The effect of near-infrared low-level light on the in vitro quality of platelets during storage.

BACKGROUND AND OBJECTIVES: Near-infrared (NIR) light has been successfully applied to improve the quality of mouse platelets during storage. Because it is suspected that the mitochondria contain the primary photon acceptor, we hypothesized that human platelets for transfusion may be affected similarly and could benefit from NIR light treatment. MATERIALS AND METHODS: The optimal light dose was determined using portions of platelet concentrates (PCs) in PAS-E. A pool-and-split design was used to prepare PCs in PAS-E or plasma (n = 6). On day 1, one unit of both pairs was illuminated with 830 nm light (light-emitting diodes, 15 J/cm2). PCs were stored at 22°C and sampled regularly for analysis. Data were compared with their corresponding controls with a paired two-sided t-test. RESULTS: Illuminated platelets in PAS-E were less activated with significantly lower CD62P expression (day 8: 10.8 ± 1.8 vs. 12.2 ± 2.6, p < 0.05) and lower Annexin A5 binding (day 8: 11.8 ± 1.9 vs. 13.1 ± 2.4, ns). They produced significantly less lactate resulting in a higher pH (days 6-10). ATP content and mitochondrial membrane potential were not affected. Although these trends were also observed for PCs in plasma, the differences did not reach statistical significance as compared with the control group. CONCLUSION: Our study demonstrates that the glycolysis rate of human platelets can be modulated through the use of NIR, possibly through mitochondrial aerobic metabolism, but this requires confirmation. If NIR illumination can be further optimized, it may potentially become a useful tool in situations in which glycolysis and platelet activation are exacerbated.

Efficacy and safety of platelet additive solution-E stored platelet concentrates.

INTRODUCTION: In 2018, platelet (PLT) additive solution-E (PAS-E) was introduced. The implementation of PAS-E was expected to diminish the number of allergic reactions in recipients following a PLT transfusion. Here, we evaluated the efficacy and safety of transfusions with PLTs stored in PAS-E. STUDY DESIGN AND METHODS: After implementation of PAS-E, data were collected from 2 cohorts of patients with hematological disorders as well as oncology patients, receiving PLTs in PAS-E. A similar patient group in a recent RCT, receiving PLTs in plasma, was used as a historical control group for both cohorts. Endpoints were corrected count increments (CCIs), bleeding scores (only reported in cohort 1), and the incidence of adverse reactions. RESULTS: In cohort 1, the mean 1-h CCI was 14.3 ± 6.9, and the 24-h CCI was 8.7 ± 5.6. In cohort 2, the 1-h CCI was 11.6 ± 7.8 and the 24-h CCI was 7.0 ± 6.1. In the control group, the 1-h CCI was 15.4 ± 5.5 and 24-h CCI 8.7 ± 4.8. Bleeding complications of WHO grade ≥2 occurred in 40% of patients in cohort 1 compared to 44% in plasma PCs. The incidence of adverse reactions was 1.2% in the two PAS-E cohorts, compared to 3.0% in plasma PCs. National hemovigilance data showed a significant reduction in allergic reactions with PAS-E PC transfusions as compared to plasma PCs with an odds ratio of 0.46 (CI 95% 0.37-0.58). CONCLUSION: The CCIs of PLTs in PAS-E were decreased compared to plasma PCs, but clinically acceptable. Allergic transfusion reactions were decreased in PAS-E PCs compared to plasma PCs.

Allogeneic Serum Eye Drops: A Randomized Clinical Trial to Evaluate the Clinical Effectiveness of Two Drop Sizes.

INTRODUCTION: Allogeneic serum from blood donors is starting to be used to treat patients with dry eye disease (DED). However, the optimal dose is not known. We therefore aimed to evaluate the clinical efficaciousness and user-friendliness of micro-sized versus conventional-sized allogeneic serum eye drops (SEDs). METHODS: In a randomized trial, patients with DED first receive micro-sized SEDs (7 µl/unit) for 1 month, followed by a 1-month washout, before receiving conventional-sized SEDs (50 µl/unit) for 1 month; or vice versa. The primary endpoint was the Ocular Surface Disease Index (OSDI) score. Secondary endpoints were tear break-up time (TBT), tear production (TP), and presence of corneal punctate lesions (CP). The user-friendliness of both application systems was also compared. A linear mixed model for cross-over design was applied to compare both treatments. RESULTS: Forty-nine patients completed the trial. The mean OSDI score significantly improved from 52 ± 3 to 41 ± 3 for micro-sized SEDs, and from 54 ± 3 to 45 ± 3 for conventional-sized SEDs. Non-inferiority (margin = 6) of micro-sized SEDs was established. We demonstrate a significant improvement for TBT in case of conventional-sized SEDs and for CP in both treatment groups. TP trended towards an improvement in both treatment groups. The user-friendliness of the conventional drop system was significantly higher. CONCLUSIONS: For the first time, non-inferiority of micro-sized allogeneic SEDs was established. The beneficial effect of both SED volumes was similar as measured by the OSDI score. Although user-friendliness of the micro drop system was significantly lower, it is an attractive alternative as it saves valuable donor serum. TRIAL REGISTRATION: ClinicalTrials.gov (NCT03539159).

