Statistical process monitoring of WBC-reduced blood components assessed by two types of software

Flow cytometric determination of residual white blood cell levels in preserved samples from leukoreduced blood products

BACKGROUND

In preparation for a proposed consolidated testing service, Canadian Blood Services undertook the evaluation of a commercial test kit for the enumeration by flow cytometry of residual white blood cells (rWBCs) present in preserved samples recovered from leukoreduced (LR) blood and platelet products.

STUDY DESIGN AND METHODS

The stability of preserved WBCs, the equivalency of WBCs used for spiking, test method precision, specificity, reliability, accuracy, and sensitivity were investigated. For comparative purposes, WBC counts were also determined by Nageotte as well as by flow cytometry.

RESULTS

WBCs were stable up to 4 weeks at room temperature for all components by either method. Within methods, no differences were observed due to the source of WBC used for spiking purposes. By either method, test precision was acceptable (<20% coefficient of variation) and of similar reliability at a target value of 10 +/- 5 WBCs per microL. The flow cytometric method was shown to be more specific and accurate than the Nageotte method. Sensitivity by either method was 0.1 WBCs per microL. On average, Nageotte counts were lower than those observed by flow cytometry.

CONCLUSIONS

These results demonstrate that WBCs in WBC stabilizing solution-treated samples from LR blood components were stabilized up to 4 weeks at room temperature and that rWBC determinations made with a WBC enumeration kit by flow cytometry have the required precision, specificity, reliability, and accuracy in the relevant test range. This validated WBC stabilization and flow cytometric counting method is considered acceptable as part of a quality control program for leukoreduced blood products.

A novel approach to managing variation: outpatient therapeutic monitoring of calcineurin inhibitor blood levels in liver transplant recipients

OBJECTIVE

To apply the principles of statistical process control (SPC) to manage calcineurin inhibitor (CNI) blood levels. We hypothesized that the use of SPC would increase the proportion of CNI blood levels in the target range.

STUDY DESIGN

The study population consisted of 217 patients more than 3 months after liver transplantation. After demonstration of proof of concept using the rapid cycle improvement process, SPC was applied to the entire population. The change package included definition of target ranges for CNI, implementation of a web-based tool that displayed CNI blood levels on a control chart, and implementation of a protocol and a checklist for management of CNI blood levels. The principal outcome measure was the proportion of CNI blood levels in the target range.

RESULTS

In the pilot study, the proportion of CNI blood levels in the target range increased from 50% to 85%. When the protocol was spread to the entire population, the proportion of drug levels in the target range increased to 77% from 50% (P < .001), whereas the range of CNI levels decreased. The rate of allograft rejection did not change.

CONCLUSIONS

Utilization of SPC increased the proportion of CNI blood levels in target range. These observations may be applicable to the care of other chronic healthcare problems.

Universal leucodepletion: an overview of some unresolved issues and the highlights of lessons learned

Universal leucodepletion (ULD) has been introduced in several countries based on the evidence that selective leucodepletion improves the clinical safety of blood components and based on animal studies that TSE infectivity is 5-7 times higher in the buffy coat than in plasma. Therefore it is perceivable that the removal of the buffy coat, by filtration, removing both leucocytes and platelets, may prove beneficial in reducing the potential risk of transmission of variant CJD by blood components. The implementation of a ULD policy has created some new requirements: Validation/standardisation of various leucodepletion processes to ensure compliance with set specifications. Standardisation/harmonisation of sampling and low leucocyte counting technologies to ensure the interchangeability of results nationally. The establishment of external quality assessment schemes on 'real' leucodepleted products where the cells come in contact with the filter matrix, to monitor the low leucocyte counting performance, nationally. Assessment of filtration-induced generation/retention of major biological response modifiers (BRM), having potential for the development of transfusion reactions. Using these approaches we have identified that, while the overall leucodepletion performance has improved following harmonisation/standardisation of the operational and counting technologies, there are still some unresolved problems and ULD alone may not provide complete protection from some viral transmission such as HTLV and CMV infections or reduction of bacterial sepsis and generation of some BRM. Moreover, ULD has not fully abrogated febrile non-haemolytic transfusion reactions (FNHTR). Therefore the key issue is not the 3-4 log(10) reduction of residual leucocytes but the design of new generation filters or leucodepletion processes with better performance characteristics, to further reduce some specific leucocyte subsets and their fragments as well as reduce the activation of coagulation/complement/kinin and inflammatory systems. Efforts should also be made to reduce the rapid development of apoptotic/necrotic cells and the residual risk associated with plasma, which often contains a vast array of BRM, responsible for residual transfusion reactions. These could only be effectively achieved by working in cooperation with the suppliers of blood component technologies. This overview briefly highlights some of the unresolved issues related to ULD, based on the experience in the UK. Technical details can be found in the reading list provided at the end.

Universal leukoreduction of cellular and plasma components: process control and performance of the leukoreduction process

Many countries in Europe and over the world are currently or will be concerned in the near future, by the implementation of universal leukoreduction (ULR) for red blood cells (RBC), platelets (PT) and now also for plasma. Recommended by several advisory committees, this decision to implement ULR must be considered as a recognition of the benefit of early leukocyte removal, and also as a precautionary measure to increase blood safety. The leukodepletion technology for RBC, PT and plasma has become increasingly more elaborated and integrated in the collection or in the component preparation process. To reach this aim and to assure that the end-products meet local specifications (1 or 5 x 10(6) residual leukocytes), a process control and validation program for leukoreduction has been described in the specific guidelines. Tested on a wide scale by a group of centers, flow cytometry is emerging as reference method for residual leukocyte enumeration. Validation protocols (linearity, precision, accuracy) have been defined in numerous national or international studies (PSL and BEST Working Party). The sensitivity of the method is greatly improved by concentration of the sample, with a detection limit equivalent to 10 cells/mL for RBC or PT, and 0.5 cells/mL for plasma. Furthermore, monitoring of the performance of the leukoreduction process includes a quality control program based on a general statistical model with a parametric or non parametric approach, sampling plan, ongoing control, process capability assessment, confidence limit, detection of failure, and estimation of the non conforming units rate.