Delta neutrophil index and C-reactive protein: a potential diagnostic marker of multisystem inflammatory syndrome in children (MIS-C) with COVID-19.

Multisystem inflammatory syndrome in children (MIS-C) is a life-threatening hyperinflammation syndrome emerging after COVID-19. The serum delta neutrophil index (DNI) reflects the fraction of circulating immature granulocytes and is evaluated in infection and inflammation. The aim of this study is to evaluate the usefulness of DNI as a diagnostic marker in patients with MIS-C and to assess its role in determining the severity of MIS-C. This retrospective, observational study included 83 patients with MIS-C and 113 patients with COVID-19, and 102 healthy controls. C-reactive protein (CRP), the absolute neutrophil count (ANC), absolute lymphocyte count (ALC), DNI, and the platelet count were recorded. The DNI levels were 4.60 ± 5.70% in the MIS C group, 0.30 ± 0.99% in the COVID group, and 0.20 ± 0.56% in the control group (p < 0.001). According to the severity of MIS-C, the DNI level was found to be 1.22% in mild MIS-C, 4.3% in moderate MIS-C, and 5.7% in severe MIS-C. There was a statistically significant correlation between DNI levels and the severity of MIS-C. The cutoff value of DNI for predicting MIS-C was 0.45%. In the analysis of the diagnostic performance of DNI compared with CRP, ANC, ALC and platelet counts, sensitivity, specificity, positive predictive value, and negative predictive value were found to be 79.5%, 97.1%, 95.7%, and 85.3%, respectively.Conclusions: The delta neutrophil index was identified as a diagnostic marker for MIS-C such as ANC, ALC, platelet count, and CRP. DNI levels in hemogram analysis may guide clinicians in determining the diagnosis and severity of MIS-C. What is Known: • Although CRP, sedimentation, ALC, ANC, platelet count, sodium, and albumin are used as first step tests, there is no specific laboratory marker used in the diagnosis of MIS C. • The serum delta neutrophil index (DNI) reflects the fraction of circulating immature granulocytes and is elevated in infection and inflammation. What is New: • DNI is a promising and easily accessible marker that can be used with other markers in the diagnosis and determines the severity of MIS C. • DNI is an easily accessible, inexpensive, and dynamic marker and its levels in simple hemogram analysis will guide pediatricians in determining the diagnosis and severity in MIS C.