Donor variation in stored platelets: Higher metabolic rates of platelets are associated with mean platelet volume, activation and donor health.

BACKGROUND: Platelets (PLTs) differ in glycolytic activity, resulting in rapid acidification of 'poor' storing PLT concentrates (PCs) in plasma, or depletion of glucose when stored in PLT additive solution (PAS). We aimed to understand why PLT glycolysis rates vary between donors and how this affects storage performance. STUDY DESIGN AND METHODS: Buffy coats from donors <45, 45-70 and >70 years were selected and single-donor PCs in plasma or PAS-E were prepared. PCs were stored for 8 days at 22 ± 2°C and sampled regularly for analysis. Mitochondrial activity was analyzed with an Oroboros oxygraph. Age groups, or subgroups divided into quartiles based on glucose consumption, were analyzed with ANOVA. RESULTS: In each comparison, PCs of the different groups were not different in volume and cellular composition. PLTs with the highest glucose consumption had a higher initial mean platelet volume (MPV) and developed higher CD62P expression and Annexin A5 binding during storage. Higher glycolytic activity in these PLTs was not a compensation for lower mitochondrial ATP production, because mitochondrial ATP-linked respiration of fresh PLTs correlated positively with MPV (R2  = 0.71). Donors of high glucose-consuming PLTs had more health-related issues. Storage properties of PCs from donors over 70 were not significantly different compared to PCs from donors younger than 45 years. CONCLUSIONS: High glucose-consuming PCs developing higher activation levels, not only displayed enhanced mitochondrial activity but were also found to contain larger PLTs, as determined by MPV. Storage performance of PLTs was found to be associated with donor health, but not with donor age.

Altered Fc glycosylation of anti-HLA alloantibodies in hemato-oncological patients receiving platelet transfusions.

BACKGROUND: The formation of alloantibodies directed against class I human leukocyte antigens (HLA) continues to be a clinically challenging complication after platelet transfusions, which can lead to platelet refractoriness (PR) and occurs in approximately 5%-15% of patients with chronic platelet support. Interestingly, anti-HLA IgG levels in alloimmunized patients do not seem to predict PR, suggesting functional or qualitative differences among anti-HLA IgG. The binding of these alloantibodies to donor platelets can result in rapid clearance after transfusion, presumably via FcγR-mediated phagocytosis and/or complement activation, which both are affected by the IgG-Fc glycosylation. OBJECTIVES: To characterize the Fc glycosylation profile of anti-HLA class I antibodies formed after platelet transfusion and to investigate its effect on clinical outcome. PATIENTS/METHODS: We screened and captured anti-HLA class I antibodies (anti-HLA A2, anti-HLA A24, and anti-HLA B7) developed after platelet transfusions in hemato-oncology patients, who were included in the PREPAReS Trial. Using liquid chromatography-mass spectrometry, we analyzed the glycosylation profiles of total and anti-HLA IgG1 developed over time. Subsequently, the glycosylation data was linked to the patients' clinical information and posttransfusion increments. RESULTS: The glycosylation profile of anti-HLA antibodies was highly variable between patients. In general, Fc galactosylation and sialylation levels were elevated compared to total plasma IgG, which correlated negatively with the platelet count increment. Furthermore, high levels of afucosylation were observed for two patients. CONCLUSIONS: These differences in composition of anti-HLA Fc-glycosylation profiles could potentially explain the variation in clinical severity between patients.

The history of buffy coat platelet concentrates: The Dutch story.

The buffy coat method as a source for platelet concentrates was developed in the 1970s and is still used in many blood centres around the world. Development of the method sparked various technological advances in blood collection, processing and storage. At the time, the need for platelet concentrates sharply increased because of better treatment regimens for (onco)haematological diseases, which forced blood centres to standardize and automate their production processes as much as the technology would allow. In this review, a historical overview of the Dutch experiences is provided in the context of the international developments.

