Whole blood interleukin 8 and plasma interleukin 8 levels in newborn infants with suspected bacterial infection

Aim: To evaluate a new micro‐method technique for measurement of interleukin 8 in detergent‐lysed whole blood (whole blood IL‐8) applicable to capillary blood sampling as a test for bacterial infections in neonates. Methods: Whole blood IL‐8 was measured at the first suspicion of infection along with IL‐8 determined in plasma (plasma IL‐8), C‐reactive protein and blood cultures in 154 consecutive newborn infants with clinical signs of bacterial infection. Only 20 μl of whole blood were required for the new assay. Results: Blood culture‐proven infections were diagnosed in six infants and clinical infection (defined as a combination of clinical and laboratory signs) in 20 infants. 1000 pg/ml was determined as the suitable threshold for whole blood IL‐8 by ROC‐curve analysis. At that threshold, whole blood IL‐8 detected blood culture‐proven infections with a sensitivity of 83% and a specificity of 67%. The areas under the ROC curves were similar for whole blood IL‐8 and plasma IL‐8. Conclusions: Compared with plasma IL‐8, whole blood IL‐8 offers the advantages that measurements of whole blood IL‐8 require a smaller blood sample volume and are not altered by haemolysis. The diagnostic accuracy of whole blood IL‐8 remains to be studied in more detail in the future.