Homogeneous vs Heterogeneous
Definition
Homogeneous assays (EMIT, FPIA) need no wash step, so they run fast on clinical analysers. Heterogeneous assays (ELISA, RIA) require a wash to separate bound from free label and are more sensitive.
- Homogeneous examples
- EMIT, FPIA
- Heterogeneous examples
- ELISA, RIA
- Wash step
- Absent in homogeneous, required in heterogeneous
- Sensitivity
- Heterogeneous assays generally more sensitive
Common questions
Why does the wash step affect assay speed and sensitivity so much?+
The wash step in heterogeneous assays physically separates bound label from free label, reducing background signal and improving sensitivity, but it adds time and handling steps that homogeneous assays skip by design.
Why do clinical and forensic toxicology screens typically use homogeneous assays first?+
Homogeneous assays like EMIT run quickly on automated analysers without manual wash steps, making them well suited to high-throughput presumptive screening, with confirmatory testing by more sensitive or specific methods following a positive result.
Related terms
- Antibody
- An immunoglobulin (typically IgG) raised to bind a specific antigen. Source decides specificity: polyclonal antibodies recognise many epitopes, monoclonal antibodies recognise one.
- Antigen
- A molecule recognised by the adaptive immune system through specific binding to an antibody or T-cell receptor. Defined by immunogenicity (capacity to...
- Competitive vs Non-Competitive Format
- Competitive: labelled antigen and sample antigen compete for a limited number of antibody sites; signal is inversely proportional to analyte. Non-competitive (sandwich):...
- ELISA
- Enzyme-Linked Immunosorbent Assay. Heterogeneous, plate-based, enzyme label (HRP, alkaline phosphatase), colour or chemiluminescent readout. Four standard formats: direct, indirect, sandwich, competitive.
- Epitope and Hapten
- Epitope is the small surface patch on an antigen the antibody actually binds. A hapten is a small molecule (most drugs of...
- Label
- The reporter coupled to either the antigen or the antibody so the binding event becomes measurable. Three families dominate: radioisotopes (RIA), enzymes...
- 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...
- RIA
- Radioimmunoassay. Berson and Yalow, 1959. Heterogeneous, competitive, radioisotope label (most often 125-I). Highest sensitivity historically, now displaced in most Indian labs by...