble ag to form a visible precipitate
-> performed in splutions or in semisolid (agar) medium

Question 14

Define turbidimetry

Answer 14

Measures turbidity by measuring the amount of light directly passing

Question 15

Define nephelometry

Answer 15

Indirect measurment

Measures the scattered light

Question 16

Neutralisation test principle

Answer 16

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

Question 17

Explain the ASO test

Answer 17

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

Question 18

Explain Ag detection with ELISA Test

Answer 18

Ag specific Ab coated well -> add specimen -> wash to remove unbound components -> add enzyme conjugated secondary Ab -> wash -> add substrate

Question 19

Explain Ab detection with ELISA Test

Answer 19

Ag coated well -> add Specimen -> wash -> add enzyme conjugated secondary Ab (bind to Fc) -> wash -> Substrate

Question 20

Explain lateral flow assay

Answer 20

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)