The United Kingdom National External Quality Assessment Scheme gating and standardization strategy for use in residual WBC counting of WBC-reduced blood components.
BACKGROUND: Major causes of interlaboratory variation in low-level WBC counting are the gating strategies and staining methods employed. To overcome these limitations, a stable low-level WBC control preparation (termed daily run control [DRC]) was developed that when coupled with a new gating strategy will enable international standardization. STUDY DESIGN AND METHODS: Both a whole blood preparation (stability of more than 12 months; target WBC count of 20 cells/microL with defined fluorescence values) and a new gating strategy were developed and used with a staining kit (LeucoCOUNT [Becton Dickinson BioSciences] providing the basis for standardization). These were then combined and used to crosscalibrate seven different flow cytometers. After standardization with the DRC, comparative studies were undertaken with fresh samples with a WBC range of <1 to 60 cells per microL. RESULTS: The developed gating strategy enabled the DRC WBCs to be positioned to within four channels of the expected target fluorescence 1 value (2.3% variation) and within three channels of the target fluorescence 2 value (0.7% variation) on all evaluated instruments. Subsequent analysis of any sample meant that the WBCs always occupied the same "sample space," irrespective of flow cytometer platform and without the need for repositioning of the analysis region and/or gate. CONCLUSION: The cross calibration and standardization of flow cytometers used for low-level WBC counting (irrespective of platform) are attainable with this United Kingdom National External Quality Assessment Scheme strategy. Its adoption should reduce interlaboratory CVs and provide a practical approach for the rapid identification of operator and machine problems.