Interpretation of atypical patterns encountered when using a flow cytometry-based method to detect residual leukocytes in leukoreduced red blood cell components

Evaluation of platelets componentized with the Reveos Automated Blood Processing System and stored for 7 days at room temperature in a non-Di(2-ethylhexyl) phthalate (DEHP) platelet pooling set

BACKGROUND

Platelet concentrates (PCs) used for transfusion can be produced by apheresis or derived from whole blood (WB). The Reveos device is the first US Food and Drug Administration-approved automated blood processing system that can produce PCs. In this work, we evaluated the quality and function of Reveos-collected PCs stored for 7 days at room temperature.

STUDY DESIGN AND METHODS

WB was collected from healthy donors and componentized on the day of collection (Fresh) or after an overnight hold (Overnight). PCs were produced (n = 7 Fresh; n = 6 Overnight), stored at room temperature in plasma, and evaluated on days 1 and 7 for quality metrics, platelet activation, clot formation, and aggregation response.

RESULTS

Platelet count was comparable between Fresh and Overnight PCs. A drop in pH was reported in Fresh day 7 PCs (p < .001, vs. day 1) but not in Overnight. Overnight units displayed the lowest levels of P-selectin expression (p = .0008, vs. day 7 Fresh). Reduced clot strength and increased lysis were observed in both Fresh and Overnight units on day 7 (vs. day 1). Overnight-hold PCs resulted in the highest clot strength on day 7 (p = .0084, vs. Fresh). No differences in aggregation were reported between groups.

CONCLUSION

Reveos-processed PCs produced from overnight-hold WB performed better in hemostatic function assays and displayed reduced activation compared to fresh WB-derived PCs, although both PC groups maintained platelet quality throughout storage. Utilization of overnight WB for PC preparation with Reveos holds promise as an alternative method of producing platelets for transfusion purposes.

The use of a hematology analyzer with a new generation of software as an alternative to flow cytometry for enumerating residual white blood cells in blood components

BACKGROUND

Leukoreduction of blood components was implemented to reduce transfusion‐associated risks. The detection level for residual white blood cells (rWBCs) required to demonstrate leukoreduction was originally considered too low for hematology analyzers. Developments enabling cell counts in body fluids have, however, renewed interest in rWBC counting. An assessment of Sysmex XN hematology analyzers with software offering automated rWBC enumeration intended for use on blood components was performed.

STUDY DESIGN AND METHODS

Performance characteristics were determined using platelet, red blood cell (RBC), and plasma samples spiked with WBCs. Subsequently, components (platelets, n = 1367; and plasma, n = 80) were tested and results compared with flow cytometry, to monitor leukoreduction efficiency to a level of less than 1 × 10⁶/unit. Components identified by flow cytometry as having poor leukoreduction, exceeding this limit, were also tested (platelets, n = 3; and RBCs, n = 10).

RESULTS

Linearity studies up to 32 WBCs/μL showed good correlation between observed and expected results (R² > 0.9996). Precision analysis gave an average limit of quantitation of 2 WBCs/μL with coefficients of variation less than 20%. Average carryover was 0.1%. Plain sample tubes were a source of aberrant results with routine components. Using ethylenediaminetetraacetic acid tubes the analyzer gave results greater than 1 × 10⁶/unit in 2.7% of cases compared with 1.4% by flow cytometry, but overall results were within specification, with more than 90% of components having rWBC values below the limit. All incidences of poor leukoreduction, with flow cytometry results greater than 13 rWBCs/μL were correctly identified, with an excellent correlation between results (R² = 0.9818).

CONCLUSION

The analyzer demonstrated acceptable performance characteristics for enumeration of rWBCs; consequently, additional multisite evaluations are warranted.

http://onlinelibrary.wiley.com/doi/10.1111/trf.15642/full

Evaluation of droplet digital PCR for quantification of residual leucocytes in red blood cell concentrates

BACKGROUND AND OBJECTIVES

Enumeration of residual white blood cells in leucoreduced blood components is essential part of quality control. Digital PCR has substantially facilitated quantitative PCR and was thus evaluated for measurements of leucocytes.

