Flow cytometric validation of automated differentials in pediatric patients

Manual differential white blood cell (WBC) counting has been considered the gold standard and is routinely used to validate differentials obtained with other methodologies. To validate the accuracy of automated lymphocyte counts, we compared 2-part differentials using a Coulter HmX hematology analyzer and a Coulter XL flow cytometer to analyze 57 pediatric samples with WBC counts ranging from 0.7 k to 33.4 k. These data were compared with manual differential counts. We found excellent correlation between the two automated lymphocyte and monocyte counting methods that surpassed the manual correlations, indicating manual lymphocyte or monocyte counts are unnecessary in the setting of quality scatterplots. To evaluate the use of automated differentials for our most labor-intensive cases (low WBCs, which frequently require manual differentials) we then compared 3-part differentials using the HmX hematology analyzer and flow cytometer for 51 samples with total WBC < or = 1.1 x 10(9)/L. Manual differentials (< or = 100-cell counts) were available on 27 samples. Although the correlations for manual versus automated or flow differentials were good for all cell types, the correlation between the two automated methods was better, irrespective of the hematology analyzer scatterplot quality. Preliminary data provide additional evidence that automated differentials in samples with WBC of < or = 1.1 x 10(9)/L are acceptable for reporting, thus saving technologist time and improving patient care by decreasing the resulting turnaround time. These studies suggest that comparison with a standardized procedure like flow cytometry would be a better method for validation of automated differentials than comparison with the less precise, more laborious manual differential.