Competitive solid-phase enzyme immunoassay for measuring digoxin in serum

Area of Science:

• Clinical Chemistry
• Immunology
• Biochemistry

Background:

• Digoxin is a crucial medication for treating heart conditions, necessitating precise therapeutic drug monitoring.
• Existing digoxin immunoassays may face challenges with serum matrix effects and antibody performance.

Purpose of the Study:

• To develop and validate a novel enzyme immunoassay for serum digoxin quantification.
• To optimize the assay using Fab fragments for improved performance and reduced matrix interference.

Main Methods:

• A competitive enzyme immunoassay was developed using beta-galactosidase-labeled digoxin and anti-digoxin Fab fragments.
• Serum samples were incubated with reagents, followed by Sepharose-bound antibody separation.
• Unbound enzyme activity in the supernatant was measured to determine digoxin concentration.

Main Results:

• The optimized immunoassay buffer effectively minimized serum matrix effects.
• Immunoassays utilizing Fab fragments demonstrated superior displacement characteristics compared to intact antibodies.
• The assay showed excellent correlation (r=0.97) with the EMIT method in 110 clinical specimens.

Conclusions:

• This enzyme immunoassay provides a clinically useful and convenient method for serum digoxin measurement.
• The use of Fab fragments enhances assay performance, making it a viable alternative to existing digoxin immunoassays.