Diagnostic accuracy of C-reactive protein and procalcitonin against blood culture in neonatal sepsis, with ROC/logistic regression analysis and antimicrobial susceptibility pattern: a prospective observational study in a South Indian neonatal intensive care unit

Abstract Background Neonatal sepsis presents with non-specific clinical signs, and blood culture, the diagnostic gold standard, is slow with limited sensitivity. C-reactive protein (CRP) and procalcitonin (PCT) have been proposed as faster adjuncts, but their discriminatory performance, independent predictive value, and accompanying resistance patterns vary by setting. We evaluated CRP and PCT against blood culture, identified independent predictors of culture positivity, and characterised the bacteriological and antimicrobial susceptibility profile in neonates with suspected sepsis at a South Indian tertiary-care hospital. Methods In this prospective study, 200 neonates admitted to a South Indian tertiary-care NICU with clinical signs of sepsis were enrolled over 11 months. Blood was collected before antibiotics for culture, complete blood count, CRP, and PCT. Isolates were tested for antimicrobial susceptibility and ESBL production by CLSI-recommended methods. ROC analysis compared the discriminatory performance of PCT, platelet count, and white cell count for culture positivity, and multivariable logistic regression identified independent predictors. Results Blood culture was positive in 61/200 neonates (30.5%). PCT showed the highest discriminatory performance (AUC 0.885, 95% CI 0.824–0.946), outperforming platelet count (AUC 0.630) and white cell count (AUC 0.532, not different from chance), with sensitivity 88.5% and specificity 84.9%. On multivariable regression (Hosmer-Lemeshow P = 0.3235; model AUC 0.902), PCT positivity was the strongest independent predictor of culture positivity (adjusted odds ratio 44.25, 95% CI 16.27–143.9), and assisted vaginal delivery was independently associated (adjusted odds ratio 5.05, 95% CI 1.57–18.25). Platelet counts were paradoxically higher, not lower, in culture-positive (P = 0.0034) and preterm neonates (P = 0.0305). Gram-negative bacilli accounted for 70.5% of isolates, led by Klebsiella pneumoniae (54.1%); ESBL production was confirmed in 36.4% of K. pneumoniae and 50.0% of E. coli isolates. Conclusions Procalcitonin substantially outperformed CRP, platelet count, and white cell count both as a single marker and as an independent predictor of culture-positive neonatal sepsis, while Klebsiella pneumoniae with a high ESBL burden dominated the bacteriological profile. These findings support incorporating procalcitonin, rather than platelet count, into local sepsis screening and stewardship pathways. Trial registration: Not applicable (observational study; no intervention was assigned).