Questions and Answers
What is the primary focus of serology in vitro?
Detecting antigens in a sample
Which type of serological test detects the presence of antibodies in a sample?
Indirect test
What does a positive result in a direct serological test indicate?
Presence of an antigen in the sample
What is the purpose of serial dilutions in serology?
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Why is it important to understand antibody production dynamics in serology?
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What is the term for the concentration of antibodies or antigens in a sample?
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What is the significance of paired serology in diagnosis?
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Which type of serological test is commonly used to diagnose infectious diseases?
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What is the primary difference between IgG and IgM antibody levels?
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What is the purpose of a cut-off in antibody levels?
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Which of the following is true about the antibody levels at 0 days?
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What is the advantage of using Cut-off 2?
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What is the relationship between the time of infection and the antibody levels?
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What is the purpose of using multiple cut-offs?
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What is the purpose of Paired serology?
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Study Notes
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
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