MATERIALS AND METHODS

Target for quantification of leucocytes by digital droplet PCR was the blood group gene RHCE. The SPEF1 gene was added as internal control for the entire assay starting with automated DNA extraction. The sensitivity of the method was determined by serial dilutions of standard samples. Quality control samples were analysed within 24 h, 7 days and 6 months after collection. Routine samples from leucodepleted red blood cell concentrates (n = 150) were evaluated in parallel by flow-cytometry (LeucoCount) and by digital PCR.

RESULTS

Digital PCR reliably detected at least 0·4 leucocytes per assay. The mean difference between PCR and flow-cytometric results from 150 units was -0·01 (±1·0). DNA samples were stable for up to at least six months. PCR measurement of leucocytes in samples from plasma and platelet concentrates also provided valid results in a pilot study.

CONCLUSION

Droplet digital PCR to enumerate leucocytes offers an alternative for quality control of leucoreduced blood products. Sensitivity, specificity and reproducibility are comparable to flow-cytometry. The option to collect samples over an extended period of time and the automatization introduce attractive features for routine quality control.

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.

The effect of whole-blood storage time on the number of white cells and platelets in whole blood and in white cell-reduced red cells

BACKGROUND

Whole blood (WB) can be stored for some time before it is processed into components. After introduction of universal white cell (WBC) reduction, it was observed that longer WB storage was associated with more residual WBCs in the WBC-reduced red cells (RBCs). Also, weak propidium iodide (PI)-positive events were observed in the flow cytometric WBC counting method, presumably WBC fragments. The effect of storage time on the composition of WB and subsequently prepared WBC-reduced RBCs was studied.

STUDY DESIGN AND METHODS

WB was collected in bottom-and-top collection systems with inline filters, obtained from Baxter, Fresenius, or MacoPharma. Units were stored at room temperature and separated into components in 4-hour intervals between 4 and 24 hours after collection. RBCs were WBC-reduced by inline filtration (approx. 50/group).

RESULTS

Platelet (PLT) counts were lower in WB stored for 4 to 8 hours compared to 20 to 24 hours (mean +/- SD): 79 +/- 31 versus 102 +/- 30 for Baxter (p < 0.01); 91 +/- 31 versus 101 +/- 35 for Fresenius (not significant); and 73 +/- 47 versus 97 +/- 31 (all x 10(9) per unit) for MacoPharma (p < 0.01), respectively. The median residual WBC counts in WBC-reduced RBCs for WB stored for 4 to 8 and 20 to 24 hours were 0.03 versus 0.17 for Baxter (p < 0.001), 0.00 versus 0.06 for Fresenius (p < 0.001), and 0.13 versus 0.26 (all x 10(6) per unit) for MacoPharma (not significant), respectively. All WBC-reduced RBCs contained fewer than 5 x 10(6) WBCs per unit. A longer storage time of WB was associated with more weak PI-positive events, irrespective of the filter.

CONCLUSION

Longer storage of WB before processing results in counting higher numbers of PLTs in WB, higher numbers of WBCs in WBC-reduced RBCs, and more weak PI-positive events.

[Residual leukocyte counting in plasma by a real-time genomic amplification assay]

BACKGROUND

Systematic plasma leukoreduction, which was introduced in France in April 1st 2001, has given rise to more sensitive methods for residual leukocytes counting. The technologies in application at this moment (Nageotte hemocytometers and flow cytometry methods) have been modified by a thirty fold sample concentration prior to analysis, inducing frequent downgrading of the plasma unit. So, in order to improve the detection threshold, we developed a more sensitive assay using "Real-Time Polymerase Chain Reaction" technology.

