Sepsis: 5 ways early pathogen identification can change care

In sepsis, identifying the pathogen early can help guide the review of antimicrobial treatment, the search for the source of infection and any additional testing. It does not replace clinical assessment, cultures, antimicrobial susceptibility testing or source control.

In summary:

• Identifying the microorganism involved may help the healthcare team assess whether the initial antimicrobial treatment should be adjusted.
• Detecting genes associated with antimicrobial resistance does not, on its own, demonstrate phenotypic resistance or automatically determine treatment.
• Metagenomic sequencing in blood can complement, but does not necessarily replace, culture, antimicrobial susceptibility testing and clinical assessment.
• AMC Critical for urgent blood infections has a stated turnaround time of 24 to 72 hours from receipt of the sample, depending on the service contracted (Xenogene, September 2026).

The result should be interpreted alongside the patient’s clinical history, progress and all other available test results.

What changes in sepsis when the pathogen is identified early?

Early identification of the pathogen can provide a microbiological basis for the healthcare team to reassess antimicrobial treatment, look for the source of the infection and consider additional tests. However, sepsis is recognised and treated by integrating clinical signs, laboratory results, imaging and microbiology; no single result determines management on its own.

Detecting genetic material from a microorganism does not, by itself, establish a clinical diagnosis of sepsis. The result must be considered alongside the patient’s medical history, examination, clinical course and other tests.

This information can help guide three decisions:

• Review whether antimicrobial coverage remains appropriate.
• Investigate the possible source of infection.
• Consider cultures, imaging or other complementary tests.

Treatment decisions are made by the healthcare team and also depend on the severity of the condition, the patient’s medical history and their response to treatment. To learn about the available options for infections and other indications, see the catalogue of available tests.

What information does antimicrobial resistance provide?

Information on antimicrobial resistance can help assess whether the microorganism detected has markers compatible with reduced susceptibility to certain drugs. However, it must be interpreted alongside the sample, the analytical signal, the antibiogram when available, and the clinical situation: a molecular marker does not, on its own, predict the full response.

Antimicrobial resistance is the ability of a microorganism not to respond adequately to an antimicrobial. A molecular analysis can identify genes or markers associated with that resistance, while phenotypic susceptibility measures how the microorganism responds under laboratory conditions.

This information may help review antimicrobial coverage, always under medical supervision. The microorganism, the sample, and the patient’s clinical course must also be taken into account when interpreting the result. Metagenomic analysis in blood may provide complementary information, but it does not replace the antibiogram or determine treatment on its own.

Can metagenomic sequencing replace blood culture?

Metagenomic sequencing does not universally replace blood culture: it can detect genetic material from microorganisms and certain markers, while culture attempts to recover a viable organism and allows its susceptibility to be assessed through antimicrobial susceptibility testing when it grows under suitable conditions.

Each technique addresses a different question:

• Culture: can a recoverable microorganism be grown from the sample?
• Antimicrobial susceptibility testing: how does that isolated microorganism respond to specific antimicrobials?
• Metagenomic sequencing: is genetic material compatible with microorganisms or markers detected in the sample?

Their turnaround times, analytical limitations and interpretive possibilities are not equivalent. For this reason, a metagenomic result can complement conventional microbiology, but it should be assessed alongside culture, antimicrobial susceptibility testing when available and the clinical situation. For a broader comparison, see this analysis of metagenomic sequencing and culture.

How is a positive result interpreted when sepsis is suspected?

A positive result when sepsis is suspected is interpreted alongside the clinical history, physical examination, clinical course, probable site of infection, cultures and previous treatments. It also takes into account which microorganism was detected and the analytical signal. On its own, it does not demonstrate an invasive infection or that the microorganism is viable.

The layered review includes:

• Microorganism: checking whether it is consistent with the clinical picture and suspected site of infection.
• Contamination or colonisation: assessing whether the detection may not represent an invasive infection.
• Analytical signal: interpreting its intensity and context without automatically treating it as a measure of severity.
• Previous treatments: considering the antimicrobials received before the sample was collected.
• Clinical course: comparing the result with the clinical response and culture results.

The report can help guide further testing and therapeutic review, but the decision rests with the healthcare team. Healthcare professionals can consult Xenogene’s access for professionals.

When can an urgent blood test be available?

At Xenogene, an urgent blood test may be available within 24 to 72 hours of receiving the sample, depending on the service contracted. This timeframe depends on the type of test, the quality and suitability of the sample, and the laboratory workflow; it does not correspond to the time until a clinical decision is made and does not replace urgent care.

AMC Critical is intended for the analysis of severe or urgent infections in blood. An adequate sample must be received before processing can begin, and any preanalytical issue may affect the workflow or require the sample to be reassessed.

When sepsis is suspected, the healthcare team should apply the indicated clinical measures without waiting for a metagenomic report. The result may provide additional information for the assessment, but it must be interpreted alongside the clinical examination, the patient’s progress, cultures, and all other available tests.

Frequently asked questions

What is the difference between sepsis and bacteraemia?

Bacteraemia is the presence of microorganisms in the blood, whereas sepsis is a severe systemic response associated with an infection. They can coexist, but they are not synonymous: bacteraemia can occur without sepsis, and sepsis is not always confirmed by a positive blood culture. The difference must be assessed by the healthcare team in the clinical context.

Does prior antibiotic treatment affect the test result?

Yes. Antibiotics administered before the sample is collected can affect the detection of the microorganism, especially in techniques based on microbial growth. The specific effect depends on the treatment, timing, sample and technique used. For this reason, the report should include this information and be considered alongside the patient’s clinical course and other test results.

What does it mean to detect genetic material without demonstrating that the microorganism is alive?

Detecting genetic material indicates that a signal compatible with a microorganism has been identified, but it does not by itself demonstrate that the microorganism is alive, that it is causing the infection or that it is the source of the clinical condition. Interpretation should consider the sample, analytical signal, suspected site of infection, previous treatments and available microbiological information.

What type of sample is used to investigate a severe bloodstream infection?

To investigate a severe bloodstream infection, the sample must be the one indicated by the clinical pathway and the requested assay. The exact type, volume, container and transport conditions depend on the laboratory procedure. Before sending the sample, the healthcare professional should confirm the requirements for AMC Critical and check which samples the service accepts.

Who should interpret a metagenomic result when sepsis is suspected?

It should be interpreted by a healthcare professional with access to the patient’s medical history and all other test results. The report may provide microbiological information to support the assessment, but it does not by itself determine treatment, the need for further tests or source-control management. When sepsis is suspected, clinical care should not wait for the report.

Request information about AMC Critical for severe bloodstream infections

Sources

• AMC Critical: infecciones urgentes en sangre — xenogene.es