EMIT (Enzyme-Multiplied Immunoassay Technique)
Definition
A homogeneous competitive immunoassay in which drug in the sample competes with enzyme-labelled drug conjugate for antibody binding sites. Free enzyme-labelled conjugate remains active and converts substrate; antibody-bound conjugate is inhibited. Signal (absorbance) is directly proportional to drug concentration in the sample.
- Mechanism
- Sample drug competes with enzyme-labelled conjugate
- Signal
- Absorbance proportional to drug concentration
- Category
- Homogeneous competitive immunoassay
Common questions
Why is EMIT called a homogeneous assay?+
Bound and free enzyme-conjugate fractions do not need to be physically separated before the measurement is taken, unlike heterogeneous immunoassays such as ELISA that require a wash step.
What is the key limitation for forensic interpretation?+
It is a screening test only. Cross-reactivity with structurally related compounds means a positive result must be confirmed by a specific method such as GC-MS or LC-MS before it can support an evidential conclusion.
Related terms
- CEDIA (Cloned Enzyme Donor Immunoassay)
- A homogeneous immunoassay using two inactive fragments of beta-galactosidase, an enzyme donor (ED) fragment conjugated to drug, and an enzyme acceptor (EA)...
- Cross-Reactivity
- The capacity of an antibody raised against one analyte to bind structurally related compounds. In RIA, cross-reactivity is the main driver of...
- Cut-Off Concentration
- The threshold analyte concentration, set by regulatory guidance, above which a specimen is reported as a screen-positive. Choosing the cut-off balances sensitivity...
- Lateral-Flow Immunoassay
- A point-of-care competitive immunochromatographic format on a nitrocellulose strip. In the absence of drug, colloidal gold-labelled antibody is captured at a test...
- Post-Mortem Redistribution
- The movement of drugs from solid tissues into central blood after death, due to diffusion along concentration gradients, autolytic enzyme release, and...