Performance of an Automated Immature Granulocyte Count
Performance of an Automated Immature Granulocyte Count
Neonatologists use immature granulocytes (IG) in manual differential counts as an indicator of sepsis. This study was designed to compare the predictive ability of automated vs manual IG counts for neonatal sepsis. Infants undergoing sepsis evaluation were identified prospectively for study if a CBC count was obtained in temporal proximity to the blood culture. Automated IG counts were obtained from the research software of the Sysmex XE-2100 (Sysmex, Kobe, Japan). Manual average IG counts were obtained from two 100-cell manual differential counts independently performed by a technologist and a hematopathology resident. A comparative analysis of manual and automated IG counts showed considerable overlap of ranges. The highest positive blood culture rate occurred in the nonneutropenic preterm subset of infants older than 7 days (21/55 [38%]). For these infants, elevated IG counts by manual and automated methods were associated significantly with positive blood culture results (odds ratio, manual, 3.74; odds ratio, automated, 3.63), albeit with low sensitivity.
The detection of a granulocytic left shift in manual differential counts often is used as an indicator of sepsis in infants. A left shift traditionally has been defined as an elevated neutrophil band count or an elevated immature/total granulocyte (I/T) ratio. However, in the pertinent published literature, the validity of these granulocyte parameters as predictors of neonatal sepsis continues to be controversial owing to the use of inconsistent criteria for defining left shift and sepsis. The statistical imprecision of 100-cell manual differential counts combined with subjective morphologic criteria and interobserver variation make band counts unreliable. In addition, it is extremely difficult to determine reference ranges for immature granulocytes (IGs) in infants because these cells undergo rapid fluctuation during the first 5 days of postnatal life, and it is difficult to obtain samples from infants. Many earlier studies of diagnostic tests in neonatal sepsis have had flaws in study design and statistical analysis. In a systematic review of the literature on diagnostic testing for neonatal sepsis, Fowlie and Schmidt concluded that "[e]ven in rigorous studies, the reported accuracy of the tests varies enormously and they are of limited value in the diagnosis of infection in this population."
Despite controversy about the predictive value of band counts and I/T ratios, their use persists in clinical practice. A more reliable method for determining the presence of a granulocytic left shift would be highly desirable. Recently, the ability to count IGs by automated flow-through hematology analyzers has been developed. Automated IG counts offer the potential advantages of improved accuracy, precision, and turnaround time compared with manual differential counts. The purpose of the present study was to compare the predictive ability of the manual IG count and the automated IG count produced by the Sysmex XE-2100 hematology analyzer (Sysmex, Kobe, Japan) for the diagnosis of neonatal sepsis.
Neonatologists use immature granulocytes (IG) in manual differential counts as an indicator of sepsis. This study was designed to compare the predictive ability of automated vs manual IG counts for neonatal sepsis. Infants undergoing sepsis evaluation were identified prospectively for study if a CBC count was obtained in temporal proximity to the blood culture. Automated IG counts were obtained from the research software of the Sysmex XE-2100 (Sysmex, Kobe, Japan). Manual average IG counts were obtained from two 100-cell manual differential counts independently performed by a technologist and a hematopathology resident. A comparative analysis of manual and automated IG counts showed considerable overlap of ranges. The highest positive blood culture rate occurred in the nonneutropenic preterm subset of infants older than 7 days (21/55 [38%]). For these infants, elevated IG counts by manual and automated methods were associated significantly with positive blood culture results (odds ratio, manual, 3.74; odds ratio, automated, 3.63), albeit with low sensitivity.
The detection of a granulocytic left shift in manual differential counts often is used as an indicator of sepsis in infants. A left shift traditionally has been defined as an elevated neutrophil band count or an elevated immature/total granulocyte (I/T) ratio. However, in the pertinent published literature, the validity of these granulocyte parameters as predictors of neonatal sepsis continues to be controversial owing to the use of inconsistent criteria for defining left shift and sepsis. The statistical imprecision of 100-cell manual differential counts combined with subjective morphologic criteria and interobserver variation make band counts unreliable. In addition, it is extremely difficult to determine reference ranges for immature granulocytes (IGs) in infants because these cells undergo rapid fluctuation during the first 5 days of postnatal life, and it is difficult to obtain samples from infants. Many earlier studies of diagnostic tests in neonatal sepsis have had flaws in study design and statistical analysis. In a systematic review of the literature on diagnostic testing for neonatal sepsis, Fowlie and Schmidt concluded that "[e]ven in rigorous studies, the reported accuracy of the tests varies enormously and they are of limited value in the diagnosis of infection in this population."
Despite controversy about the predictive value of band counts and I/T ratios, their use persists in clinical practice. A more reliable method for determining the presence of a granulocytic left shift would be highly desirable. Recently, the ability to count IGs by automated flow-through hematology analyzers has been developed. Automated IG counts offer the potential advantages of improved accuracy, precision, and turnaround time compared with manual differential counts. The purpose of the present study was to compare the predictive ability of the manual IG count and the automated IG count produced by the Sysmex XE-2100 hematology analyzer (Sysmex, Kobe, Japan) for the diagnosis of neonatal sepsis.
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