Immunologic Methods 1: Immunodiagnosis of Disease

Principles of Immunodiagnosis

• Immunodiagnosis is based on the interaction between antigens and antibodies to diagnose diseases.
• It assesses the presence of specific antibodies or antigens related to infectious agents or conditions.

Applications of Antigen Detection

• Commonly used for diagnosing infections by identifying the presence of pathogens directly in specimens.
• Useful in rapid testing scenarios, such as detecting viral infections like influenza or COVID-19.

Serology Testing

• Involves detecting antibodies in serum to assess immune response against pathogens.
• Typically used for diagnosing infections, autoimmune diseases, and blood grouping.

Specimen Collection and Transport

• The serology testing component responsible for specimen collection and transport is the pre-analytical phase.
• Proper handling and transportation of samples are crucial for accurate results.

Post-Analytical Potential Errors

• An example includes misinterpretation of assay results due to incorrect data reporting or documentation errors.
• Monitoring system failures or technician errors can also lead to false conclusions.

Usefulness of Serology Testing

• Particularly beneficial for organisms that are difficult to isolate via culture, such as certain viruses, spirochetes, and intracellular bacteria.
• Provides an alternative diagnostic method when traditional cultures are infeasible.

Significance of Positive IgM Without IgG

• Indicates a recent infection; IgM is the first antibody produced in response to an infection.
• Suggests acute phase of illness and a lack of past exposure or immunity to the pathogen.

Four-Fold Rise in Antibody Titer

• Indicates a significant increase in the immune response, suggesting active infection or recent exposure.
• Used as a diagnostic criterion in many infectious diseases.

Significance of the Zone of Equivalence

• The zone where antibody-antigen complexes form optimally, leading to visible precipitation in serological tests.
• Affects the sensitivity and specificity of the tests performed.

Common Causes of False Negative Results

• Occurs due to timing of specimen collection relative to infection (window period).
• Can also result from improper sample handling or storage temperature.

Compound Dilution in Serology Testing

• A compound dilution of 1:500 indicates the sample has been diluted up to 500 times from its original concentration.
• Used to quantify antibody levels in the patient’s serum.

Presence of IgG Without IgM in Serological Tests

• Indicates past infection or exposure; suggests previous immunity to the pathogen.
• May also represent an individual who has been vaccinated.

Secondary Antibody Response

• A rapid increase in IgG levels signifies a strong and quick immune response upon re-exposure to previously encountered pathogens.
• Indicates immunological memory and an effective response.

High Level of IgM Without IgG

• Suggests acute or recent infection; the immune system is actively responding.
• High IgM levels can correlate with the severity or stage of the infection.

Positive IgG Without IgM in Serological Tests

• Confirms previous infections or vaccinations, indicating established immunity.
• Suggests that the person is not currently infected.

Gradual Decline of IgG

• Indicates waning immunity or resolution of the infection.
• Natural progression after successful clearance of a pathogen from the system.

High Level of IgG Without IgM

• Reflects a past infection or vaccination; no current active infection.
• Suggests the body has developed long-term immunity against the pathogen.