Blood metagenomic analysis vs. blood culture

Blood metagenomic analysis and blood culture look for evidence of infection using different methods. They may provide complementary information, but they are not interchangeable. The choice of test and interpretation of its results depend on the clinical context and the scope of each test.

In summary:

• Blood metagenomic analysis looks for genetic material from microorganisms in the sample. The groups it covers and the level of identification depend on the method and the specific assay.
• Blood culture and metagenomic sequencing are based on different principles, so their results and limitations should not be treated as equivalent.
• A positive or negative result needs to be assessed alongside the clinical picture and other tests; on its own, it neither confirms nor rules out an infection.
• Information on antimicrobial resistance, turnaround times and clinical utility should be checked for the specific assay before drawing conclusions.

To find out the scope specified by Xenogene, see the clinical metagenomic blood analysis page. The healthcare team determines whether the test is indicated.

What material can metagenomic testing detect in blood?

Metagenomic analysis of blood looks for sequences of genetic material in the sample that may correspond to microorganisms. Without the assay’s technical specifications, it is not possible to say which types of nucleic acid it processes, which groups it covers or the level of identification for each finding.

To find out whether the assay covers bacteria, viruses or fungi, whether it processes DNA, RNA or both, and the taxonomic level at which it reports results — for example, genus or species — you need to consult the specific technical specifications. These features cannot be inferred from the name of the method.

This information helps clarify what a finding in the report means and what falls outside the test’s scope. You can view the available tests in the Xenogene test catalogue and request details about a specific assay.

How does it differ from blood culture?

Metagenomic analysis of blood looks for genetic sequences from microorganisms present in the sample, while blood culture attempts to detect microorganisms that grow under culture conditions. Although both are used when investigating a possible infection, they generate different signals, so their results are not directly equivalent.

In practice, blood culture reports whether growth is observed under the conditions used. Metagenomic sequencing, by contrast, looks for microbial genetic material within the scope of the assay. Each result therefore answers a different question; one should not be interpreted as an automatic substitute for the other.

The comparison should take into account the specific method, the microorganisms it covers and the laboratory’s interpretation criteria. For more information about the general differences between the two approaches, see this explanation of metagenomics versus culture. The usefulness of each test depends on the clinical situation and the information the healthcare team needs.

How should a positive or negative result be interpreted?

A positive result means the assay has detected a signal consistent with microbial genetic material according to its criteria; a negative result means it has not detected that signal in the sample analysed. Neither result confirms nor rules out an infection on its own: both must be interpreted alongside the clinical situation and other available tests.

In practice, the result is interpreted in light of the symptoms, when the sample was collected and the findings of other tests. The healthcare team decides whether it needs to be checked against other findings or whether further testing is needed. The report presents the finding according to the method used, but does not, on its own, establish the cause of the symptoms or replace a professional diagnostic assessment.

To learn about Xenogene’s tool for supporting the interpretation of reports, see Sophia, the clinical AI.

What are the limitations of metagenomic sequencing in blood?

The limitations of metagenomic sequencing in blood depend on the sample type and the validated scope of the assay: it may not detect all microorganisms, and a genetic signal does not automatically identify the cause of an infection or determine treatment.

Before ordering the test, it is worth confirming what genetic material the method analyses, which microorganisms it covers and the level of identification it can provide. This information should be checked in the technical documentation for the specific assay; the features of one test should not be assumed to apply to another.

It is also important to check what information on antimicrobial resistance means, if it is included in the report: detecting genetic material does not, by itself, amount to a treatment recommendation. The healthcare team should interpret the result in the context of the clinical situation and other available tests.

If an urgent infection is being considered, you can consult the information on the test for urgent infections and check the scope stated for that scenario.

When might metagenomic testing in blood be considered?

A healthcare professional may consider metagenomic testing in blood based on the clinical picture, tests already performed and the specific diagnostic question. It is not a universal option. Its suitability also depends on whether the validated scope of the available assay is appropriate for the information being sought.

Before requesting the test, it is useful to clarify the clinical question, what previous results are available and what information the assay covers. If the test’s scope does not address the question, the result may not help guide the next steps.

The decision and interpretation are the responsibility of the healthcare team, which can assess the test alongside the rest of the clinical information. Registered healthcare professionals can consult the access for healthcare professionals to find out how to request testing.

Frequently asked questions

What preparation is needed before the blood draw?

Preparation should follow the instructions given by the healthcare professional and the laboratory handling the blood draw. Do not assume that fasting, stopping medication or making any other changes beforehand is necessary without checking first. If you have questions about collecting, storing or transporting the sample, resolve them before collection.

Does the analysis report antibiotic susceptibility?

It is not possible to say whether the analysis reports antibiotic susceptibility without checking the specific scope of the test and its report. Detecting microbial genetic material and determining which treatments might be effective are different things. The healthcare professional should review what information the test provides and consider other tests where needed.

Can genetic material from microorganisms that are no longer active be detected?

Detecting genetic material alone does not show that the microorganism is active or that it is causing the symptoms. The result should be interpreted alongside the clinical situation and all other available information. Diagnosis is the responsibility of the healthcare professional, who will assess whether further tests are needed.

What does it mean if the metagenomic analysis and blood culture give different results?

Different results do not automatically mean that one of the tests is incorrect. Each method looks for different signals, and interpretation depends on the specific result, the sample and the clinical context. The healthcare team should review the reports together and decide whether further tests are needed to clarify the situation.

Learn about the scope of Xenogene’s clinical metagenomic analysis in blood