Laboratory Assessment of Fetomaternal Hemorrhage is Improved Using Flow Cytometry

Development of multiplexed flow cytometry-based red blood cell antibody screen and identification assays

BACKGROUND AND OBJECTIVES

The purpose of this study was to develop a high-throughput method of performing red blood cell antibody screens and identification by utilizing flow cytometry and intracellular dyes to allow a multiplexed assay where three-cell screens can be performed in a single test well and 11-cell panels in three test wells.

MATERIALS AND METHODS

Reagent red blood cells were labelled using Violet Proliferation Dye 450 (V450) and Oregon Green fluorescent dyes, which bind intracellular proteins to allow up to four cells to be interrogated in a single test well. Sixteen 3-cell screen panels and ten 11-cell identification panels were tested using sera with known antibody specificity. Antibody binding was detected using secondary anti-immunoglobulin G and anti-immunoglobulin M fluorescently labelled antibodies.

RESULTS

Intracellular dyes allowed clear separation of the different screen and identification panel test cells. Three distinct populations of V450+, Oregon Green+ and negative for both stains were demonstrated in the screening panel and an additional double positive for V450 and Oregon Green was utilized to include a fourth cell in the identification panel testing to increase throughput. A total of 158 screen or identification panel RBC/serum combinations were tested against different known antibodies, and expected results were obtained with 100% concordance.

CONCLUSION

This study demonstrates the successful development of a high-throughput multiplexed flow cytometry-based red cell antibody screen and identification panel assays. This method could be implemented in clinical laboratories to complement existing antibody detection methods. The multiplexing enabled via intracellular staining could be utilized to further augment other flow cytometry-based transfusion assays.

A report on a modified protocol for flow cytometry-based assessment of blood group erythrocyte antigens potentially suitable for analysis of weak ABO subgroups

BACKGROUND

Flow cytometry (FC) has proven its utility in scrutinizing AB antigen expression in red blood cells (RBCs), cooperating with serological tests for accurate blood group typing. However, technical difficulties may impair the characterization of weak ABO subtypes when background noises appear at non-negligible levels.

STUDY DESIGN AND METHODS

We sought to establish an FC method that could prevent antibody-induced hemagglutination and an increase in cellular autofluorescence, two major issues inherent to RBC-FC analysis of AB expression. We optimized fixatives, multicolor-staining protocols, and sequential gating strategies. Blood samples from weak ABO subtype cases, B_m and A_el , were analyzed with the established protocol.

RESULTS

The optimized mixture of glutaraldehyde and formaldehyde successfully generated fixed RBCs resistant to agglutination while maintaining low autofluorescence. These features allowed co-staining of leukocyte- and erythrocyte-markers, which enabled sequential gating strategies facilitating the precise AB antigen analysis in purely single RBCs with minimum background noises. By the established FC analysis, we could detect in the B_m sample a small RBC population exhibiting weak B antigen expression. The assay also proved it feasible to identify a small population (0.04%) of RBCs weakly expressing the A antigen in the A_el sample confirmed as harboring a rare c.816dupG ABO variant allele.

CONCLUSION

The RBC-FC analysis described here allows the detection of AB antigens weakly expressed in RBCs while achieving minimum background noise levels in negative control samples. Overall, the modified protocol provides a quick and reliable assay valuable in transfusion medicine and is potentially applicable to the characterization of rare weak ABO variants.

Validation of a flow-cytometry-based red blood cell antigen phenotyping method

BACKGROUND AND OBJECTIVES

Current manual and automated phenotyping methods are based on visual detection of the antigen-antibody interaction. This approach has several limitations including the use of large volumes of patient and reagent red blood cells (RBCs) and antisera to produce a visually detectable reaction. We sought to determine whether the flow cytometry could be developed and validated to perform RBC phenotyping to enable a high-throughput method of phenotyping using comparatively miniscule reagent volumes via fluorescence-based detection of antibody binding.

MATERIALS AND METHODS

RBC phenotyping by flow cytometry was performed using monoclonal direct typing antisera (human IgM): anti-C, -E, -c, -e, -K, -Jk^a , -Jk^b and indirect typing antisera (human IgG): anti-k, -Fy^a , -Fy^b , -S, -s that are commercially available and currently utilized in our blood transfusion services (BTS) for agglutination-based phenotyping assays.

RESULTS

Seventy samples were tested using both flow-cytometry-based-phenotyping and a manual tube standard agglutination assay. For all the antigens tested, 100% concordance was achieved. The flow-cytometry-based method used minimal reagent volume (0.5-1 μl per antigen) compared with the volumes required for manual tube standard agglutination (50 μl per antigen) CONCLUSION: This study demonstrates the successful validation of flow-cytometry-based RBC phenotyping. Flow cytometry offers many benefits compared to common conventional RBC phenotyping methods including high degrees of automation, quantitative assessment with automated interpretation of results and extremely low volumes of reagents. This method could be used for high-throughput, low-cost phenotyping for both blood suppliers and hospital BTS.

Enumeration of Fetal Red Blood Cells, Hemoglobin-Specific RBC Cells, and F Reticulocytes in Human Blood

Recent advances in analytical cytometry have improved diagnostic tools for the study of erythropoiesis in anemic patients and resolution of differential diagnosis in diseases of the erythron. This article presents three applications of red blood cell (RBC) analysis-quantitation of fetal red cells, F-cell enumeration, and F-reticulocyte analysis-which improve diagnostic precision, sensitivity, and specificity, and provide better laboratory indicators of therapeutic efficacy in a variety of hematologic and obstetric disorders. Such advances also include the measurement and quantitation of RBC hemoglobins and their relative ribonucleic acid levels. These advances not only promise to improve diagnostic accuracy and laboratory precision over techniques such as the traditional manual reticulocyte counting method and the Kleihauer-Betke stain method for evaluating fetomaternal hemorrhage (FMH), but also serve as tools for newer assays of anemia diagnosis and improved clinical outcomes. In addition to the primary methods, supporting techniques for preparing spiked controls, automating data analysis, setting up a fetal hemoglobin acquisition protocol, and assaying reticulocytes using thiazole orange are also presented. © 2019 by John Wiley & Sons, Inc.

The prevalence of an elevated F cell population in a maternal and gynaecology cohort

OBJECTIVES

This study aimed to determine F cell prevalence in a cohort of maternal and gynaecology specimens using QuikQuant anti-HbF flow cytometry (FC) kit and to investigate if the presence of maternal F cells can lead to fetomaternal haemorrhage (FMH) overestimation.

BACKGROUND

The gold standard to estimate FMH is the Kleihauer-Betke test (KBT). The KBT has proved to be insufficiently sensitive to detect low numbers of circulating fetal cells due to the presence of maternal F cells. At present, the prevalence of false positive KBT results due to raised maternal F cell population, defined as >5%, is poorly characterised.

METHODS

A total of 120 specimens were tested for the presence of F cells and fetal cells by KBT and anti-HbF FC. The results calculated were compared to determine FMH overestimation.

RESULTS

Of our cohort, 32% showed an elevated F cell population, of which 69% (27 of 39) were clinically significant according to KBT (>2 mL FMH). The mean FMH volumes by KBT and anti-HbF FC were 3·90 mL (0·20-35·40 mL) and 4·09 mL (0·20-9·70 mL), respectively.

CONCLUSION

The study highlighted that an elevated F cell level could be found in the cohort tested, with an F cell level of >10% causing significant FMH overestimation by KBT.