Allogeneic and autologous serum eye drops: a pilot double-blind randomized crossover trial.

PURPOSE: Serum eye drops (SEDs) are used to treat a variety of ocular surface defects. Serum eye drops (SEDs) are normally produced from the patient's blood. However, not all patients can donate sufficient or suitable blood, and logistics can be challenging. Allogeneic blood from voluntary blood donors does not have these disadvantages. Our aim was to evaluate whether autologous and allogeneic SEDs have comparable efficacy and tolerability. METHODS: In a prospective, double-blind crossover trial, patients with severe dry eyes were randomized to first receive autologous SEDs for one month, followed by one-month washout, before receiving allogeneic SEDs for 1 month; or receive the SED preparations in reverse order. The Ocular Surface Disease Index (OSDI) was the primary endpoint, and various secondary endpoints were determined. A linear mixed model with random intercept for each patient was applied per treatment group to compare the pre- and postoutcome measurements. RESULTS: Nineteen patients were enrolled, of whom 15 completed the trial. When autologous SEDs were used, the mean ± SD OSDI improved from 62 ± 19 to 57 ± 18. For allogeneic SEDs, the OSDI changed from 59 ± 20 to 56 ± 23. The estimated mean difference (95% confidence interval) was -4.2 (-9.5 to 1.2) for autologous and -4.5 (-9.8 to 0.9) for allogeneic SEDs (both, not significant). Adverse events were mild and resolved completely. CONCLUSION: Autologous and allogeneic SEDs have comparable efficacy and tolerability for use in patients with severe dry eyes. Allogeneic SEDs are therefore an attractive alternative for patients who need SEDs but are clinically or logistically unable to donate blood.

Exploring the components of bleeding outcomes in transfusion trials for patients with hematologic malignancy.

Clinically significant bleeding in patients with hematologic malignancies is a heterogeneous composite outcome currently defined as World Health Organization (WHO) bleeding Grades 2, 3, and 4. However, the clinical significance of some minor bleeds categorized as WHO Grades 1 and 2 remains controversial. We analyzed the number and frequency of individual signs and symptoms of WHO Grades 1 and 2 bleeds and explored their association with more severe incident bleeds graded as WHO Grades 3 and 4. STUDY DESIGN AND METHODS: We aggregated daily bleeding assessment data from three randomized controlled trials conducted in patients with hematologic malignancies that used bleeding as an outcome. Cox proportional hazard regression analysis was used to identify signs and symptoms categorized as WHO Grades 1 and 2 bleeds that were associated with more severe bleeds (Grades 3 and 4). RESULTS: We collected data from 315 patients (n = 5476 daily bleeding assessments; 3383 [61.8%] with a bleed documented). A total of 98.3% (3326/3383) were Grade 1 and 2 bleeds and 1.7% (57/3383) were Grades 3 and 4. Grade 1 and 2 bleeds were composed of 20 different bleeding signs and symptoms. Hematuria (hazard ratio, 16.1; 95% confidence interval, 4.4-59.2; P < .0001) was associated with incident Grade 3 or 4 bleeds. CONCLUSION: In patients with hematologic malignancy, only hematuria (microscopic and/or macroscopic) was associated with more severe incident bleeds. This findings require validation in independent data sets.

Quality of Platelets in Stored Whole Blood.

Transfusion of whole blood rather than blood components is gaining popularity. It is easy to use, with one transfusion product to administer rather than 3, and is held at one storage temperature. It only contains anticoagulant-preservative solution, while components contain various storage solutions, which in theory may induce dilution coagulopathy. In this review, the quality of platelets in stored whole blood is summarized. In cold-stored whole blood, the platelet count declines by 1% to 2% per day. The responsiveness to various agonists declines during the storage time, but this appears to have a limited impact on clotting time or on clot strength as measured with thromboelastography. Animal studies have confirmed that platelets from stored whole blood participate equally well in clot formation. The recovery of platelets in stored whole blood is acceptable during at least 15 days of storage. The survival of platelets after transfusion is only 1 day, but this is likely to be sufficient for the intended patient group requiring massive transfusions, as the platelets are rapidly consumed in the wound area. In addition to the logistic benefits, there are drawbacks, most importantly having a sufficiently large inventory with an acceptable outdating rate, particularly since massive transfusions are rare, while requiring a lot of whole blood. The positive experience of the United States military with whole blood transfusion is often brought forward for introduction in the civilian blood bank, but patients with trauma are only a small fraction of the civilian population requiring massive transfusions. It needs to be determined whether in the resourceful environment of the hospital, these patients benefit from whole blood transfusions. Optimization of whole blood storage, with focus on platelet quality, needs to be performed to allow extension of the storage time beyond 15 days to a point where the number of units in inventory and outdating can be balanced.

