Background Therapeutic hypothermia (HT) delays the cytokine response in infants with neonatal encephalopathy (NE).

Objective To determine if HT delayed the C-reactive protein (CRP) response and altered white blood cell (WBC), neutrophil and platelet count course during the first week of life in infants with NE.

Design Retrospective cohort study.

Setting Regional neonatal intensive care unit, UK.

Patients 104 term infants with NE (38 normothermia (NT) and 66 HT) born between 1998 and 2010. Infants not exposed to prenatal sepsis risk factors were classified as group ‘A’ and exposed infants to group ‘B’. CRP >10 mg/L was defined as significant response.

Main outcome measures Time to CRP >10 mg/L, peak CRP, WBC, neutrophil and platelet count.

Results Blood cultures were negative in all the infants. In babies who had CRP response, HT delayed time to CRP >10 mg/L (median (95% CI): group A, HT: 36 h (28.3 to 48.0); NT: 24 h (0.0 to 24.0); p=0.001; group B, HT: 30 h (15.2 to 56.8); NT: 12 h (0.0 to 24.0); p=0.009) and time to peak CRP (median (95% CI): group A, HT: 60 h (60.0 to 72.0); NT: 36 h (0.0 to 48.0); p=0.001; group B, HT: 84 h (62.1 to 120.0); NT: 24 h (0.0 to 36.0); p=0.001). Compared with NT, HT was associated with reduction in slope of CRP elevation by 0.5 (95% CI 0.04 to 0.97), WBC by 2.18×10⁹/L (95% CI 0.002 to 4.35) and platelet count by 32.3×10⁹/L (95% CI 2.75 to 61.8) independent of exposure to sepsis risk, meconium aspiration and severity of asphyxia.

Conclusions Therapeutic hypothermia delayed the initiation of CRP and its peak response, and depressed the WBC and platelet count compared with NT.