丹参酮ⅡA抑制血小板与肿瘤细胞相互作用的实验研究

目的 探究丹参酮IIA(TanⅡA)抗血小板作用以及抑制人血小板与结肠癌HCT116细胞的相互作用。方法 采用不同浓度TanⅡA(10、20、40μmol/L)处理健康志愿者全血或血小板,通过血栓弹力图试验（TEG）检测二磷酸腺苷（Adenosinediphosphate,ADP）、花生四烯酸（arachidonicacid,AA）抑制率,流式细胞术检测血小板CD62P、PAC-1表达率,黏附试验检测TanⅡA处理后血小板与HCT116细胞的黏附情况,划痕试验检测TanⅡA处理后血小板对HCT116细胞的迁移能力的影响。结果 TEG结果表明,TanIIA呈浓度依赖性抑制ADP、AA诱导的血小板聚集（P <0.01）,低浓度TanⅡA处理就能获得较好的ADP抑制率,为（73.48±19.63）%,高浓度TanⅡA才能获得较好的AA抑制率,为（78.20±18.58）%。流式细胞术结果显示,TanⅡA可以呈浓度依赖抑制凝血酶或ADP诱导的血小板表面CD62P、PAC-1表达（P <0.05）。黏附试验结果证实,TanⅡA能显著抑制凝血酶或ADP激活血小板与HCT116细胞之间的...     

血栓弹力图在冠心病患者抗血小板治疗中的临床应用

目的在冠心病患者中,使用血栓弹力图测定血小板抑制率,评价抗血小板药物的作用效果。方法对该院联合服用阿司匹林和氯吡格雷的402例冠心病住院患者进行血栓弹力图检测,测得二磷酸腺苷(ADP)受体途径诱导的血小板抑制率和花生四烯酸(AA)通路途径诱导的血小板抑制率,按照ADP和AA抑制率参考值高低分别分为低、正常、高抑制率3组,并对各组的普通杯R、K、角度、MA值相关性进行统计分析。结果 ADP低、正常、高抑制率3组为81例(20.1%)、251例(62.4%)和70例(17.4%),AA低、正常、高抑制率3组为50例(12.4%)、174例(43.3%)、178例(44.3%)。按照ADP低、正常、高抑制率分组,3组间的R、K、角度、MA值、AA低、正常、高抑制率差异均无统计学意义(P0.05),按照AA低、正常、高抑制率分组,ADP抑制率在正常抑制率组与高抑制率组比较差异有统计学意义(P0.05)。结论普通杯参数不能反映阿司匹林和氯吡格雷抗血小板的效果,ADP抑制率与AA抑制率存在一定的正相关性,根据AA和ADP抑制率的情况发现对阿司匹林和氯吡格雷抵抗的患者,进而调整用药方案。     

动脉粥样硬化高危人群中阿司匹林抵抗调查

目的调查社区动脉粥样硬化高危人群中阿司匹林抵抗(AR)或半抵抗(ASR)的发生率及其流行病学特征,并探讨其与动脉粥样硬化危险因素的相关性。方法筛选200例动脉粥样硬化高危患者服用阿司匹林(100 mg/d)至少7 d以上,用二磷酸腺苷(ADP)和花生四烯酸(AA)诱导剂测定其前后血小板聚集功能变化及血清血栓烷B2(TXB2)水平测定。结果 200例动脉粥样硬化高危人群中AR发生率为4.5%,ASR者占20.7%。血清TXB2水平,AA、ADP诱导的血小板聚集率与健康对照组相比差异有统计学意义(P<0.01);血清TXB2水平与血小板聚集率有较好的相关性(γ=0.871)。结论社区动脉粥样硬化高危人群服用阿司匹林后部分患者产生AR或ASR;检测AA、ADP诱导的血小板聚集率,血清TXB2水平可作为动脉粥样硬化高危人群发生AR或ASR的评价指标。     

