An Evaluation of Novel Inflammatory Biomarkers in Children with Kingella kingae Osteoarticular Infections.

Kingella kingae is now recognised as the leading cause of osteoarticular infections (OAIs) in young children. Because these infections typically produce mild symptoms and a weak inflammatory response, early diagnosis remains challenging. Complete blood count-derived immune-inflammatory biomarkers (IIBs) have recently gained interest as accessible, low-cost indicators of systemic inflammation, with potential diagnostic value in several fields, including oncology, rheumatology, cardiology, and infectious diseases. This study therefore aimed to assess whether IIBs could support the screening of K. kingae OAIs. We retrospectively reviewed the medical records of 209 children admitted to our hospital between 2007 and 2025 with confirmed or highly suspected K. kingae OAIs. Complete blood counts were analysed for each patient, including leukocyte subtypes such as neutrophils, lymphocytes, monocytes, eosinophils, and basophils. We then calculated biomarkers (NLR, MLR, PLR, SII, SIRI, and PIV) and interpreted them using age-adjusted reference values. As expected, most children were younger than 48 months, and septic arthritis was the predominant clinical presentation. Classical acute-phase reactants (WBC, CRP, and ESR) were frequently normal or only mildly elevated. Likewise, most IIBs remained within or near reference ranges; the platelet-to-lymphocyte ratio was the most commonly abnormal marker, exceeding the threshold in only 59.3% of patients. These results indicate that, like conventional inflammatory markers, CBC-derived IIBs have limited standalone screening utility for K. kingae OAIs. Further studies are needed to determine whether systemic IIBs can help distinguish OAIs caused by K. kingae from those caused by pyogenic bacteria.