Multicenter evaluation of light transmission platelet aggregation reagents: communication from the ISTH SSC Subcommittee on Platelet Physiology.

BACKGROUND: Light transmission aggregation (LTA) is used widely by the clinical and research communities. Although it is a gold standard, there is a lack of interlaboratory harmonization. OBJECTIVES: The primary objective was to assess whether sources of activators (mainly adenosine diphosphate [ADP], collagen, arachidonic acid, epinephrine, and thrombin receptor activating peptide6) and ristocetin contribute to poor LTA reproducibility. The secondary objective was to evaluate interindividual variability of results to appreciate the distribution of normal values and consequently better interpret pathologic results. METHODS: An international multicenter study involving 28 laboratories in which we compared LTA results obtained with center-specific activators and a comparator that we supplied. RESULTS: We report variability in the potency (P) of activators in comparison with the comparator. Thrombin receptor activating peptide 6 (P, 1.32-2.68), arachidonic acid (P, 0.87-1.43), and epinephrine (P, 0.97-1.34) showed the greatest variability. ADP (P, 1.04-1.20) and ristocetin (P, 0.98-1.07) were the most consistent. The data highlighted clear interindividual variability, notably for ADP and epinephrine. Four profiles of responses were observed with ADP from high-responders, intermediate-responders, and low-responders. A fifth profile corresponding to nonresponders (5% of the individuals) was observed with epinephrine. CONCLUSION: Based on these data, the establishment and adoption of simple standardization principles should mitigate variability due to activator sources. The observation of huge interindividual variability for certain concentrations of activators should lead to a cautious interpretation before reporting a result as abnormal. Confidence can be taken from the fact that difference between sources is not exacerbated in patients treated with antiplatelet agents.

Plasma Isoagglutinin Depletion for Blood Group Independent Plasma Transfusion.

Background: Plasma transfusion is one of the basic treatments in patients with major blood loss. The anti-A and anti-B antibodies contained in the plasma demand ABO blood group compatibility. This is limiting the use of plasma in emergency situations and can cause a shortage in the supply of plasma of certain blood groups. We developed a method for anti-A and anti-B depletion by adsorbing plasma isoagglutinins using red blood cells. Materials and Methods: Three units of fresh frozen plasma were thawed after quarantine storage, pooled, and an aliquot of red cell concentrate was added. After 2 h of incubation at room temperature antibody-red-cell complexes were removed by centrifugation, the isoagglutinin-depleted plasma was split into three units and deep frozen. Isoagglutinin titers, free hemoglobin, residual red cells, clotting factor activity, and sterility of plasma units were determined after isoagglutinin depletion and a double freeze-thawing procedure. Results: Anti-B titers in group A plasma were reduced from values of 1:64 to 1:1 or lower, anti-A titers in group B plasma decreased from values of 1:128 to at least 1:16. Postprocedure clotting factor activities were preserved with 88.0 ± 7.3% (factor V), 106.9 ± 11.4% (factor VIII), and 84.0 ± 7.5% (factor XI) fulfilling the quality control requirements. No residual red cells were found, but free hemoglobin slightly increased to 53.7 ± 5.2 µmol/L. All units were sterile. Discussion: We described a method for the production of anti-A- and anti-B-depleted plasma in a closed system that uses standard equipment. The resulting isoagglutinin-depleted plasma may allow for blood group independent plasma transfusion.

Effect of Methylene Blue Pathogen Inactivation on the Integrity of Immunoglobulin M and G.

INTRODUCTION: In the light of the ongoing SARS-CoV-2 pandemic, convalescent plasma is a treatment option for CO-VID-19. In contrast to usual therapeutic plasma, the therapeutic agents of convalescent plasma do not represent clotting factor activities, but immunoglobulins. Quarantine storage of convalescent plasma as a measure to reduce the risk of pathogen transmission is not feasible. Therefore, pathogen inactivation (e.g., Theraflex®-MB, Macopharma, Mouvaux, France) is an attractive option. Data on the impact of pathogen inactivation by methylene blue (MB) treatment on antibody integrity are sparse. METHODS: Antigen-specific binding capacity was tested before and after MB treatment of plasma (n = 10). IgG and IgM isoagglutinin titers were tested by agglutination in increasing dilutions. Furthermore, the binding of anti-EBV and anti-tetanus toxin IgG to their specific antigens was assessed by ELISA, and IgG binding to Fc receptors was assessed by flow cytometry using THP-1 cells expressing FcRI and FcRII. RESULTS: There was no significant difference in the isoagglutinin titers, the antigen binding capacity of anti-EBV and anti-tetanus toxin IgG, as well as the Fc receptor binding capacity before and after MB treatment of plasma. CONCLUSION: MB treatment of plasma does not inhibit the binding capacity of IgM and IgG to their epitopes, or the Fc receptor interaction of IgG. Based on these results, MB treatment of convalescent plasma is appropriate to reduce the risk of pathogen transmission if quarantine storage is omitted.