冠心病患者经皮冠状动脉介入治疗术后抗血小板药物治疗监测及平均血小板体积变化

目的比较血栓弹力图(TEG)和光学比浊法(LTA)在监测冠心病患者经皮冠状动脉介入治疗(PCI)术后抗血小板药物中的相关性;观察PCI术后双联抗血小板治疗患者平均血小板体积(MPV)变化。方法回顾2013年3月至2014年5月在北京大学第一医院行PCI并接受规范双联抗血小板治疗的患者177例;回顾分析其TEG测定的二磷酸腺苷(ADP)、花生四烯酸(AA)诱导的血小板抑制率,服用抗血小板药物前后MPV,以及其中99例患者LTA测定的血小板聚集率。结果 ADP、ARA诱导的LTA血小板聚集率与TEG血小板抑制率无相关性(P均0.05)。氯吡格雷低反应性LTA和TEG检出率分别为30.3%和45.5%,阿司匹林低反应性检出率分别为19.2%和31.3%,低反应性检出率LTA低于TEG法(P0.05)。177例患者中,氯吡格雷低反应组和敏感组、阿司匹林低反应性组和敏感组服药后MPV均较服药前降低(P均0.01);服药前及服药后氯吡格雷低反应性组MPV均低于敏感组(P均0.05);氯吡格雷及阿司匹林低反应组服药后PLT高于服药前(P均0.05)。结论 TEG和LTA两种方法相关性较差,抗血小板药物低反应检出率均较高,值得临床医生注意;服用双联抗血小板药物后MPV降低;服药后PLT上升患者更易发生药物低反应性;MPV偏低患者氯吡格雷低反应性发生可能性更大。     

血栓弹力图对老年患者抗血小板治疗的研究

目的：应用血栓弹力图观察老年患者服用抗血小板药物后血小板抑制率情况。方法对15例服用阿司匹林和85例服用氯吡格雷的老年患者进行血栓弹力图检测,分别测定花生四烯酸（AA）和二磷酸腺苷（ADP）途径诱导的血小板抑制率。结果服用阿司匹林的患者对血小板的抑制率平均值为67.85%±34.47%,其中有33.3%其AA诱导的血小板聚集率≤50%,提示患者对阿司匹林反应低下。服用氯吡格雷的患者对血小板的抑制率平均值为56.00%±30.04%,其中有21.2%其ADP诱导的血小板聚集率＜30%,提示患者对氯吡格雷反应低下。结论对于接受抗血小板治疗的老年患者,进行血栓弹力图检测是必要的。     

CYP2C19、PON1基因多态性与氯吡格雷在ACS行PCI术后血小板抑制功能的关联分析

目的探讨CYP2C19、PON1基因多态性与氯吡格雷在急性冠脉综合征(ACS)行经皮冠状动脉介入治疗(PCI)术后血小板抑制功能的相关性。方法回顾性分析2016年6月至2017年5月该院ACS行PCI患者636例,按使用抗血小板药物分为氯吡格雷组(491例)和替格瑞洛组(145例)。采用荧光检测仪检测CYP2C19*2、CYP2C19*3、CYP2C19*17、ABCB1、PON1基因;血栓弹力图仪(TEG)检测服药24h后血小板抑制功能,采用t检验和方差分析比较各组血小板抑制率的差异,逻辑回归分析基因型与抗血小板反应性的关联。结果基因型分析显示CYP2C19功能缺失型等位基因*2、*3至少1个单核苷酸多态性(SNP)位点突变率分别为55.6%和7.2%,功能增强型等位基因*17的突变率为0.6%。ABCB1与PON1基因位点突变率基本相同,分别为60.5%和59.4%。TEG检测二磷酸腺苷(ADP)诱导的血小板抑制率:替格瑞洛组较氯吡格雷组高,差异有统计学意义(t=5.75,P0.05),其中比较两组快代谢型ADP抑制率差异无统计学意义(t=1.92,P0.05),而中间代谢型与慢代谢型差异有统计学意义(t=5.06,P0.05;t=2.03,P0.05)。逻辑回归分析患者基本临床信息与替格瑞洛组基因多态性对药物ADP诱导血小板反应性的影响均无统计学意义(P0.05),而氯吡格雷组携带1个CYP2C19功能缺失型等位基因与ABCB1基因对反应性的影响也均无统计学意义(P0.05),携带两个CYP2C19功能缺失型等位基因或至少携带1个PON1突变基因对预测低反应性风险差异有统计学意义(OR:6.622,95%CI:2.283~19.210,P0.05;OR:2.620,95%CI:1.074~6.393,P=0.034;OR:3.503,95%CI:1.104~11.113,P=0.033)。结论对于ACS行PCI的患者,检测CYP2C19功能缺失型等位基因与PON1基因对预测氯吡格雷抗血小板低反应性风险具有重要意义。     

