Companion diagnostic testing is a specialized medical testing approach used to identify biological characteristics that help determine whether a particular patient may benefit from a specific medical treatment. These tests examine biomarkers such as genetic mutations, proteins, and other molecular indicators to provide information about treatment suitability, potential safety concerns, or expected therapeutic response.
Companion diagnostics are closely connected to the development of precision medicine, which focuses on understanding differences between patients and their diseases. Traditionally, many treatments were selected primarily according to disease type and clinical characteristics. Advances in molecular biology, genetic sequencing, and laboratory technologies have made it possible to examine individual biological markers more precisely.
Today, companion diagnostic testing is particularly important in oncology, where molecular tests can identify specific tumor characteristics associated with targeted therapies. These tests are also being developed and studied across other therapeutic areas, including immunology and inherited or acquired disease conditions.
Why Companion Diagnostic Testing Matters in Modern Healthcare
Companion diagnostic testing supports treatment decisions by providing information about the biological characteristics of a disease. Different patients with the same general diagnosis may have different molecular profiles, which can influence their response to particular medicines.
These tests help healthcare professionals identify patients who may be suitable for specific treatments or who may face an increased risk of certain adverse reactions.
Major applications include:
Cancer Treatment Selection: Identifying tumor biomarkers associated with particular targeted cancer therapies.
Genetic Mutation Detection: Detecting molecular changes that may influence treatment decisions.
Treatment Safety Assessment: Identifying biomarkers associated with increased risks of serious treatment-related reactions.
Immunotherapy Applications: Examining selected biomarkers that may help assess suitability for certain immunotherapies.
Precision Medicine Research: Supporting the development of treatments based on individual molecular characteristics.
Clinical Research: Helping researchers identify suitable patient groups for clinical trials.
Companion diagnostics are not intended to replace clinical evaluation. Their results are interpreted alongside medical history, disease characteristics, and other relevant clinical information.
Major Types of Companion Diagnostic Testing
Companion diagnostic tests use different laboratory technologies depending on the biomarker being investigated and the associated therapeutic product.
Molecular Diagnostic Testing
Molecular diagnostic testing examines DNA or RNA to identify genetic changes associated with specific diseases or treatment responses.
Common technologies include polymerase chain reaction (PCR), real-time PCR, and next-generation sequencing (NGS).
These methods are used to detect selected genetic mutations, gene rearrangements, and other molecular characteristics.
Immunohistochemistry Testing
Immunohistochemistry (IHC) uses antibodies to identify specific proteins in tissue samples. It is widely used in cancer diagnostics to examine protein expression and classify tumor characteristics.
The testing process generally involves preparing tissue sections, applying antibodies, detecting binding reactions, and evaluating staining patterns under a microscope.
Fluorescence In Situ Hybridization
Fluorescence In Situ Hybridization (FISH) is a laboratory technique that uses fluorescent probes to identify specific DNA sequences within cells.
It can help detect gene amplification, rearrangements, and chromosomal abnormalities. FISH is used in selected cancer-related diagnostic applications.
Next-Generation Sequencing
Next-generation sequencing analyzes multiple DNA or RNA regions simultaneously. It allows laboratories to examine several genetic alterations within a single testing workflow.
NGS platforms are increasingly relevant to comprehensive genomic profiling and biomarker-based research.
Protein and Biomarker Detection Assays
Some companion diagnostic approaches examine proteins and other biological substances using immunoassays, antibody-based detection, or specialized laboratory platforms.
These methods support the identification and measurement of selected biomarkers associated with disease characteristics or treatment response.
Companion Diagnostic Manufacturing Processes and Technologies
Manufacturing companion diagnostic products involves several stages, including assay development, reagent preparation, instrument integration, analytical validation, and quality control.
The production process depends on whether the diagnostic product is a molecular test kit, immunohistochemistry assay, sequencing-based platform, or another type of in vitro diagnostic device.
Biomarker and Assay Development
The development process begins with identifying a biomarker associated with a specific therapeutic product.
Researchers investigate the relationship between the biomarker, disease characteristics, and potential treatment response. They then develop an assay designed to detect the relevant biological signal.
Reagent and Diagnostic Kit Manufacturing
Diagnostic kit manufacturing involves preparing and assembling the materials required for laboratory testing.
