Phoenix Sepsis Score Outperforms pSOFA in Predicting Mortality in Critically Ill Children

Sepsis remains one of the most feared conditions in pediatric intensive care, a syndrome in which the body’s response to infection spirals into organ dysfunction and, all too often, death. For decades, clinicians have relied on scoring systems to identify which children are most at risk, but the tools themselves have been repeatedly revised, debated, and re-validated. Now, a large multicenter study from China has delivered one of the most detailed head-to-head comparisons to date of the two leading contenders: the Phoenix sepsis score, introduced in the 2024 international consensus criteria for pediatric sepsis, and the pediatric sequential organ failure assessment score, known as pSOFA, which has served as the workhorse of pediatric sepsis research since its adaptation in 2017. The verdict, published in the World Journal of Pediatrics, is nuanced: the Phoenix score edges out pSOFA overall, but the advantage dissolves in newborns and weakens considerably in children with blood disorders.

The research team, led by investigators at Children’s Hospital, Zhejiang University School of Medicine, together with collaborators spanning thirteen pediatric intensive care units across China, assembled a retrospective cohort of 2,374 children under eighteen years of age who were admitted to intensive care with suspected infections between 2023 and 2025. Rather than treating this population as a single undifferentiated group, the investigators prespecified two clinically distinct sub-cohorts for focused analysis: a neonatal group of 576 infants aged twenty-eight days or younger, and a hematology group of 494 children, a population in which underlying malignancies, immunosuppression, and hematologic abnormalities complicate both the diagnosis of sepsis and the interpretation of laboratory-based severity scores. This design choice reflects a growing recognition in the field that a scoring system validated in a general pediatric intensive care population may not transfer cleanly to the extremes of age or to immunocompromised patients.

Methodologically, the study followed a disciplined approach to score calculation. For each child, both the Phoenix sepsis score and the pSOFA score were computed using the worst available physiological and laboratory values recorded within the first twenty-four hours of intensive care unit admission. This window matters: early severity assessment is precisely what clinicians need when deciding how aggressively to resuscitate, monitor, and escalate care. The primary outcome was in-hospital mortality, and the principal metric of prognostic accuracy was the adjusted area under the receiver operating characteristic curve, or AUROC, a statistic that captures how well a score discriminates between children who died and those who survived, with 0.5 representing chance-level performance and 1.0 representing perfect discrimination. By adjusting the AUROC, the researchers accounted for confounding structure in the data, strengthening the comparability of the two scores.

The headline finding is statistically clear. Across the full cohort of 2,374 critically ill children, the Phoenix sepsis score achieved an adjusted AUROC of 0.840, significantly outperforming the pSOFA score’s 0.817, with a P value below 0.001. In absolute terms the difference may appear modest, but in the world of mortality prediction models, where incremental gains in discrimination can translate into earlier recognition and redirected resources for the sickest patients, such a difference across a cohort of this size carries weight. The result provides external validation, on a scale and in a healthcare context distinct from the original derivation studies, that the Phoenix framework’s emphasis on four organ systems, respiratory, cardiovascular, coagulation, and neurologic, captures lethal trajectories in infected children at least as well as, and slightly better than, the older pSOFA construct.

The picture grows more complicated in the predefined sub-cohorts. In the hematology group, the Phoenix score again outperformed pSOFA, with adjusted AUROCs of 0.718 versus 0.682, a difference that reached statistical significance at P equal to 0.006. Yet the investigators were careful to characterize discriminative ability in this subgroup as limited for both tools. Children with hematologic disease present a notoriously difficult prediction problem: baseline cytopenias, chemotherapy-related organ toxicity, and altered inflammatory responses can all inflate or deflate organ dysfunction scores independent of sepsis severity. A score of 0.718, while better than chance, leaves substantial room for misclassification, and the authors’ framing suggests that neither score should be treated as a reliable standalone prognostic instrument in this vulnerable population.

In neonates, the story changes again. Among the 576 infants aged twenty-eight days or younger, the Phoenix score posted a strikingly high adjusted AUROC of 0.915 compared with 0.850 for pSOFA, but the difference did not reach statistical significance, with P equal to 0.222. The absence of a significant gap does not mean either score performed poorly; indeed, both achieved excellent discrimination in this low-event-rate setting. Rather, the finding suggests that in newborns the two instruments are statistically interchangeable for mortality prediction, an important practical conclusion given that the Phoenix criteria were designed to span pediatric and neonatal populations and that neonatal sepsis has long posed unique challenges, from nonspecific clinical presentation to the scarcity of neonate-specific validation data for adult-derived scoring frameworks.

