Competitive solid-phase enzyme immunoassay for measuring digoxin in serum.
In this clinically useful enzyme immunoassay of digoxin in serum, we mix sample, beta-galactosidase-labeled digoxin, and anti-digoxin Fab fragments for 30 min at room temperature, then use Sepharose-bound second antibody for phase separation, and measure the unbound enzyme activity directly in the supernate of the equilibrium reaction mixture. The immunoassay buffer--phosphate-buffered isotonic saline with added rabbit globulin (4 g/L), hydrolyzed gelatin (2 g/L), Brij 96 detergent (5 g/L), glycerol (0.25 mol/L), and N-acetyl-8-anilinonaphthalene-1-sulfonic acid (2 mmol/L)--minimizes serum matrix effects for convenient measuring of unbound enzyme--digoxin conjugate. The immunoassay developed with Fab fragments has better displacement characteristics than that with intact antibody. Performance of the assay compares favorably with that of other manual digoxin immunoassays; in comparison studies with EMIT involving 110 clinical specimens, the coefficient of correlation was 0.97.
D000917:Antibody Formation; D000918:Antibody Specificity; D002021:Buffers; D004077:Digoxin / Q000097:blood* / Q000276:immunology; D005696:Galactosidases / Q000097:blood / Q000276:immunology; D006801:Humans; D007124:Immunoenzyme Techniques; D007140:Immunoglobulin Fab Fragments; D013696:Temperature
D002021:Buffers; D007140:Immunoglobulin Fab Fragments; D004077:Digoxin; D005696:Galactosidases