What are the differences between ELISA and RIA (radioimmunoassay)?

Basis of differentiation 

ELISA

RIA

Definition 

An immunoassay that uses enzymes to detect antigen-antibody complex

An immunoassay that uses radioisotopes to detect antigen-antibody complex

Principle

Based on the specific binding of an antibody or antigen to an immobilized counterpart on a solid surface 

Based on the competitive binding between unlabeled antibodies or antigens and radioactive-labeled tracers

Labeling molecule

Antibody is labeled with enzymes

Antigen is labeled with radioisotopes 

Sample preparation 

Simpler and more straightforward

Laborious and time consuming

Assay time

Relatively faster, with results within a few hours

Can take longer due to sample preparation time and radioactivity measurement

Sensitivity 

Lower sensitivity 

Higher sensitivity, typically in the picogram-femtogram range

Detection method

Fluorescent or colorimetric signal

Radioactivity measurement

Automation 

Can be easily automated with commercial kits widely available 

Use of radioactive materials limits the extent of full automation 

Antibody cross-reactivity

Less prominent cross-reactivity 

Higher potential for cross-reactivity issues

Special protocol 

No special arrangements required

Radioactive materials require special arrangements for storage, requisition, and disposal

Cost 

Cost-effective overall, especially with commercial kits

More expensive as it requires radioactive reagents and specialized equipment 

Applications 

Widely used in research, diagnostics, and more

Used in limited applications such as specific hormone assays

Radiation hazard reporting 

Radiation hazards do not apply 

Radiation hazards must be documented and reported