micro 20.3 pt 5

Positive viral hemagglutination inhibition assay

Indicates that the patient's serum contains antibodies that inhibit viral hemagglutination.

Negative viral hemagglutination inhibition assay

Indicates that the patient's serum does not contain detectable antibodies capable of inhibiting the viral hemagglutination reaction.

Usefulness of hemagglutination inhibition assay

Measures whether antibodies can prevent viral particles from binding and agglutinating red blood cells.

Difference between viral hemagglutination inhibition assay and direct hemagglutination assay

Direct hemagglutination detects viruses that agglutinate RBCs, whereas hemagglutination inhibition detects antibodies that prevent that agglutination.

Presence of antiviral antibodies in hemagglutination inhibition assay

Antiviral antibodies bind the virus and prevent it from cross-linking RBCs, resulting in the RBCs settling to the bottom of the well.

Absence of antiviral antibodies in hemagglutination inhibition assay

The virus remains able to agglutinate RBCs, producing a diffuse layer of cells rather than a compact pellet.

Hemagglutination inhibition assay and antibody titer determination

Serial dilutions identify the highest dilution that still prevents hemagglutination.

Relationship between antibody concentration and hemagglutination inhibition

Higher concentrations of antiviral antibody generally produce stronger inhibition of hemagglutination.

Purpose of serial dilution in hemagglutination inhibition assay

To determine the amount or titer of antiviral antibody in the sample.

Application of viral hemagglutination inhibition assays

Determining whether a person has antibodies against a particular virus.

Utility of hemagglutination assays for influenza surveillance

Helps detect influenza viruses and measure antibodies against influenza strains.

Antibody titers in determining recent infections

A significant increase in antibody titer between acute and convalescent serum samples indicates a recent infection.

Acute-phase serum sample

A blood sample collected early during an infection.

Convalescent-phase serum sample

A blood sample collected later during recovery from an infection.

Paired serum samples in serological diagnosis

Comparing antibody levels between samples reveals a significant rise in antibody titer, supporting a recent infection.

Main principle of agglutination assays

Specific antigen-antibody interactions cross-link particles, producing visible clumping.

Determinants of agglutination reaction occurrence

The presence of the matching antigen and antibody in appropriate amounts.

Visibility of agglutination to the unaided eye

Antibody-mediated cross-linking produces large aggregates of cells or particles.

Difference between precipitation and agglutination

Precipitation involves soluble antigens forming insoluble complexes; agglutination involves antibodies clumping particulate antigens.

Difference between direct and indirect agglutination

Direct agglutination uses particles that naturally carry the target antigen; indirect uses particles artificially coated with antigen or antibody.

Difference between passive and reverse passive agglutination

Passive agglutination uses antigen-coated particles to detect antibodies; reverse passive uses antibody-coated particles to detect antigens.

Difference between coagglutination and latex agglutination

Coagglutination uses antibody-coated bacterial cells, commonly Staphylococcus aureus; latex agglutination uses antibody- or antigen-coated latex beads.

Agglutination assays in resource-limited settings

Simple, inexpensive, and require relatively little equipment, making them particularly useful.

Limitation of many agglutination assays

They may lack the sensitivity or specificity of more advanced diagnostic techniques.

Effect of previous vaccination on agglutination tests

Vaccination can produce antibodies that react with the test antigen, complicating the distinction between vaccination and infection.

Effect of previous infection on agglutination tests

Antibodies can remain in the blood post-infection, resulting in a positive test even when the infection is no longer active.

Main purpose of the direct Coombs' test

To detect antibodies or complement already attached to a person's RBCs.

Main purpose of the indirect Coombs' test

To detect free antibodies in serum that could react with RBC antigens.

Major clinical uses of agglutination assays

Blood typing, pathogen identification, serotyping, antibody detection, and diagnosis of infectious or immune-related conditions.

Central concept of agglutination assays

Antibodies cross-link particulate antigens, producing visible clumping that can be used to detect or measure specific antigens or antibodies.