These may include:
PCR primers and probes.
Antibodies and detection reagents.
Enzymes and buffers.
Nucleic acid extraction reagents.
Calibration and control materials.
Sample preparation components.
Manufacturers establish controlled production procedures to maintain reagent consistency and product performance.
Instrument and Software Integration
Modern molecular diagnostic platforms combine laboratory instruments, testing reagents, and software systems.
Automated analyzers may manage sample processing, amplification, signal detection, and result generation. Software supports data analysis, quality checks, and interpretation according to the assay's validated specifications.
Analytical and Clinical Performance Evaluation
Before a diagnostic product is used for its intended clinical purpose, its performance must be evaluated.
Important assessment areas include analytical sensitivity, specificity, accuracy, reproducibility, and clinical performance.
These evaluations help determine whether the test can reliably detect the intended biomarker in relevant patient samples.
Global Companion Diagnostic Manufacturers and Suppliers
The companion diagnostics industry includes pharmaceutical companies, biotechnology organizations, molecular diagnostic manufacturers, laboratory equipment developers, and specialized reagent suppliers.
Some internationally recognized companies involved in diagnostic technologies include:
Roche Diagnostics: Develops molecular diagnostic systems, tissue-based testing technologies, and laboratory diagnostic products.
Abbott: Operates in molecular diagnostics, immunoassay testing, and laboratory diagnostic systems.
Thermo Fisher Scientific: Develops molecular biology reagents, genetic analysis technologies, and laboratory instruments.
Agilent Technologies: Develops pathology, genomics, and laboratory testing technologies.
Illumina: Develops DNA sequencing platforms and genomic analysis technologies.
QIAGEN: Develops sample preparation, molecular testing, and genomic analysis technologies.
bioMérieux: Develops diagnostic systems and laboratory testing solutions.
These companies operate across different areas of the diagnostics industry. Not every product manufactured by these organizations is an authorized companion diagnostic. Regulatory authorization and therapeutic associations depend on individual tests and their intended uses.
Companion Diagnostic Applications in Precision Medicine
Precision medicine uses biological, genetic, and clinical information to support treatment decisions. Companion diagnostics provide an important connection between laboratory testing and targeted therapeutic products.
Oncology and Targeted Cancer Therapy
Oncology is one of the most established applications of companion diagnostic testing.
Cancer cells can contain specific genetic alterations or protein expression patterns that influence treatment selection. Molecular diagnostic platforms help identify these characteristics in tumor tissue or other appropriate biological samples.
For example, testing for selected EGFR mutations can help identify patients with certain types of lung cancer who may be eligible for corresponding targeted therapies.
Immunotherapy and Biomarker Detection
Certain cancer immunotherapies are associated with biomarkers such as PD-L1 expression or other molecular characteristics.
Immunohistochemistry and molecular diagnostic technologies can help identify relevant biomarkers when a corresponding treatment has an established testing requirement.
Genetic and Molecular Profiling
Genomic profiling examines multiple genetic characteristics within a biological sample. It can identify molecular alterations that may be relevant to treatment selection or clinical research.
NGS platforms are particularly useful when several biomarkers need to be examined within a single testing workflow.
Personalized Treatment Research
Companion diagnostic technologies are also being investigated in areas beyond oncology. Research involving immunological markers, genetic variations, and molecular signatures may contribute to the development of additional biomarker-based treatment approaches.
Companion Diagnostic Testing Industry Developments, 2024–2026
The companion diagnostics industry continues to evolve through improvements in molecular biology, laboratory automation, genomic analysis, and regulatory frameworks.
Important developments include:
Advanced Genomic Profiling: NGS technologies are supporting broader molecular analysis by examining multiple genetic alterations in a single workflow.
Artificial Intelligence in Diagnostics: AI-based software is being explored for pathology image analysis, biomarker interpretation, and laboratory data processing. Clinical validation remains important before such systems are used for specific diagnostic purposes.
Multiplex Biomarker Testing: Diagnostic platforms increasingly support the examination of multiple biomarkers within a single testing procedure, depending on assay design and validation.
Drug and Diagnostic Co-Development: Pharmaceutical and diagnostic companies increasingly coordinate therapeutic development with biomarker testing strategies. This helps establish how a corresponding diagnostic test will support the intended treatment.