Revisiting study design and methodology for pathogen reduced platelet transfusions: a round table discussion.

Pathogen inactivation/reduction technologies for platelet components have been developed to enhance microbial safety, and many studies have been carried out to determine whether this technique adversely affects the platelet's ability to stop or prevent bleeding. These clinical trials require inclusion of several hundred patients, are costly, and take many years to complete. To address these challenges, a meeting was organized consisting of two expert presentations followed by a roundtable discussion focused on possible new approaches to evaluate the clinical efficacy of pathogen-reduced platelets. The value of laboratory measures to provide information on platelet count after transfusion or to serve as a surrogate for bleeding risk was discussed. Also, other types of trial designs (cluster trials, stepped wedge designs, and Phase 4 postmarketing surveillance studies) as well as a clinically meaningful standardized safety endpoint to evaluate pathogen- reduced platelets were also discussed.

The association between haemorrhage and markers of endothelial insufficiency and inflammation in patients with hypoproliferative thrombocytopenia: a cohort study.

In daily haematological practice, predicting bleeding in thrombocytopenic patients is difficult, and clinicians adhere to transfusion triggers to guide patients through the aplastic phase of chemotherapy. Platelet count is not the only determinant of bleeding and additional mechanisms for impending haemostasis are likely. Beside clot formation, platelets are essential for the maintenance of integrity of vascular beds. We therefore prospectively investigated associations between biomarkers for endothelial damage (urine albumin excretion) and inflammation (C-reactive protein) and bleeding (WHO grading) in 88 patients with 116 on-protocol episodes. We found an increase in grade 2 bleeding with a higher urine albumin/creatinine ratio one day after the measurement [odds ratio (OR) 1·24 for every doubling of the ratio, 95% CI 1·05-1·46, P-value 0·01] and a 29% increase in the odds of grade 2 bleeding for every doubling of serum C-reactive protein (CRP) (95% CI 1·04-1·60, P-value 0·02) after correction for morning platelet count. The 24 h post-transfusion corrected count increment (CCI24 ) showed a significant association with these biomarkers: increasing urine albumin/creatinine ratio and CRP were associated with lower CCI24. We report two inexpensive and easy-to-apply biomarkers that could be useful in designing a prediction model for bleeding risk in thrombocytopenic patients.

Effect of storage of platelet concentrates in PAS-B, PAS-C, or plasma on transfusion reactions.

BACKGROUND: Reports on the clinical consequences of longer storage time of platelet concentrates are contradictory. The objective of this study was to assess whether longer storage times are associated with a higher risk of transfusion reactions. STUDY DESIGN AND METHODS: We gathered storage times of pooled platelet concentrates related to transfusion reactions reported to the national hemovigilance office from 2004 to 2015. These were combined with storage times of platelet concentrates in the reference population to compare incidences of transfusion-associated circulatory overload, transfusion-related acute lung injury, allergic reactions, febrile nonhemolytic reactions, and "other" reactions between storage time categories. RESULTS: A total of 567,053 platelet concentrates and 1870 transfusion reactions were analyzed. Among platelet additive solution (PAS)-B platelet recipients, the odds ratio of a storage time of 4 to 5 days compared to 1 to 3 days was 1.60 (95% confidence interval [CI], 1.17-2.18) for allergic, and 1.47 (1.09-1.98) for febrile reactions. For PAS-C platelet recipients, the odds ratio for allergic reactions was 3.78 (95% CI, 1.31-10.9) for 4 to 5 days, and 4.57 (95% CI, 1.57-13.4) for 6- to 7-day-old platelets when compared to 1- to 3-day-old units. In all other studied reaction types, no statistically significant association was observed in platelets in plasma, PAS-B, and PAS-C. CONCLUSIONS: In plasma platelets, longer storage time was not associated with a higher incidence of transfusion reactions. In PAS platelets, longer storage time was associated with higher transfusion reaction incidences, in particular for allergic reactions with both PAS fluids and febrile reactions with PAS-B. This indicates that the effect of storage time is different for different reaction types and depends on the storage fluid.

