How to choose biomarkers in clinical testing

There is no universally most important clinical biomarker: its usefulness depends on the clinical question, the sample analysed, the quality of the evidence and the professional interpretation of the result.

In summary:

• A biomarker is a measurable characteristic that can provide information about a biological process, a disease, a response to treatment or the state of an organism.
• The importance of a biomarker depends on the clinical question, the sample, the method and the available evidence—not on whether it appears altered in isolation.
• Biomarkers of inflammation, infection, digestive function, genetic variants and liquid biopsy address different questions and are not equivalent.
• An analytical result can help guide clinical assessment, but it must be considered alongside symptoms, medical history, examination findings and professional judgement.

To organise the available options, it is advisable to define what you want to investigate first and consult the Xenogene test catalogue, without confusing a specific measurement with a diagnosis.

What Is a Biomarker and What Is It Used For in Clinical Testing?

A biomarker is a measurable characteristic of the body that can provide information about a biological process, a disease, a response to treatment, or a person’s health status. However, its usefulness depends on the sample, the analytical method, the supporting evidence, and its interpretation alongside the patient’s data.

Measuring a biological signal does not automatically establish a diagnosis. The result must be considered in relation to symptoms, medical history, physical examination, and other tests. It is also important to understand what question the test is intended to answer: different markers are selected to investigate inflammation, infection, digestive function, or a genetic variant.

For this reason, before interpreting a report, it is worth checking:

• what the test actually measures;
• which sample has been analysed;
• how the result was obtained;
• what limitations it has;
• who should integrate it into the clinical assessment.

To understand the scope of a test, you may find this guide on clinical and consumer testing useful.

How Are the Most Relevant Biomarkers Selected for Each Case?

Selecting the most relevant biomarkers requires starting with the clinical question, choosing an appropriate sample, assessing each test’s ability to detect the process being investigated and distinguish it from other situations, reviewing its limitations, and deciding how the result will be integrated with the clinical history, examination and other tests.

The aim is not to accumulate tests, but to select those that address the question and can be interpreted in the right context. A practical way to structure the decision is:

• Define the clinical question: detection, characterisation, monitoring or support for a decision.
• Select the appropriate sample and timing; both determine what can be measured.
• Assess sensitivity and specificity: the former identifies cases with the process; the latter distinguishes them from people who do not have it.
• Review the method, controls, study population and its limitations.
• Plan how the results will be integrated with other data and, where appropriate, consult the professional access.

Which biomarkers can provide guidance on inflammation, infection, and digestive function?

Inflammatory biomarkers can provide information about inflammatory activity; metagenomic detection can contribute to investigating genetic material from microorganisms in a sample, and digestive function tests provide information about specific processes. However, no isolated result confirms a disease on its own or replaces professional clinical assessment.

The choice depends on the question to be answered:

• Inflammation: may be relevant when it is necessary to assess whether inflammatory activity is present and relate it to symptoms and other findings.
• Infection: metagenomics investigates genetic material from microorganisms; finding it does not, on its own, demonstrate an active infection.
• Digestive function: these tests examine specific processes, such as the activity of certain microbial products or the response to a substance.
• Sample and context: blood, stool, or other samples provide different information and have their own limitations.

In systemic infections, the metagenomic blood analysis may be considered, always as part of professional assessment and alongside the results of other tests.

What Do Genetic Variants and Liquid Biopsy Contribute as Biomarkers?

Genetic variants can be classified to estimate their potential clinical relevance, while liquid biopsy analyses tumour signals present in a sample. Both approaches provide different information about predisposition, detection, or monitoring, but they require validated methods, clinical context, and trained professionals to avoid interpreting an isolated result as a diagnosis.

A genetic variant does not necessarily indicate a disease. Its interpretation takes into account the available evidence, the type of variant, the gene affected, and the person’s personal and family history. Classification can provide guidance on hereditary predisposition, although it should be confirmed and placed in context when it may influence clinical decisions. Genetic variant interpretation should be carried out using recognised criteria and professional review.

Liquid biopsy examines circulating biological material, such as tumour signals in blood. It may be considered to support characterisation, monitoring, or the detection of residual disease in specific contexts, but its usefulness depends on the tumour, the sample, the method, and the clinical question. The absence of a signal does not, on its own, rule out disease.

How Should an Altered Biomarker Be Interpreted Without Overdiagnosing?

An altered biomarker does not, on its own, confirm a disease: its significance may depend on individual variability, a temporary condition, pre-analytical factors, the limitations of the method, and the clinical context. It should therefore be reviewed with a healthcare professional and, where appropriate, assessed alongside other tests.

A result outside the reference range does not necessarily indicate disease. Reference ranges are used to compare a result with a specific population or condition, but they may vary according to the sample, the method, and the person’s characteristics.

False positives may also occur, when a result suggests a problem that is not confirmed, as well as false negatives, when a test fails to detect a process that is present. Interpretation should take into account symptoms, medical history, medication, sample quality, and consistent results from other tests.

To organise the review of a report, Sophia, the clinical AI, may be used without replacing assessment by a healthcare professional or any confirmation required in each case.

Frequently asked questions

Does an altered biomarker mean that a disease is present?

Not necessarily. An altered result may be related to different processes, individual variability, or the conditions of the sample and the analysis. Its significance depends on the clinical context, the applicable reference values, and other findings. On its own, it does not confirm a disease or determine what action should be taken.

Is it better to analyse many biomarkers at the same time?

Not always. Requesting more biomarkers does not guarantee more useful information and may make interpretation more difficult if there is no defined clinical question. The selection should reflect the symptoms, medical history, available sample, and information that needs to be obtained. A healthcare professional can assess which tests are relevant and how to interpret them together.

What is the difference between a biomarker and a reference value?

A biomarker is a characteristic that can be measured in a sample or in the body; a reference value is an interval or criterion used to put the result into context for a particular population and method. Being outside that interval does not automatically mean that a disease is present, because interpretation depends on the clinical and analytical context.

Can a metagenomic analysis replace a conventional clinical test?

Not in general. A metagenomic analysis can provide information about genetic material present in a sample, but detecting that material does not, on its own, demonstrate an active infection or establish its clinical cause. The choice of test depends on the question being investigated and should be integrated with professional assessment and other evidence.

Who should interpret the results of a clinical analysis?

The results should be interpreted by a healthcare professional with the clinical information needed to assess their relevance. This review includes, where appropriate, symptoms, medical history, treatments, sample characteristics, the method used, and other results. A report can guide the assessment, but it does not replace clinical evaluation and should not be used to make decisions in isolation.

Consult Xenogene’s test catalogue and review which tests may be relevant to the clinical question you want to investigate.