Serological Tests Prt1 Flashcards
Define
Tests to detect antigen or antibody in the samples of patients
Could be qualitative or quantitative
Define titter
Quantification of antibodies
What are serological test particularly useful in
▪️Diagnosis of multiple infectious diseases diagnosis of organisms which are difficult to be cultured
▪️diagnosis of slowly growing organisms stereotyping epidemic and pandemic infectious diseases
▪️mass screening for detection of infectious diseases such as hepatitis C
▪️blood grouping and cross matching ▪️detecting of auto antibodies that are involved in auto immune diseases
What is diagnosis of a recent infection confirmed by
Detection of IGM indicates a recent primary infection
Rising titer increases the ab level at least four hold between the serum obtain during the acute phase of the disease and that obtain at least 2 to 3 weeks later during the convalescent phase
High stationary titer if the titer of antibody is considerably higher than that found in the general population
What are the types of serological test
Agglutination reactions
precipitation reactions
antibody labeled assays
Describe the principle of agglutination reactions
▪️Formed of antigen antibody complexes in the form of visible particulate clumps
▪️Due to interaction between insoluble form of antigens and specific antibodies
▪️End point is observation of clumps emerging from antigen antibody complex formation
What are the two types of agglutination reactions
Slide agglutination test and tube agglutination test
Describe the slide agglutination test
▪️Agglutination reaction test performed on a slide
▪️Examples:blood grouping,
detection of bacterial antigen and stereotyping
▪️Done by mixing a drop of antigen antibody on a glass slide or a porcelain plate
▪️negative control should be added by mixing a drop of antigen with normal Saline to validate the results
Describe the tube agglutination test
▪️Performed in test tubes
▪️Examples:widal test for typhoid fever standard agglutination test for brucellosis
▪️Use for deduction of a specific antibody inpatient same with the presence of a constant amount of antigen
▪️Semi quantitative test to determine the antibodies titer in a given serum sample
▪️Consist of adding a fixed volume of antigen into test tubes containing serial dilutions of antibodies in normal saline
▪️A positive reaction is indicated by affirmation of visible clums after pre-determined period of incubation
What are the advantages of agglutination tests
Easy and quick to perform and sensitive
What are the disadvantages of agglutination tests
Susceptibility to negative reactions called by the prozone phenomenon and the reactions are at best semi-quantitive
What is the prozone phenomenon
Serious limitation of agglutination test
Happens when there is an excess of antibodies within which no reaction occurs in agglutination will be inhibited
Can be inhibited by using serial dilutions of serum to decrease the antibodies concentration
What are the examples of commercial agglutination reactions
Latex agglutination
Hemagglutination

Describe latex agglutination
Antigens are antibodies usually coat the surface of a carrier to detect the presence of a specific antibody or antigen of interest in the patient serum
Advantages are:
Large particle size of latex facilitates the visualization of the antigen antibody reaction
Rapid and easy test
Inexpensive
Relatively stable and not subject to cross-reactivity with other antibodies
Describe hemagglutination
Uses red blood cells as a biological carrier for bacterial antigens purified polysaccharides or proteins for detecting the presence of antibodies in a specimen
Two types
Direct: depends on the capability of some viruses to bind to rbcs resulting in agglutination
Indirect: coating of the surface of RBC’s with the antigen of interest to detect their corresponding ab and see whats in patient’s serum