MATERIALS AND METHODS

Real-time polymerase chain reaction was performed on a highly conserved HLADQalpha1 gene sequence. In order to determine the analytical performances of the method (accuracy, sensitivity, linearity and specificity) serial dilutions series ranging from 10(4) to 1 cells/ml were performed. A total of 18 series were prepared from three leukocyte stock solutions, by 1 in 10 serial dilutions in three plasmas completely devoided of white cells (called negative plasmas). To examine the specificity of the assay two negative controls were analyzed in each run.

RESULTS

a sensitivity of 10 cells/ml (10(4) leukocytes/l) was achieved and the assay was linear between 10 and 10(4) cells/ml. The slope (-3.72) of the average standard curve calculated from all series, showed an amplification yield of 92.85%.

CONCLUSION

we developed a quantitative assay for residual leukocytes in leukodepleted plasma, that agreed with the quality control requirement specifications.

Low propidium iodide intensity in flow cytometric white blood cell counting as a marker of cell destruction?

BACKGROUND

Residual white blood cells (WBC) in filtered blood products were investigated with flow cytometry. Frequently two distinct populations with different propidium iodide (PI) intensities can be found. The aim of this study was to specify a population with low PI intensity and discuss it as a marker of ongoing cell destruction and their possible impact on cytomegalovirus safety.

STUDY DESIGN AND METHODS

Buffy coat-depleted red blood cells were filtered with an in-line filtration set (LCR5, MacoPharma) after 4 hours (LCR5/4 hr) and 16 hours (LCR5/16 hr) of storage, and whole blood was filtered with a whole-blood filtration set (LST1, MacoPharma [LST1/4 hr]). The population with low PI intensity was sorted with a flow cytometer and prepared for transmission electron microscopy.

RESULTS

The absolute count obtained in the low-PI-intensity area before filtration was significantly different comparing LCR5/4 hr (11.5 x 10(6) +/- 6.84 x 10(6) and 0.12 x 10(6) +/- 0.1 x 10(6)/unit) and LCR5/16 hr (69.3 +/- 42.12 and 0.06 +/- 0.05; p < 0.002). By use of LST1/4 hr no difference was found compared to LCR5/4 hr after filtration (0.12 +/- 0.09 vs. 0.12 +/- 0.1), but a significant difference was found when comparing the results before filtration (1.25 +/- 0.41 vs. 11.5 +/- 6.84; p < 0.02). Electron microscopy revealed that the sorted population consisted of predominantly cell and nuclear fragments.

CONCLUSIONS

Events found in the low-PI-intensity area are not WBCs but partially degraded DNA coming from ongoing cell destruction during extended storage. Our results provide evidence that the absolute count of events found in the low-PI-intensity area can be used as a semiquantitative marker of WBC destruction.

EliCell assay for the detection of released cytokines from eosinophils

Eosinophils contain several preformed cytokines within their specific granules. Therefore, without requiring them in de novo synthesis of cytokines, eosinophils can release quantities of granule-derived cytokines by highly regulated mechanisms. However, eosinophil "degranulation" is poorly understood, in part, because available methodologies did not appear appropriate for analyzing vesicular mobilization and transport of eosinophil granular contents. The EliCell assay is a microscopic methodology substantially modified from other techniques employed to detect cytokine release (i.e., ELISPOT). The method is a dual antibody capture/detection system in which viable eosinophils are incubated in a solid streptavidin-conjugated agarose matrix, which contains a biotinylated capture antibody against the cytokine of interest. Released cytokine is detected around non-permeabilized eosinophils with a separate fluorochrome-labeled detection antibody. Thus, the EliCell system captures and detects extracellular cytokines at the site of their release from eosinophils. As examples, we have used EliCell essays to detect the selective release of either IL-4 or IL-12 cytokines found preformed in eosinophils-from eotaxin- or anti-CD9-stimulated eosinophils, respectively. With appropriate pairs of antibodies, any preformed cytokine found into eosinophil granules could be studied and the mechanisms of their secretion evaluated by using the EliCell assay.