Regulatory Framework Development: Regulatory agencies continue to provide guidance on analytical performance, clinical evidence, and companion diagnostic authorization. The European Medicines Agency updated its procedural guidance in December 2024, with further FAQ updates during 2025 and 2026.
Digital Pathology: Digital imaging and computational analysis are expanding the tools available for examining tissue samples and evaluating selected biomarkers.
Companion Diagnostic Regulations and Government Oversight
Companion diagnostic products are regulated as medical devices or in vitro diagnostic devices according to their intended use and applicable national legislation.
In the United States, the Food and Drug Administration (FDA) regulates companion diagnostic devices. The FDA evaluates relevant analytical and clinical evidence and maintains a list of authorized companion diagnostic devices. Certain companion diagnostics require premarket approval, depending on their regulatory classification and intended use.
In the European Union, companion diagnostics fall under the In Vitro Diagnostic Medical Devices Regulation (IVDR 2017/746). The framework includes risk-based classification, conformity assessment, and scientific consultation involving the European Medicines Agency in applicable cases.
In India, the Central Drugs Standard Control Organisation (CDSCO) regulates in vitro diagnostic medical devices under the Medical Devices Rules, 2017. IVD products are classified into four risk categories:
Class A: Low-risk diagnostic devices.
Class B: Low-moderate-risk diagnostic devices.
Class C: Moderate-high-risk diagnostic devices.
Class D: High-risk diagnostic devices.
Applicable requirements include manufacturing and import licensing, performance evaluation, quality management, and regulatory documentation.
Other important regulatory considerations include:
Analytical and clinical performance validation.
Manufacturing quality management systems.
Reagent stability and storage conditions.
Laboratory testing procedures.
Patient data privacy and information security.
Post-market monitoring and adverse event reporting.
Companion Diagnostic Testing Tools and Technical Resources
Several scientific platforms and technical resources support biomarker research, assay development, and molecular diagnostic testing.
Examples include:
Thermo Fisher Ion Torrent: A sequencing technology platform used in selected genomic research and diagnostic workflows.
Illumina Sequencing Systems: Platforms used for DNA sequencing and genomic analysis.
QIAGEN QIAstat-Dx: A molecular diagnostic platform for selected multiplex testing applications.
Roche cobas Systems: Laboratory platforms used for molecular and other diagnostic testing.
Agilent Pathology Technologies: Instruments and technologies used in tissue-based diagnostic workflows.
NCBI: A scientific resource for genomic sequences, molecular information, and biological research.
ClinVar: A database containing information about relationships between genetic variations and human health.
The intended applications and regulatory status of individual platforms and assays must be evaluated separately.
Frequently Asked Questions About Companion Diagnostic Testing
1. What is companion diagnostic testing used for?
Companion diagnostic testing identifies biomarkers that help determine whether a patient may benefit from a particular therapeutic product or may face an increased risk of certain treatment-related side effects.
2. What technologies are used in companion diagnostic testing?
Common technologies include PCR, real-time PCR, next-generation sequencing, immunohistochemistry, fluorescence in situ hybridization, and immunoassays.
3. Who are the major companion diagnostic manufacturers?
Major companies involved in relevant diagnostic technologies include Roche Diagnostics, Abbott, Thermo Fisher Scientific, Agilent Technologies, Illumina, QIAGEN, and bioMérieux.
4. What is the difference between molecular diagnostics and companion diagnostics?
Molecular diagnostics is a broad category of testing that examines DNA, RNA, and other molecular characteristics. Companion diagnostics are tests specifically associated with a therapeutic product to support its safe and effective use.
5. How does companion diagnostic testing support precision medicine?
It identifies relevant biological markers that help healthcare professionals understand disease characteristics and evaluate whether a patient may be suitable for a specific biomarker-associated treatment.
Conclusion
Companion diagnostic testing connects molecular diagnostics, biomarker detection, and modern therapeutic development. Technologies such as PCR, NGS, immunohistochemistry, and FISH support the identification of biological characteristics associated with specific treatments. Diagnostic manufacturers continue to develop advanced testing platforms, reagents, and laboratory technologies for precision medicine applications. Regulatory oversight, clinical validation, and manufacturing quality standards remain essential to the development and use of companion diagnostic products.