ELISA for antibody measurement: aspects related to data expression

Area of Science:

• Immunology
• Analytical Chemistry
• Biotechnology

Background:

• Enzyme-linked immunosorbent assay (ELISA) is widely used for detecting specific antibodies, such as antitoxoplasma IgG.
• Accurate quantification and consistent reporting of ELISA results are crucial for reliable diagnostics and research.
• Different methods exist for expressing ELISA results, each with potential limitations.

Purpose of the Study:

• To evaluate and compare three distinct methods for expressing analytical results from an ELISA for antitoxoplasma IgG.
• To assess the stability and linearity of these reporting modes under varying assay conditions.
• To determine the most reliable method for consistent and normalized quantification of antibody activity.

Main Methods:

• An ELISA for antitoxoplasma IgG was performed using antigen-coated polystyrene beads and enzyme-conjugated detection systems.
• Analytical results were expressed using three modes: end-point antibody titre, untransformed absorbance reading at a single dilution, and antibody-activity units derived from a calibration curve.
• Data were evaluated based on stability against assay design changes and experimental variability, and linearity of response with positive serum dilutions.

Main Results:

• Single absorbance readings show trends but exhibit significant variability and lack parallelism with antibody activity.
• Antibody titration offers parallelism but is impractical due to cost and labor, and suffers from reliability issues.
• Expressing results in antibody-activity units, derived from a reference scale, effectively eliminates systematic errors and ensures analytical consistency.

Conclusions:

• Antibody-activity units provide a robust and consistent method for quantifying antitoxoplasma IgG levels.
• This approach is essential for normalizing results across different runs, laboratories, and assay methods.
• The use of antibody-activity units is mandatory for reliable inter-laboratory and inter-method comparisons in diagnostic testing.