Methods for counting residual leukocytes in leukocyte-depleted plasma-a comparison between a routine hematology instrument, the Nageotte chamber, flow cytometry, and a fluorescent microscopy analyzer

Comparative study of quality of leukoreduced packed red blood cell units as assessed by nageotte hemocytometry and flow cytometry

PURPOSE

Assessment of residual white blood cell (rWBC) count is vital to ascertain the quality of leukodepleted (LD) blood components. Automated cell analyzers lack the sensitivity for the assessment of very few leukocytes as found in LD blood components. Flow Cytometry (FC) based methods and Nageotte hemocytometer are the most commonly used techniques for this purpose. The objective of this study was to compare the use of Nageotte hemocytometer and FC for quality control of LD red blood cell units.

MATERIALS AND METHODS

A prospective, observational study was conducted in the Department of Immunohematology and Blood Transfusion of a tertiary care center from September 2018 to September 2020. About 303 LD-packed red blood cell units were tested by FC and Nageotte hemocytometer for rWBCs.

RESULTS

The number of rWBC (mean) detected by flow cytometer and Nageotte's hemocytometer was 1.06 ± 0.43 white blood cell (WBC)/μL and 0.67 ± 0.39 WBC/μL, respectively. Coefficient of variation was 58.37% by Nageotte hemocytometer method and 40.46% by FC. Linear regression analysis did not show any correlation (R2= 0.098, P = 0.001) whereas Pearson's correlation coefficient showed a weak relation (r = 0.31) between the two methods.

CONCLUSION

Flow cytometric technique provides a more precise and accurate objective tool compared to Nageotte hemocytometer which is labor intensive, time consuming, and prone to errors arising out of subjectivity along with reported underestimation bias. In the absence of adequate infrastructure, resources, and trained workforce, Nageotte hemocytometer method is a reliable alternative. Nageotte's chamber could be best used in the resource-constrained setup as it offers a relatively inexpensive, simple, and viable means to enumerate rWBCs.

An evaluation of a volumetric method for the flow cytometric determination of residual leukocytes in blood transfusion units

The removal of leukocytes from blood components helps to prevent or reduce some adverse reactions that occur after blood transfusions. The implementation of the leukodepletion process in the preparation of blood units requires quality control, consisting of a reliable cell counting method to determine residual leukocytes in blood components. The most widely used methodology is a flow cytometric bead-based counting method. To avoid the need for commercial counting beads, we evaluated a volumetric counting method of leukocyte enumeration. A total of 160 specimens of leukodepleted plasma, red cell and platelet units, as well as 58 samples of commercially available controls containing different concentration levels of leukocytes, were included in the study. The conventional quality control method using the bead-based counting method performed with the FACSCalibur flow cytometer was compared to the bead-based counting method and the volumetric counting method performed with the MACSQuant 10 flow cytometer. Our results show that the MACSQuant bead-based method, as well as the volumetric MACSQuant method, meet the sensitivity requirements of residual leukocyte enumeration when compared to the gold standard, bead-based FACSCalibur method. We conclude that the volumetric method can be a substitute for the bead-based counting of residual leukocytes in a variety of blood components.

Evaluation of urine dipsticks for quality control of residual erythrocytes and leukocytes in leukocyte-depleted donor plasma

Currently used methodologies for quality control of residual leukocytes and erythrocytes in leukocyte-depleted plasma are either expensive or time-consuming. It has been proposed that urine dipsticks could be used as a screening method for residual erythrocytes. The aim was, therefore, to evaluate if urine dipsticks could be used to detect residual erythrocytes and also residual leukocytes in leukocyte-depleted plasma. Dilution series ranging over the decision limits for residual erythrocytes and leukocytes were prepared. Positive, negative and overall agreements, as well as the precision and joint frequency distributions, were calculated for five dipstick analyzers and their corresponding dipsticks. Twenty-four consecutive leukocyte-depleted donor plasma samples were also tested. None of the dipstick analyzers had both a high positive and a high negative agreement. Accordingly, none of the analyzers were able to discriminate between cell concentrations close to the decision limits. The inconsistency count revealed differences in precision between the dipstick analyzers. In the 24 consecutive donor samples, no significant correlation between the dipstick analyzers and the reference methods were found. In conclusion, urine dipsticks are not suitable for quality control of residual leukocytes and erythrocytes in leukocyte-depleted donor plasma.

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 a routine hematology analyzer for quality control of leukoreduced plasma

BACKGROUND

Quality control of residual white blood cells (WBCs) and red blood cells (RBCs) in leukoreduced plasma is mandatory. Although technological advances have been made, analysis of quality controls using routine hematology analyzers has not generally been introduced. The aim of this study was to evaluate if the routine hematology analyzer Sysmex XN-10, (Sysmex Nordic ApS) could be used for quality control of residual WBCs and RBCs in leukoreduced plasma.

STUDY DESIGN AND METHODS

Linearity, accuracy, and precision were established for two Sysmex XN-10 analyzers using spiked donor plasma. ADAM rWBC (NanoEnTek) and manual counting in the Bürker chamber (NanoEnTek) were reference methods for WBCs and RBCs, respectively. Twenty-five consecutive leukoreduced donor plasma samples were also tested.

RESULTS

For WBCs, the linearity criteria were met for the ADAM rWBC, but not for the Sysmex XN-10 instruments. Precision on both Sysmex XN-10 instruments was accurate only at 6 cells/μL, and accuracy was consistently acceptable only at 5 to 6 cells/μL. The precision and accuracy of the ADAM rWBC were acceptable at 2 to 6 cells/μL. For RBCs, both Sysmex XN-10 instruments and manual counting in the Bürker chamber were linear and fulfilled the precision criteria. Accuracy was acceptable for both Sysmex instruments at 6 to 12 × 10⁹ WBCs/L but fluctuated within the study's measuring range for the Bürker chamber. No false-positive results were seen in the 25 consecutive donor plasma samples tested.

CONCLUSION

For quality control purposes of leukoreduced plasma, the Sysmex XN-10 analyzer is suitable for the enumeration of residual RBCs but not of residual WBCs.

Non-electrical powered continuous cell concentration for enumeration of residual white blood cells in WBC-depleted blood using a viscoelastic fluid

White blood cells (WBCs) are one of the critical components whose number has to be reduced before blood transfusion, failing which adverse transfusion effects may occur in patients. However, due to the extremely low concentration of residual WBCs (r-WBCs) in WBC-depleted blood, it is difficult to quantify r-WBCs accurately without using expensive and voluminous instruments. Therefore, the development of a continuous cell concentration technique is required to produce a countable number of cells from rare cells, which cannot normally be detected. In this paper, we present a viscoelastic microfluidic device for sheathless, continuous concentration of WBCs. The device performance was evaluated using polystyrene particles with different sizes at various flow rate conditions in a non-Newtonian fluid compared to a Newtonian fluid. Large particles with a blockage ratio higher than 0.1 were tightly focused at the center and collected at the center outlet with a 98% collection ratio. Meanwhile, the viscosity effect of lysed blood samples with various hematocrits was considered. Finally, diluted WBCs with various dilution ratios were concentrated by ~18-fold and continuous concentration of WBCs in lysed blood samples was performed using a non-electrical powered hand pump sprayer. Without using an external power source, center-focused WBCs were collected at the center outlet at approximately 150 μl/min and the final number of WBCs was increased to 1.8 × 10⁴ cells/ml from undetectable levels.