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Defining the smallest analyte concentration an immunoassay can measure
E N Brown1, T J McDermott, K J Bloch
1Statistics Research Laboratory, Anesthesia Service, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA. brown@srlb4.mgh.harvard.edu
Clinical Chemistry
|June 1, 1996
Summary
This study unifies minimal detectable concentration (MDC) definitions for immunoassays using Bayes' theorem. A new MDC calculation for prostate-specific antigen (PSA) assays suggests current measurements may overstate their ability to detect early cancer recurrence.
Area of Science:
- Biochemistry
- Analytical Chemistry
- Immunology
Background:
- The minimal detectable concentration (MDC) is a critical parameter for immunoassays, defining the lowest reliably measurable analyte concentration.
- Existing MDC definitions lack a unified mathematical framework, leading to inconsistencies in assay evaluation.
- Accurate MDC determination is crucial for diagnostic accuracy, quality control, and assay development.
Purpose of the Study:
- To develop a unified mathematical definition for the minimal detectable concentration (MDC) of immunoassays using Bayes' theorem.
- To explore the implications of a unified MDC definition on defining positive results, quality control, and assay design.
- To re-evaluate the MDC of a specific immunoassay, the microparticle capture enzyme immunoassay for prostate-specific antigen (PSA), using the unified approach.
Main Methods:
- Application of Bayes' theorem to reconcile and unify five existing mathematical definitions of MDC.
- Development of a novel, unified MDC calculation.
- Illustrative application of the unified MDC definition to a prostate-specific antigen (PSA) immunoassay on the Abbott IMx system.
Main Results:
- A unified definition for immunoassay MDC was established using Bayes' theorem.
- The unified approach revealed that the MDC for the example PSA assay was 4.1-7.1 times higher than previously reported.
- This significant difference suggests a potential overestimation of the current assay's capability in measuring low PSA concentrations.
Conclusions:
- The unified MDC definition provides a robust framework for evaluating immunoassay performance.
- The re-evaluation of the PSA assay indicates that its sensitivity for detecting low PSA concentrations, relevant for early prostate cancer recurrence detection, may be overstated.
- This work has significant implications for immunoassay quality control, diagnostic test interpretation, and the reliable measurement of biological substances at low levels.