The development of a national standardized approach for the enumeration of residual leucocytes in blood components

Background and Objectives The UK Blood Transfusion Services implemented universal leucocyte depletion of the blood supply in November 1999. To provide statistical process monitoring of these processes, automated methods were introduced to count residual leucocytes (white blood cells) in blood components. Materials and Methods Initially in the National Blood Service (NBS) England, protocols were standardized on the use of LeucoCount reagents with either Becton-Dickinson or Beckman Coulter flow cytometers. Results Standardization of protocols resulted in a decreased intersite variability of red cell samples (from 36% to 9% at a level of 11 and 10 cells/mul, respectively), and 100% of sites (n = 11) fulfilled the validation criteria. However, we also evaluated the use of alternative reagents with the result that reagents from either Becton-Dickinson or Beckman Coulter, used on either a Becton-Dickinson or Beckman Coulter flow cytometer, passed our validation criteria. Conclusions It is critical to include samples from filtered products containing white blood cells in validations of leucocyte enumeration methodology, as results may differ between methods using these samples but not using spiked or fixed material. Standardized gating strategies and optimization methods for flow cytometers are critical for obtaining equivalent results with different reagents and instruments.