Background. Leukocyte counts may influence peripheral (micro) circulation due to changes in rheology. The aim of this study was to investigate a possible association between leukocyte counts and peripheral tissue oxygenation/perfusion measured with near infrared spectroscopy (NIRS) in term and preterm neonates. Methods. In this observational study we included term and preterm neonates within the first 2 months of life, in whom peripheral tissue NIRS measurements were performed and blood samples

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... (leukocytes and C reactive protein (CRP)) taken to investigate clinical signs of infection. Tissue-oxygenation index (TOI), fractional oxygen extraction (FTEO), oxygen delivery (DO 2 ), oxygen consumption (VO 2 ) and vascular resistance (VR) were measured by NIRS and venous occlusion method. TOI, FTOE, DO 2 , VO 2 and VR were correlated to leukocyte counts on the same day and maximal CRP levels within 24 hours (CRP max). Results. In 180 infants, with a mean gestational age of 35.5±3.3 weeks, leukocyte counts were 16546± 8830/ l (median 14830; range 1790 to 67840) and CRP max was 8.0± 19.0 mg/l (median 0.0; range 0.0 to 110.0mg/l). TOI was 71.1±5.5%, FTOE 28.5±6.1%, DO 2 46.7±19.7, p= 0.005) with TOI and positively (r=0.17; p=0.029) with VR. Correlations with CRP max did not reach significance. Conclusion. We demonstrated that peripheral tissue oxygen consumption decreases and vascular resistance increases with increasing leukocyte counts.