S1 Data set -

Introduction
To determine the threshold of umbilical cord blood procalcitonin for early-onset neonatal infection diagnosis.
Method
This prospective study was conducted on 126 neonates in the neonatal care unit of Hue University of Medicine and Pharmacy Hospital, Vietnam, from June 01, 2023 to August 31, 2024. All neonates showed signs at birth or risk factors for early-onset infection (EOI) and were divided into two groups: EOI group and non-EOI group. Umbilical cord blood samples were collected for procalcitonin analysis immediately after birth.
Results
The median procalcitonin (PCT) levels in umbilical cord blood were significantly higher in the EOI group (0.154 ng/ml [0.092–0.197]) compared to the non-EOI group (0.097 ng/ml [0.082–0.134]; p < 0.001). Receiver operating characteristic (ROC) curve determined the optimal threshold value of PCT of 0.142 ng/ml with an AUC 0.751 (95% CI: 0.661–0.841, p<0.001) in the total population. At this cut-off, the Se, Sp, PPV, and NPV were 68.2%, 76.8%, 61.2%, and 81.8%, respectively. The optimal cut-off value for preterm neonates was 0.122 ng/ml (AUC: 0.785, 95% CI: 0.658–0.911, p<0.001) corresponding a Se of 79.2%, Sp of 74.1%, PPV of 73.1%, and NPV of 80.0%. In term group, the optimal cut-off value was 0.150 ng/ml (AUC: 0.726, 95% CI: 0.583–0.860, p<0.01), with a Se of 60.0%, Sp of 80.4%, PPV of 52.2%, and NPV of 84.9%.
Conclusions
Umbilical cord blood PCT concentration were elevated in neonates with EOI. PCT could be a valuable marker for the early diagnosis of EOI.