Beyond discrimination, the study examined how the scores behave at their operational threshold, the cutoff clinicians actually use to flag sepsis. At the standard threshold of two or more points, both the Phoenix score and pSOFA maintained high sensitivity, exceeding 80 percent across all cohorts, meaning they rarely missed a child who went on to die. The trade-off came in specificity: positive predictive values were low, at or below 50 percent everywhere, and in the neonatal sub-cohort they fell below 8 percent. This asymmetry is not a flaw unique to these scores but a mathematical consequence of applying screening thresholds in settings where deaths are, thankfully, uncommon. A highly sensitive tool catches nearly everyone at risk, but in a population where most children survive, most flagged children will nonetheless survive, producing many false alarms.

The trade-off between sensitivity and positive predictive value took on a different character in the hematology sub-cohort, where the event rate was high enough to make predictive values more meaningful. There, the Phoenix score traded approximately five percentage points of sensitivity for a meaningfully higher positive predictive value than pSOFA. In practical terms, the Phoenix score was somewhat more likely to miss a child who died, but when it flagged a child, that flag was more often correct. Which trade-off a clinician or unit should prefer depends on context: in settings where missing a death is the dominant concern, sensitivity may reign; where flagged patients trigger resource-intensive interventions, a higher positive predictive value reduces unnecessary escalations. The study does not prescribe a choice but equips decision-makers with the quantitative texture needed to make one.

The findings land amid an active international debate about the Phoenix criteria, which were developed and validated by a global consensus effort published in JAMA in 2024 and have since undergone external validation in cohorts from the United States, Bolivia, Australia, and beyond, with mixed results in low-resource settings and emergency departments. The new Chinese multicenter analysis adds a critical piece: evidence from a large, geographically diverse, non-Western cohort, with dedicated attention to neonates and hematology patients, two groups underrepresented in earlier validation work. It also complements the research group’s own prior multicenter study of the Phoenix score, pSOFA, and SIRS criteria in non-intensive care settings, extending the comparison to the sickest children in intensive care.

For the field, the message is one of calibrated confidence. The Phoenix sepsis score can now claim superior discrimination for in-hospital mortality in the general population of critically ill children with suspected infection, supporting its adoption in pediatric intensive care contexts. But the study simultaneously cautions against universal enthusiasm: in neonates, the older pSOFA remains an equally defensible choice, and in children with hematologic disease, both scores fall short of what clinicians would want from a decision-support tool, underscoring the need for population-specific approaches, whether through recalibration, integration of novel biomarkers, or entirely new models tailored to immunocompromised hosts. As sepsis mortality prediction moves from one-size-fits-all scores toward precision risk stratification, this study provides both a benchmark and a reminder that the sickest children often defy the averages on which general scores are built.

Subject of Research: External validation comparing the Phoenix sepsis score and pSOFA for predicting in-hospital mortality in critically ill children with suspected infection.

Article Title: Discrimination performance of the Phoenix sepsis score versus pediatric sequential organ failure assessment for predicting in-hospital mortality in critically ill children: a multicenter external validation study

Article References: Ru, X.-W., Liu, R.-Y., Yang, Z.-H., Huang, C.-Z., Zhang, C., Li, T.-W., Yang, J.-M., Liu, Y., Cui, X.-Y., Chen, H.-B., Zhou, X., Tang, F., Gong, X.-Y., Ling, P., Lv, X., Zeng, Q., Ma, Z., Yuan, B.-Y., Zhu, H., … Ye, Q. (2026). Discrimination performance of the Phoenix sepsis score versus pediatric sequential organ failure assessment for predicting in-hospital mortality in critically ill children: a multicenter external validation study. World Journal of Pediatrics. https://doi.org/10.1007/s12519-026-01073-y

Image Credits: AI Generated

DOI: 10.1007/s12519-026-01073-y

Keywords: Phoenix sepsis score, pSOFA, pediatric sepsis, in-hospital mortality, critical care, neonatal sepsis, hematology, AUROC, external validation, organ dysfunction, predictive scoring, intensive care unit