Newborn Blood Test Differentiates Bacterial and Viral Infections

Biomarker Ratio Separates Infection Types in Newborns

A blood test measuring two immune cell surface markers distinguished bacterial infections from viral illnesses in infants under three months of age with high accuracy. Researchers presented the preliminary findings at the European Emergency Medicine Congress organized by the European Society for Emergency Medicine (EUSEM). The diagnostic method evaluates the relative expression of CD64 on neutrophils and CD169 on monocytes using flow cytometry.

A fever in an infant younger than three months is a medical emergency because an immature immune system permits infections to progress rapidly. Emergency clinicians must separate serious bacterial infections requiring antibiotics from self-limiting viral illnesses that resolve with monitoring. Standard biomarkers often yield false positives, which drives overtreatment through unnecessary lumbar punctures, hospital admissions, and infant antibiotic regimens.

Test Mechanism and Initial Cohort Findings

The observational investigation enrolled 60 babies evaluated for fever or noninfectious conditions at IRCCS Istituto Giannina Gaslini in Genoa, Italy. Dr. Tommaso Bellini and his research team collected blood samples to track cellular responses via flow cytometry. Neutrophil CD64 levels rise during bacterial infections, while monocyte CD169 levels elevate in response to viral exposure.

Investigators calculated a mathematical ratio comparing CD64 to CD169 for each infant. Babies confirmed to have a bacterial infection averaged a ratio score of 16.22. In contrast, infants with confirmed viral infections averaged a ratio of 0.33, and infants evaluated for noninfectious conditions averaged a ratio of 1.10.

The test identified every bacterial infection in the cohort, recording a sensitivity of 100 percent. The test also achieved a specificity of 96.6 percent, reflecting a very low rate of false-positive bacterial classifications.

Clinical Implications for Pediatric Emergency Care

Differentiating pathogen classes in early life prevents both diagnostic delays and unnecessary medical interventions. Dr. Maša Sorić, head of the emergency department at University Hospital Merkur in Zagreb, Croatia, noted that emergency staff must treat every infant fever as potentially serious until clinical evidence proves otherwise.

Standard biomarkers frequently fail to clearly separate bacterial from viral illnesses in neonates. If validated, a dual-marker ratio test could reduce diagnostic dilemmas in acute care settings. Sparing infants from unwarranted spinal taps and broad-spectrum antibiotics reduces procedural stress and protects the early neonatal microbiome.

Current Limitations and the DISCERN Trial

The diagnostic method currently requires flow cytometry, which limits its practical use to specialist facilities with specialized hardware and trained technicians. Dr. Bellini emphasized that the protocol is not yet a point of care bedside test. Developing a faster, low-cost bedside format remains the primary engineering objective for the research group.

The initial study cohort was limited to 60 infants, with ongoing data collection expected to reach 75 patients. To validate the findings across broader populations, the researchers launched the DISCERN (Discriminating Infection via Surface CD-marker Expression Ratios iN infancy) study. This prospective multicenter trial plans to evaluate the diagnostic accuracy of the ratio in 300 to 500 infants.