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Knowledge

Introduction to Molecular Diagnostics

An introduction to molecular diagnostic methods used to detect and characterize nucleic acids and other molecular targets.

5 min read Laboratory Quality Assurance #specimen
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Learning Objectives

By the end of this resource you should be able to:

- Define molecular diagnostics.
- Identify common molecular diagnostic approaches.
- Describe the broad stages of a molecular testing workflow.
- Explain the purpose of controls and contamination prevention.

Introduction to Molecular Diagnostics

Overview

Molecular diagnostics uses laboratory methods to detect, measure, or characterize molecular targets, particularly nucleic acids such as DNA and RNA.

These methods can support detection of infectious agents, inherited variants, acquired genetic changes, and other clinically relevant molecular targets.

Common molecular approaches

Depending on the laboratory, molecular testing may involve:

  • Nucleic-acid extraction
  • Polymerase chain reaction (PCR)
  • Reverse-transcription PCR
  • Real-time or quantitative PCR
  • Isothermal amplification
  • Sequencing
  • Hybridization-based methods
  • Other validated amplification or detection technologies

A simplified molecular workflow

A broad workflow can include:

  1. Specimen collection and identification
  2. Specimen preparation
  3. Nucleic-acid extraction or target preparation
  4. Amplification or another analytical process
  5. Detection
  6. Control assessment
  7. Result interpretation
  8. Reporting

Actual workflows vary substantially by assay.

Controls

Molecular assays commonly use controls designed to provide information about aspects of analytical performance.

Examples may include:

  • Positive controls
  • Negative controls
  • Internal controls
  • Extraction controls

The purpose and acceptance criteria of each control are method-specific.

Contamination prevention

Because amplification can produce large quantities of target material, contamination control is an important part of molecular laboratory practice.

Laboratories may use:

  • Physical workflow separation
  • Dedicated equipment
  • Controlled movement of materials
  • Appropriate personal protective practices
  • Validated decontamination procedures
  • Appropriate negative controls

Specimen and extraction quality

Poor specimen quality or inefficient extraction can affect target recovery. Molecular results should therefore be considered alongside specimen requirements and assay controls.

Result interpretation

A molecular result can mean different things depending on what the assay detects. Detection of nucleic acid does not automatically establish every aspect of clinical disease, viability, infectiousness, or treatment response.

Interpretation depends on the assay target, analytical characteristics, specimen, timing, and clinical context.

Key points

  • Molecular diagnostics detects or characterizes molecular targets.
  • PCR is one important molecular technology but not the only one.
  • Controls are integral to many molecular assays.
  • Contamination prevention is essential.
  • Assay-specific validation and interpretation are required.

References

  • World Health Organization. Molecular diagnostic laboratory resources.
  • NCBI Bookshelf. Molecular biology and laboratory-method resources.
  • ISO 15189:2022. Medical laboratories — Requirements for quality and competence.