PRACTICAL GUIDELINES FOR PROCESS VALIDATION AND PROCESS-CONTROL OF WHITE CELL-REDUCED BLOOD COMPONENTS - REPORT OF THE BIOMEDICAL EXCELLENCE FOR SAFER TRANSFUSION (BEST) WORKING PARTY OF THE INTERNATIONAL SOCIETY OF BLOOD-TRANSFUSION (ISBT)

Background: The increased use of white cell (WBC)-reduced blood compon ents has prompted many institutions to develop quality assurance progr ams directed to such component preparation processes. For consistent p reparation of WBC-reduced blood components that meet clinical needs as well as national standards, a program of process validation and contr ol should be instituted. This involves controlling key factors that af fect WBC reduction as well as periodic monitoring of the residual cell ular content of components. Practical guidelines for the implementatio n of such a program are provided. Study Design and Methods: A program involving three phases of monitoring was developed by individuals belo nging to an international working party of the International Society o f Blood Transfusion. Results: The first phase, process validation, eva luates a minimum of 20 consecutive units (a minimum of 60 units when n onparametric measurements are used) to document the successful local i mplementation of a new or substantially modified process. Ongoing proc ess control employing Levey-Jennings type control charts is used to de monstrate that the process remains stable over time. Process capabilit y assessment and conformance with standards are evaluated once residua l WBCs are counted in a sufficient number of units. This enables a fac ility to claim with a specified degree of confidence that a stated pro portion of WBC-reduced units will meet national standards. Two approac hes to determine the number of units that should be selected for count ing are presented. The first approach considers units as either accept able or not acceptable and assumes that the distribution of failed (or nonconforming) units approximates the Poisson distribution. The secon d approach takes into consideration the observed WBC content of the te sted units, with the assumption that the residual WBC content in WBC-r educed components follows a lognormal distribution. A method to assess the lognormal distribution of residual WBCs is presented. Specific ta bles based on each of these approaches are provided to guide the reade r in the design of a program that will verify conformance with any nat ional standard at specific confidence levels. The approach can be gene ralized to other process control applications. Conclusion: Guidelines are presented for process validation, process control, and assessment of conformance in the production of WBC-reduced blood components. Poli cy makers retain the responsibility to establish, on the basis of the expected use of WBC-reduced components, requirements for the frequency of testing and for the proportion of prepared units that are expected with a stated degree of confidence to meet the standards. Facilities preparing WBC-reduced components can monitor key factors that influenc e the preparation of WBC-reduced blood, can periodically assess their conformance with the standards, and can intervene to correct adverse c hanges in the process. This approach can be used to ensure the consist ent quality of WBC-reduced blood components.