Enzyme Immunoassays (EIA) Formats Immunology Review 392
METHOD
EIA
Enzyme-linked
immunosorbent
assay (ELISA)
Sandwich ELISA
or capture assay
OTHER
Original EIA. Used to measure small
relatively pure ags, e.g., insulin,
estrogen.
Used to detect abs to viruses, e.g.,
HIV, HAV, HCV, EBV.
Ags must have multiple determinants.
Used to measure Igs, hormones, pro-
teins & detect tumor markers, viruses,
parasites, fungi. High concentration of
ag can cause hook effect. Too much ag
for binding sites so undiluted sample
has lower absorbance than dilutions.
DESCRIPTION
Heterogeneous,
competitive, direct
Heterogeneous,
noncompetitive,
indirect
Heterogeneous,
noncompetitive,
indirect
PRINCIPLE
Enzyme-labeled ligand & unlabeled patient
ligand compete for binding sites on ab at-
tached to solid phase. Free labeled ligand re-
moved by washing. Substrate added. Color
inversely proportional to concentration of
ligand in specimen.
Ag attached to solid phase. Ab in specimen
attaches. Unbound ab removed by washing.
Enzyme-labeled antiglobulin added. At-
taches to ab on solid phase. Substrate added.
Color directly proportional to ab concentra-
tion. More sensitive than competitive EIA.
One of most common immunoassays.
Ab attached to solid phase. Ag in specimen
attaches. Enzyme-labeled ab added, at-
taches to different determinant. Enzymatic
activity directly proportional to amount of ag
in sample.
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