Performance of widely used acute phase markers in differentiating auto-inflammatory and autoimmune disease flares from viral and bacterial infections

Objective: This study aimed to compare the diagnostic performance of commonly used acute phase reactants—including serum amyloid A (SAA), C-reactive protein (CRP), ferritin, procalcitonin, and erythrocyte sedimentation rate (ESR)—in distinguishing autoinflammatory and- autoimmune disease flares from viral and bacterial infection. Methods: This single-center, retrospective, cross-sectional study included 160 patients aged 1 month to 18 years, divided into four disease groups (n=40 for each: AAA attack, jSLE flare, sepsis, and viral infection). Laboratory data during disease flares were recorded for each patient, and statistical comparisons were made between groups. Results: CRP, SAA, and ESR levels were significantly higher in the jSLE and sepsis groups compared to viral infections and AAA attack. Procalcitonin levels were significantly elevated only in the sepsis group. Ferritin levels were also significantly higher in both the jSLE and sepsis groups than in the viral and AAA groups. Although CRP and SAA levels were elevated during AAA attack, other biomarkers did not show significant increases. Conclusion: SAA and CRP are highly sensitive markers for inflammatory diseases. Procalcitonin showed specificity for sepsis, while ferritin may help differentiate jSLE from sepsis. Monitoring SAA alongside CRP during AAA attack may enhance diagnostic accuracy. These findings highlight the importance of interpreting acute phase reactants collectively when distinguishing between inflammatory conditions in pediatric patients.