IntroductionNeonatal sepsis accounts for 0.97% of all disability-adjusted life years worldwide. Interleukin-6 has been used in sepsis diagnosis, but cut-off values are missing.MethodsNeonates admitted to the neonatal wards with measurements of serum interleukin-6 born between September 2015 and September 2019 were retrospectively analysed. Mean serum interleukin-6 values of patients who never had increased laboratory parameters of infection nor died during their stay and mean interleukin-6 values on the day of blood sampling for a later positive culture in patients with culture-confirmed sepsis were analysed for each time period.ResultsIn all, 8.488 values in 1.695 neonates, including 752 very-preterm-infants and 701 very-low-birthweight infants, were analysed. The AUC for interleukin-6 was 0.84–0.91 in all neonates, 0.88–0.89 in very-preterm and 0.89–0.91 in very-low-birthweight infants. Using interleukin-6 cut-off values of 80 pg/ml on day of life 1, 40 pg/ml on day of life 2–7 and 30 pg/ml after day of life 7, a sensitivity of 75% and a specificity of 81% for culture-confirmed sepsis were achieved. In very-preterm infants, the corresponding values were 74% for sensitivity and 83% for specificity and in very-low-birthweight infants 74% and 86%, respectively.ConclusionSerum interleukin-6 has high accuracy for the detection of neonatal sepsis.ImpactSerum interleukin-6 can be used with high accuracy to detect sepsis in neonates with the cut-off values of 80 pg/ml on day of life 1, 40 pg/ml on day of life 2–7 and 30 pg/ml after day of life 7.Serum interleukin-6 can be used with high accuracy to detect sepsis in neonates and very-preterm as well as very-low-birthweight infants.Interleukin-6 values display distinct cut-off values depending on the chronological age of the infant.Our article provides the first cut-off values for interleukin-6 in the first days of life in neonates.