Enzyme IA

These are naturally occurring molecules. It reacts with suitable substrates to produce products

ENZYMES

ENZYMES produces these products

Chromogenic, Fluorogenic, Luminescent

Cheap, readily available and has a long shelf life

Can be used quantitatively or qualitatively

Enzyme labels

Typical enzymes used:

Horseradish peroxidase

G-6PD

Alkaline phosphate

B-D-Galactosidase

Most common enzyme label

Horseradish peroxidase

Has the highest turn-over rate or conversion of substrate

Alkaline Phosphatase

Heterogenous Enzyme Immunoassay

Competitive EIA

Noncompetitive EIA

Capture assay

Competitive EIA is also known as

Competitive Enzyme-Linked Immunosorbent Assay (ELISA)

Enzyme activity is inversely proportional to the concentration of the test substance

COMPETITIVE EIA

NONCOMPETITIVE EIA is Often referred to as

indirect ELISA

Indirect ELISA is one of the most frequently used immunoassays in the clinical

laboratory due to its

sensitivity,

specificity,

simplicity, and

low cost

It measures Ab production to infectious agents that are difficult to isolate and used as an autoantibody testing

NONCOMPETITIVE EIA

NONCOMPETITIVE EIA is Preferred screening test for detecting antibody to

HIV & Hepatitis A and C

Principle: Based on the principle of change in enzyme activity as specific Ag-Ab combination occurs. 

HOMOGENEOUS ENZYME IMMUNOASSAY

Enzyme activity is DIRECTLY proportional to the amount of Ag in the

sample

CAPTURE ASSAYS: IMMUNOLOGICAL SANDWICH

CAPTURE ASSAYS: IMMUNOLOGICAL SANDWICH is often called

Sandwich immunoassays or capture assays

Capture assays are best suited to antigens that have multiple

determinants, such as

antibodies,

polypeptide hormones,

proteins,

tumor markers,

and microorganisms, especially viruses.

Enzyme concentration is directly in proportion to the concentration of

patient antigen or hapten present in the test solution

HOMOGENEOUS ENZYME IMMUNOASSAY

HOMOGENEOUS ENZYME IMMUNOASSAY Chief uses 

Determination of low MW analytes

Hormones and therapeutic drugs

Drugs of abuse in both serum and urine