Immunexpress SeptiCyte RAPID: Pediatric Sepsis Validation Study Spotlight

Immunexpress announced on October 15, 2026 the publication of a multicenter study showing that its SeptiCyte RAPID blood test can help distinguish sepsis from noninfectious inflammation in critically ill children suspected of sepsis. The study covered 284 children at leading pediatric centers in the United States and Australia, and found an area under the curve (AUC) of 0.83 on its own and 0.87 when combined with routine laboratory results.

What the Study Found

The retrospective, noninterventional study pooled data from four separate studies at pediatric centers in the US and Australia, enrolling children from one month to 18 years of age. Researchers evaluated whether SeptiCyte RAPID's SeptiScore, a 0-15 output generated from a small blood sample, could separate true sepsis from systemic inflammatory response syndrome (SIRS) that has no infectious cause.

Among children with a consensus clinical diagnosis, the test produced an AUC of 0.83, outperforming other clinical parameters used alone or in combination. Adding six routine laboratory tests, including organ dysfunction variables, lifted that figure to 0.87.

Performance held steady across infants and toddlers, children and adolescents, and no statistically significant difference was observed between the US and Australian cohorts. Among clinically adjudicated sepsis patients with positive blood cultures, 68.4% had a Band 4 result, the highest sepsis-probability category the test reports.

"Distinguishing infection-driven sepsis from noninfectious inflammation remains one of the most difficult and time-sensitive decisions in pediatric critical care. The findings in this study demonstrate the promise of a rapid host-response laboratory test to help clinicians manage diagnostic uncertainty in real time during high stakes evolution of a dynamic clinical picture—supporting early sepsis management when sepsis probability is high and consideration of alternative diagnoses and antibiotic stewardship when sepsis probability is low."

— Dr Jerry Zimmerman, lead author and Emeritus Professor, Pediatric Critical Care Medicine, Seattle Children's Hospital, University of Washington

Reading the Score

The study's likelihood-ratio findings describe how the test behaves at either end of its scale. Higher SeptiScores corresponded to a progressively greater probability of sepsis, with a positive likelihood ratio of 3.51, while lower scores carried a likelihood ratio of 0.09, which the company says can enable sepsis to be ruled out. For clinicians managing a child with an uncertain diagnosis, that points toward earlier treatment when the score is high, or toward antibiotic stewardship and alternative diagnoses when it is low.

SeptiCyte RAPID is a sample-to-answer, cartridge-based molecular test that runs on the Biocartis Idylla platform. It needs as little as 250 microliters of whole EDTA blood and returns a SeptiScore in approximately one hour, reported across four interpretation bands reflecting increasing likelihood of sepsis.

The study authors concluded that the test may be used with available clinical and laboratory parameters, including measures of early organ dysfunction, to support earlier and more accurate identification of sepsis in children. The test is intended for use in conjunction with clinical assessments, vital signs and other laboratory findings, not as a standalone answer.

Filling a Pediatric Evidence Gap

The release notes that a number of host response-based sepsis biomarkers have recently become commercially available, but validation studies in children are lacking. The company says this study's results show performance similar to that previously reported for adults. The clinical stakes are high: according to a 2024 Lancet Child & Adolescent Health review, half of the roughly 50 million people affected by sepsis globally each year are neonates and children younger than 19.

Distinguishing sepsis from SIRS in children is difficult because both can present with similar signs, leaving clinicians to rely on judgment and laboratory tests that take time to return. A host-response test measures how a patient's own immune system is reacting, and the company says SeptiCyte RAPID does this in about an hour from a small blood sample, which is a practical advantage when treatment decisions are made before culture results are available.

Company and Regulatory Standing

Immunexpress is a molecular diagnostics company based in Brisbane, Australia, and Seattle, USA, dedicated to improving outcomes for patients with suspected sepsis. Its SeptiCyte technology assesses a patient's dysregulated immune response by quantifying gene expression from whole blood. SeptiCyte RAPID is CE Marked in Europe and has received FDA clearance in the United States for use in hospitalized adult patients suspected of sepsis. In Australia, the Therapeutic Goods Administration has approved it for adult and pediatric application.

The company says its aim is to enable earlier and more confident clinical decision-making during the critical early hours of sepsis evaluation, while helping reduce the economic burden of sepsis on healthcare systems worldwide. The new study, published in Pediatric Critical Care Medicine, adds pediatric-specific evidence for a test whose US clearance currently covers hospitalized adults.