[Within-day and between-day quality control of white blood cell differential by moving-average method]

Since its first appearance several years ago, automated blood cell analyzers capable of calculating white blood cell (WBC)-differential by flowmetric system have been widely accepted. Although these analyzers are fast and reliable, any other suitable quality control (QC) methods than Levey-Jennings (X) method have not been established yet. In this report, we provide evidence that Bull's moving-average (MA) method is extremely useful for within-day and between-day QC of WBC-differential assayed with flowmetric NE-7000 system. Monocyte(Mon) content in the control blood cells used in X method were varied among each lot, and the percentage of neutrophil(Neu) showed a tendency to decrease, while the percentage of Mon and basophil(Bas) showed a tendency to increase during storage. On the other hand, real-time QC of WBC-differential was enabled by the MA method that calculated mean value of each batch consisting of twenty samples. Within-day and between-day coefficient of variation (CV%) of WBC-differential controlled by the MA method was ranged from 5.0 for Neu to 12.5% for eosinophil(Eos) in patients' samples, and from 2.37% for Neu to 11.57% for Mon in healthy adults' samples. Therefore, we set up the limit of CV% for QC of WBC -differential by the MA method as follows: 10% for Neu, 20% for Lymphocyte, 30% for Mon, 20% for Eos and 20% for Bas. In addition, we report our experience of one occasion when sudden decrease of Mon to below the lower limit of the CV% was indicated by the MA method and suitable adjustment was made at once. The change was not detected by X method. In conclusion, the MA method is applied to real-time, daily and weekly/monthly QC of WBC-differential.