Immunodiagnostics overview MCQs With Answer

Immunodiagnostics overview MCQs With Answer

This collection of multiple-choice questions is designed for M.Pharm students to reinforce and evaluate core concepts in immunodiagnostics. The quiz covers antigen–antibody interactions, assay formats (ELISA, RIA, CLIA, lateral flow, western blot, flow cytometry), analytical parameters (sensitivity, specificity, affinity, avidity), assay artifacts (hook/prozone effect, cross-reactivity, heterophile antibodies), controls, and modern multiplexing approaches. Questions emphasize practical understanding of assay design, interpretation of results, troubleshooting, and selection of appropriate methods for different analytes. Use these MCQs to test theoretical knowledge and to prepare for practical problem solving in immunotechnology and diagnostic assay development.

Q1. Which statement best distinguishes antibody affinity from avidity?

• Affinity refers to the cumulative binding strength of all interactions; avidity is the strength at a single binding site.
• Avidity is the strength of a single antigen–antibody interaction; affinity is the combined strength of multivalent interactions.
• Affinity is the strength of a single antigen–antibody interaction; avidity is the overall binding strength from multiple interactions.
• Affinity and avidity are synonymous and interchangeable terms.

Correct Answer: Affinity is the strength of a single antigen–antibody interaction; avidity is the overall binding strength from multiple interactions.

Q2. Which ELISA format is most appropriate for detecting a small hapten molecule (low molecular weight) in patient serum?

• Sandwich ELISA with two monoclonal antibodies
• Indirect ELISA using a labeled secondary antibody
• Competitive ELISA where labeled antigen competes with sample antigen
• Capture ELISA using immobilized antigen and labeled primary antibody

Correct Answer: Competitive ELISA where labeled antigen competes with sample antigen

Q3. In a sandwich ELISA, what is the primary role of the capture antibody?

• To compete with the analyte for binding sites on the plate
• To bind and immobilize the target analyte from the sample onto the solid phase
• To generate signal by conjugated enzyme activity
• To block non-specific binding sites on the plate

Correct Answer: To bind and immobilize the target analyte from the sample onto the solid phase

Q4. Which phenomenon causes falsely low measured concentrations at very high analyte levels in some immunoassays?

• Matrix effect
• Hook (prozone) effect
• Cross-reactivity
• High background signal

Correct Answer: Hook (prozone) effect

Q5. Which detection system provides the greatest sensitivity for low-abundance proteins in clinical assays?

• Colorimetric (TMB) with endpoint absorbance
• Radioimmunoassay (RIA) with gamma counting
• Chemiluminescent immunoassay (CLIA) with enhanced chemiluminescent substrate
• Direct fluorescent conjugate read by visual inspection

Correct Answer: Chemiluminescent immunoassay (CLIA) with enhanced chemiluminescent substrate

Q6. What is the main advantage of using monoclonal antibodies over polyclonal antibodies in diagnostic assays?

• Broader epitope recognition reduces specificity
• Higher batch-to-batch variability
• Consistent specificity for a single epitope and reduced cross-reactivity
• Lower production cost and faster development time

Correct Answer: Consistent specificity for a single epitope and reduced cross-reactivity

Q7. In a direct immunofluorescence assay, which component is labeled with a fluorophore?

• Secondary antibody only
• Antigen only
• Primary antibody that binds directly to the antigen
• Blocking reagent to reduce background

Correct Answer: Primary antibody that binds directly to the antigen

Q8. Which parameter describes the proportion of true positives correctly identified by a diagnostic test?

• Specificity
• Positive predictive value
• Sensitivity
• Negative predictive value

Correct Answer: Sensitivity

Q9. Which assay principle is based on measuring light emission produced by enzymatic conversion of a substrate to an excited-state intermediate?

• Colorimetric assay
• Fluorescent assay
• Chemiluminescent assay
• Radioimmunoassay

Correct Answer: Chemiluminescent assay

Q10. What is the primary reason to perform antigen retrieval in immunohistochemistry (IHC) on formalin-fixed paraffin-embedded tissues?

• To dehydrate tissue sections before staining
• To remove endogenous peroxidase activity
• To unmask or restore epitopes masked by cross-linking during fixation
• To block non-specific binding sites

Correct Answer: To unmask or restore epitopes masked by cross-linking during fixation

Q11. Which factor most directly affects the limit of detection (LOD) of an immunoassay?

• Affinity of the antibody for the analyte
• Volume of sample applied to the plate
• Color of microplate wells
• Number of wash steps only

Correct Answer: Affinity of the antibody for the analyte

Q12. Which of the following best explains heterophile antibody interference in immunoassays?

• Antibodies in the patient sample nonspecifically cross-link assay antibodies leading to false results
• Low analyte concentrations causing non-linear calibration curves
• Incomplete washing leading to high background
• Enzyme substrates degrading over time

Correct Answer: Antibodies in the patient sample nonspecifically cross-link assay antibodies leading to false results

Q13. In flow cytometry, what does side scatter (SSC) primarily reflect about a cell?

• Cell viability
• Cell size (volume)
• Internal complexity or granularity
• Surface antigen density

Correct Answer: Internal complexity or granularity

Q14. Which statement about competitive ELISA calibration curves is correct?

• Signal increases with increasing analyte concentration.
• Signal decreases with increasing analyte concentration.
• Signal is independent of analyte concentration.
• The curve is always linear across the entire range.

Correct Answer: Signal decreases with increasing analyte concentration.

Q15. Which blocking agent is commonly used to reduce non-specific protein binding on ELISA plates?

• SDS (sodium dodecyl sulfate)
• Bovine serum albumin (BSA)
• Hydrochloric acid
• Proteinase K

Correct Answer: Bovine serum albumin (BSA)

Q16. Which technique combines immunoassay specificity with molecular weight separation to confirm protein identity?

• ELISA with competitive format
• Immunohistochemistry
• Western blot (immunoblot)
• Direct immunofluorescence

Correct Answer: Western blot (immunoblot)

Q17. Which is a key advantage of multiplex bead-based immunoassays (e.g., Luminex) over singleplex ELISA?

• They require larger sample volumes per analyte.
• They can analyze multiple analytes simultaneously from a small volume.
• They are always less expensive than ELISAs.
• They eliminate the need for standard curves.

Correct Answer: They can analyze multiple analytes simultaneously from a small volume.

Q18. Why is signal amplification using secondary antibodies often used in indirect immunoassays?

• To decrease assay sensitivity intentionally
• To increase signal and sensitivity by allowing multiple labeled secondaries to bind each primary
• To block antigen–antibody interactions
• To remove unbound primary antibodies more effectively

Correct Answer: To increase signal and sensitivity by allowing multiple labeled secondaries to bind each primary

Q19. Which control is essential to detect non-specific binding of detection reagents in an immunoassay?

• Blank (no sample, no antibodies)
• Positive control containing high analyte concentration
• Negative control or isotype control lacking target antigen
• Enzyme substrate-only control

Correct Answer: Negative control or isotype control lacking target antigen

Q20. Which modification would most likely reduce cross-reactivity in an antibody-based diagnostic assay?

• Using lower stringency wash conditions
• Choosing polyclonal antibodies raised against whole-cell lysate
• Selecting or engineering monoclonal antibodies specific to unique epitope regions
• Increasing incubation temperature to extremes without optimization

Correct Answer: Selecting or engineering monoclonal antibodies specific to unique epitope regions

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