What are well type and membrane type Enzyme Immunoassay (EIA) tests?

Well-Type and Membrane-Type Enzyme Immunoassay (EIA)

Fundamental Structural Differences

Well-type EIAs display results as a color change that can be detected visually or photospectrometrically in microplate wells, while membrane-type EIAs produce results that are visually read from a membrane surface. 1

Well-Type EIA Characteristics

• Results are measured using spectrophotometry that provides a numerical readout based on color intensity in microplate wells 1
• The enzyme converts a colorless substrate into a colored product, with intensity measured by a spectrophotometer 1
• Designed for batch testing of multiple samples simultaneously, making them efficient for high-volume laboratory settings 1
• Total processing time is typically 3-4 hours 1
• Specimens can be stored and transported at ambient temperature 1

Membrane-Type EIA Characteristics

• Results are read qualitatively and visually directly from a membrane without requiring specialized equipment 1
• Packaged as single-use units suitable for testing individual samples rather than batches 1
• Rapid turnaround time of approximately 30 minutes for some formats 1
• Do not require expensive or sophisticated equipment for result interpretation 1
• Specimen material is applied to the membrane where antigen-antibody complexes are trapped and detected 2

Clinical Performance Comparison for Clostridioides difficile Testing

Well-Type EIA Performance

• Well-type EIAs detecting toxins A and B demonstrate mean sensitivity of 82% (95% CI: 0.79-0.84) and specificity of 97% (95% CI: 0.97-0.98) when compared to cytotoxicity assay 1, 3
• Examples include Premier tox A/B (sensitivity 92%, specificity 96%) and ProSpecT A/B (sensitivity 91%, specificity 97%) 1
• Well-type GDH assays show sensitivity of 93% (95% CI: 0.88-0.97) and specificity of 89% (95% CI: 0.87-0.91) 1

Membrane-Type EIA Performance

• Membrane-type EIAs detecting toxins A and B show lower mean sensitivity of 72% (95% CI: 0.69-0.74) but maintain high specificity of 98% (95% CI: 0.97-0.98) 1, 3
• Examples include Immunocard tox A/B (sensitivity 94%, specificity 98%) and Triage tox A (sensitivity 65%, specificity 99%) 1
• Membrane-type GDH assays demonstrate sensitivity of 90% (95% CI: 0.87-0.92) and specificity of 90% (95% CI: 0.88-0.90) 1

Practical Laboratory Applications

When to Use Well-Type EIAs

• Choose well-type formats when processing samples in batches to maximize efficiency and throughput 1
• Appropriate for centralized laboratories with high daily specimen volumes 1
• Requires spectrophotometric equipment and trained laboratory personnel 1

When to Use Membrane-Type EIAs

• Select membrane-type formats for testing solitary samples or in point-of-care settings 1
• Ideal for smaller laboratories, emergency departments, or situations requiring rapid individual results 1
• No specialized equipment required beyond basic laboratory supplies 1

Critical Limitations Regardless of Format

• Neither well-type nor membrane-type toxin EIAs should be used as standalone tests due to suboptimal sensitivity (48-96% depending on specific assay) 3, 4
• At endemic CDI prevalence of 5-10%, positive predictive values range from only 28-77% for most assays 1, 3
• Both formats require integration into a two-step diagnostic algorithm starting with GDH or NAAT screening followed by toxin confirmation 3, 4, 5