Role of serum procalcitonin in differentiating disease flare and systemic bacterial infection among febrile children with known chronic rheumatic diseases: a cross-sectional study.

Objectives: To evaluate the role of serum procalcitonin (PCT) as a diagnostic tool to differentiate bacterial sepsis from flare-ups during febrile episodes in children with known rheumatic disorders compared to other inflammatory markers like C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR).

Methods: Previously diagnosed patients with known rheumatic disorders presenting in emergency or outpatient departments with febrile episodes were included in the study. Blood samples were collected upon admission to test for signs of infection, including serum PCT levels with routine laboratory and radiological tests. Patients with juvenile idiopathic arthritis (JIA) and systemic lupus erythematosus (SLE) were stratified using the Juvenile Arthritis Disease Activity Score (JADAS-27) and SLE Disease Activity Index (SLEDAI) respectively. Patients without bacterial focus with high disease activity were included in the flare-up group and the rest in the sepsis cohort. The diagnostic value of PCT was calculated using receiver operating characteristic (ROC) curve analysis.

Results: In the study (N=73), 41 (56.2%) patients were previously diagnosed with JIA and 28 (38.3%) had SLE. 38 patients had definite evidence of sepsis and 35 had disease flare-ups as per respective disease activity scores. There was a significant difference in PCT and CRP among the flare-up and sepsis groups. For detecting sepsis, the area under curve (0.959), sensitivity (94.7%), and specificity (74.3%) of PCT at a cut-off of 0.275 ng/mL were significantly better than those of CRP.

Conclusion: PCT is a better diagnostic test than CRP or ESR during febrile episodes in differentiating flare-ups from infection and PCT >0.275 ng/mL indicates bacterial infection with good specificity and sensitivity in children with low disease activity.