Thromboelastography as a tool to evaluate blood of healthy volunteers and blood component quality: a review.

Thromboelastography is a technique to evaluate the overall coagulation behaviour of blood and blood components. First, we evaluated the literature concerning the use of thromboelastography for characterizing coagulation behaviour of healthy volunteers, such as blood donors. Overall coagulation is sensitive to gender, most likely caused by the difference in haematocrit and plasma content of male versus female blood. Smaller and less pronounced effects in thromboelastographic response are caused by differences in fibrinogen level or by use of oral contraceptives. Short-term hypercoagulable effects are observed after smoking or blood donation, while small effects of non-steroidal anti-inflammatory drugs on platelets are also present. Second, in whole blood donations, the thromboelastographic variables are also sensitive to storage time and temperature, but are less sensitive to levels of clotting factors. Platelet count and quality have little influence on thromboelastographic variables, and differences are mainly observed at counts <100x109 /l, after extended storage time of platelet concentrates or storage under specific conditions, including freezing. Thromboelastographic profiles of plasma samples are mainly affected by residual cell counts, microparticles and fibrinogen levels, and less by levels of clotting factors. Taken together, publications have shown that as an overall clotting test, thromboelastography may support optimization of blood component preparation and storage with regard to temperature, time and secondary and tertiary treatments. Minimal deviations of in vitro quality are most reliable demonstrated when an appropriate assay is chosen.

A comprehensive proteomics study on platelet concentrates: Platelet proteome, storage time and Mirasol pathogen reduction technology.

Platelet concentrates (PCs) represent a blood transfusion product with a major concern for safety as their storage temperature (20-24°C) allows bacterial growth, and their maximum storage time period (less than a week) precludes complete microbiological testing. Pathogen inactivation technologies (PITs) provide an additional layer of safety to the blood transfusion products from known and unknown pathogens such as bacteria, viruses, and parasites. In this context, PITs, such as Mirasol Pathogen Reduction Technology (PRT), have been developed and are implemented in many countries. However, several studies have shown in vitro that Mirasol PRT induces a certain level of platelet shape change, hyperactivation, basal degranulation, and increased oxidative damage during storage. It has been suggested that Mirasol PRT might accelerate what has been described as the platelet storage lesion (PSL), but supportive molecular signatures have not been obtained. We aimed at dissecting the influence of both variables, that is, Mirasol PRT and storage time, at the proteome level. We present comprehensive proteomics data analysis of Control PCs and PCs treated with Mirasol PRT at storage days 1, 2, 6, and 8. Our workflow was set to perform proteomics analysis using a gel-free and label-free quantification (LFQ) approach. Semi-quantification was based on LFQ signal intensities of identified proteins using MaxQuant/Perseus software platform. Data are available via ProteomeXchange with identifier PXD008119. We identified marginal differences between Mirasol PRT and Control PCs during storage. However, those significant changes at the proteome level were specifically related to the functional aspects previously described to affect platelets upon Mirasol PRT. In addition, the effect of Mirasol PRT on the platelet proteome appeared not to be exclusively due to an accelerated or enhanced PSL. In summary, semi-quantitative proteomics allows to discern between proteome changes due to Mirasol PRT or PSL, and proves to be a methodology suitable to phenotype platelets in an unbiased manner, in various physiological contexts.

The role of pathogen-reduced platelet transfusions on HLA alloimmunization in hemato-oncological patients.

BACKGROUND: Platelet transfusions can induce alloimmunization against HLA antigens. The use of pathogen-reduced platelet concentrates (PCs) was suggested to reduce HLA alloimmunization and concomitant transfusion refractoriness. METHODS: This study investigated HLA alloimmunization in available samples from 448 hemato-oncological patients who were randomized for the Pathogen Reduction Evaluation and Predictive Analytical Rating Score (PREPAReS) trial to receive either untreated or pathogen-reduced PCs (Mirasol, Terumo BCT Inc.). Anti-HLA Class I and II antibodies were determined before the first platelet transfusion and weekly thereafter using multiplex assay with standard cutoffs to detect low- as well as high-level antibodies. RESULTS: When using the lower cutoff, in patients who were antibody negative at enrollment, 5.4% (n = 12) developed anti-HLA Class I antibodies after receiving untreated PCs, while this was significantly higher in patients receiving pathogen-reduced PCs, 12.8% (n = 29; p = 0.009, intention-to-treat [ITT] analysis). A similar but nonsignificant trend was observed in the per-protocol (PP) analysis (5.4% vs. 10.1%; p = 0.15). HLA class II antibody formation was similar between both types of PCs in the ITT analysis, while the PP analysis showed a trend toward lower immunization after receiving pathogen-reduced PCs. Multivariate analysis identified receiving pathogen-reduced platelets as an independent risk factor for HLA Class I alloimmunization (ITT: odds ratio [95% confidence interval] = 3.02 [1.42-6.51], PP: odds ratio [95% confidence interval] = 2.77 [1.00-5.40]), without affecting HLA Class II alloimmunization. When using the high cutoff value, the difference in HLA Class I alloimmunization between study arms remained significant in the ITT analysis and again was not significant in the PP analysis. CONCLUSION: Our data clearly indicate that Mirasol pathogen inactivation does not prevent HLA Class I or II alloimmunization after platelet transfusions.

