- cheapest and simplest technique
- an analytical method used in Clinical Toxicology
- commonly used in screening blood (serum) for TDM (Therapeutic Drug Monitoring) and as a primary screening procedure of abused drugs and their metabolines in the urine.
- it is the first homogenous assay to be widely used.
- the separation using antibody specificity (antigen binding).
- measurement of enzyme-substrate reactions using visible spectroscopy, and standard curve.
- produces reliable results
- the test utilizes antibodies that are enzyme linked and react only with the specific substance in the sample(urine or blood) is positive with the particular drug being tested.
Components of the Assay & Principle:
- drug in the specimen (urine/serum)
- Ab -- Antibody
- Ag -- Antigen
- enzyme labeled antigen
- enzyme bound to drug
- reagent enzyme Ag
- Ag being measured competes for the Ab binding sites with the antigen that has been labeled with an enzyme ---->the antibody reagent blocks any enzymatic activity when it is bound with the reagent enzyme Ag complex (thus preventing the formation of the product with a substrate) ----> then the free Ag-enzyme complexes compete with the Ag (in the sample) ----> forming a color change which are proportional to the concentration of the Ag present in the tested sample.
References: Clinical Laboratory Diagnosis by Henry et. al.