Immunodiagnostics and Serology

What is the primary focus of serology in vitro?

Which type of serological test detects the presence of antibodies in a sample?

What does a positive result in a direct serological test indicate?

What is the purpose of serial dilutions in serology?

Why is it important to understand antibody production dynamics in serology?

What is the term for the concentration of antibodies or antigens in a sample?

What is the significance of paired serology in diagnosis?

Which type of serological test is commonly used to diagnose infectious diseases?

What is the primary difference between IgG and IgM antibody levels?

What is the purpose of a cut-off in antibody levels?

Which of the following is true about the antibody levels at 0 days?

What is the advantage of using Cut-off 2?

What is the relationship between the time of infection and the antibody levels?

What is the purpose of using multiple cut-offs?

What is the purpose of Paired serology?

Immunodiagnostics

Study of antigen-antibody interactions in vitro
One of the most commonly used diagnostic tools
Used for infectious diseases, hormone detection, cancer, and autoimmunity
Basis of several different techniques
Most commonly performed on serum (blood) samples

Serology

Direct: detects the presence of the antigen in the sample, a positive result means infection
Indirect: detects the presence of antibodies or other products of the immune response in the sample, a positive result means exposure

Titers

Expresses the concentration of antibodies/antigens
Correlates with the highest dilution at which antibodies/antigens are still detectable

Understanding Antibody Production

Important for correct diagnosis
Choice of target antibody
Time of testing
Paired serology

Antibody Levels

IgM: early production, correlates with acute infection
IgG: later production, correlates with chronic infection
Cut-off values: sensitivity vs specificity
Paired serology: 1st test (acute phase) and 2nd test (convalescent phase)

Immunodiagnostic Techniques

Enzyme-Linked Immunosorbent Assay (ELISA)
- Uses enzyme-labeled antibodies or antigens to detect and/or measure analyte concentrations
- Variations: Direct ELISA, Indirect ELISA, Sandwich ELISA
Lateral or Bidirectional Flow Assays
- Qualitative or semi-quantitative
- Point-of-care testing
- Fast results
- No lab needed
Immunofluorescence
- Fluorescent-labeled antibodies
- Used on tissue or cells, on microscope slides
- Requires a fluorescent microscope to read results
Immunohistochemistry
- Used on frozen or formalin-fixed tissues
- In situ results
- Detects tissue proteins or pathogen antigens
Agglutination
- Reaction between antibody + particulate antigen or antibody + soluble antigen coated latex beads
Immunoprecipitation assays
- Precipitation of antigen-antibody complexes
- Exploits concentrations of antibody and antigen to measure relative quantities (titers)
- Solution-based and gel-based techniques

Immunodiagnostics is the study of antigen-antibody interactions in vitro, used for diagnosing infectious diseases, hormone detection, cancer, and autoimmunity. Serology is a branch of immunodiagnostics that detects the presence of antigens or antibodies in a sample.