Platelet storage properties are associated with donor age: in vitro quality of platelets from young donors and older donors with and without Type 2 diabetes.

BACKGROUND AND OBJECTIVES: Previously it has been shown that platelet (PLT) storage performance is consistent by donor. Differences involved metabolic activity, which might be caused by mitochondrial (dys)function, associated with age and age-related diseases like Type 2 diabetes (T2D). We aimed to test PLTs from young donors in comparison with PLTs from older donors with or without diagnosis for T2D. MATERIALS AND METHODS: Fifteen whole blood donors <30 year were selected, and single-donor platelet concentrates (sPC) were prepared from buffy coats (BC) and plasma. Also, 2 × 11 sPC were prepared from matched donors >45 years with and without T2D. The sPC were stored for 8 days and analysed at regular intervals for in vitro quality. RESULTS: Donors were 24 ± 3, 60 ± 7 (without T2D) and 59 ± 8 (with T2D) years old. All sPC groups had comparable volume and PLT content. On Day 8, sPC from young donors showed higher pH37°C than sPC from older donors (6.84 ± 0.15 vs. 6.40 ± 0.48, P < 0.01), due to lower lactate production. Also, CD62P expression (22.9 ± 7.4 vs. 48.8 ± 24.0%, P < 0.01) and HSR reflected better in vitro quality. PLT storage properties of sPC obtained from T2D donors (pH = 6.51 ± 0.35) were not different from sPC of matched donors (pH = 6.40 ± 0.48). No differences in mitochondrial membrane potential were detected between the groups. CONCLUSION: Platelets from young donors exhibited the best storage conditions. On average, PLTs from older donors showed poorer in vitro quality but, considering the sub-optimal storage conditions, the implications for the daily blood bank routine is probably small. No association with T2D was found.

The quality of platelet concentrates related to corrected count increment: linking in vitro to in vivo.

BACKGROUND: Storage of platelet concentrates (PCs) results in reduced recovery and survival of transfused platelets (PLTs). Upon storage PLTs develop storage lesion that can be monitored by several laboratory tests. However, correlation of these descriptive tests with corrected count increments (CCIs), a marker frequently used to establish the effectiveness of PLT transfusions, is limited or unknown. This study investigated to what extent a functional test or a combined in vitro rating score improves the correlation of laboratory tests with 1-hour CCI. STUDY DESIGN AND METHODS: PCs were analyzed using six different laboratory tests (n = 123) before transfusion in a prophylactic setting to 74 hematooncologic patients. Linear regression and Spearman correlation were used to determine associations between descriptive (either separately or combined in an in vitro rating score) or functional test results and 1-hour CCIs obtained after transfusion. RESULTS: CD62P expression (r = -0.45), annexin V binding (r = -0.36), the updated in vitro rating score (r = 0.50), and PLT responsiveness after thrombin receptor activator for peptide-6 (TRAP) (r = 0.43-0.57) or adenosine diphosphate stimulation (r = 0.11-0.51) significantly correlated to 1-hour CCIs obtained after transfusion, whereas lactate concentration, ThromboLUX score, and thromboelastography measurements did not. The strongest correlations were observed for in vitro rating score and PLT responsiveness after TRAP stimulation and these tests could explain 24 and 33% of the observed variation in 1-hour CCI, respectively. CONCLUSION: Combining descriptive markers in one in vitro rating score improved correlation to 1-hour CCI compared to the tests separately. Of all tests investigated, mean PLT responsiveness after TRAP stimulation showed the strongest clinical correlation and was best able to predict the 1-hour CCI.