两种药物单独和联合使用对急性脑梗死患者血小板抑制率及超敏C反应蛋白水平的影响

目的研究急性脑梗死患者应用阿司匹林及氯吡格雷抗血小板的临床治疗效果及对血清相关炎症因子水平的影响,为临床抗血小板药物个体化治疗提供参考。方法选取山东省立第三医院2015年1月至2016年12月收治的300例急性脑梗死患者分为阿司匹林组、氯吡格雷组及联合组,每组各100例。治疗前、治疗后2周应用血栓弹力图(TEG)测定花生四烯酸(AA)水平及二磷酸腺苷(ADP)途径诱导的血小板抑制率,采用免疫比浊法测定3组患者血清超敏C反应蛋白(hs-CRP)水平。比较3组患者血小板抑制率、hs-CRP水平、患者神经功能评分及卒中复发率。结果 3组患者治疗后AA水平、ADP途径诱导的血小板抑制率均高于治疗前,差异均有统计学意义(P0.05)。3组之间AA水平及ADP途径诱导的血小板抑制率差异均有统计学意义(P0.05)。3组患者治疗后血清hs-CRP水平较治疗前明显降低,联合组治疗后血清hs-CRP水平明显低于其余两组,差异均有统计学意义(P0.05)。联合组神经功能恢复更佳,卒中复发率更低。结论阿司匹林及氯吡格雷均具有抗血小板作用,但两种药物联合应用可从2个途径有效抑制血小板聚集,起到更强的抗血小板作用,降低血小板聚集活性,减少血管炎性反应,减少血栓复发的风险。     

吸烟对冠心病心绞痛型患者经皮冠状动脉介入治疗术后二联抗血小板疗效的影响

目的观察吸烟对冠心病心绞痛型患者经皮冠状动脉介入治疗(PCI)术后二联抗血小板疗效的影响。方法冠心病心绞痛PCI术后患者493例,均连续服用阿司匹林100mg/d达7d以上,根据病史分为吸烟组241例和非吸烟组252例,入选时所有患者均测定花生四烯酸(AA)和二磷酸腺苷(ADP)诱导的血小板聚集率,后予氯吡格雷300mg负荷量口服,并于服用氯吡格雷75mg/d3d后再次测定ADP诱导的血小板聚集率。结果吸烟组与非吸烟组在性别、红细胞计数、血小板计数、血小板压积和低密度脂蛋白胆固醇等方面无显著性差异(P0.05)。两组阿司匹林抵抗和半抵抗的总发生率为19.1%;吸烟组阿司匹林抵抗和半抵抗的发生率高于非吸烟组(25.5%vs14.3%,P=0.027),年龄(OR=3.79,95%CI:1.77～8.12)和吸烟(OR=1.98,95%CI:1.18～4.43)是阿司匹林抵抗和半抵抗的独立危险因素。两组氯吡格雷抵抗发生率为19.5%,吸烟组氯吡格雷抵抗的发生率低于非吸烟组(13.2%vs24.3%,P=0.03),吸烟是氯吡格雷抵抗的保护因素(OR=0.22,95%CI:0.09～0.54)。结论吸烟降低阿司匹林的抗血小板效应,但增强氯吡格雷的抗血小板效应。     

平均血小板体积在高风险冠状动脉介入治疗患者中对抗血小板治疗低反应的预测价值

目的通过分析行高风险冠状动脉介入治疗(PCI)的患者中,其平均血小板体积(MPV)与抗血小板药物(阿司匹林及氯吡格雷)反应性的关系,以期了解MPV对两种药物治疗低反应的预测价值。方法选取住院治疗的急性冠脉综合征(ACS)且行高风险PCI治疗的患者共74例。所有患者入院时即给予阿司匹林300 mg,氯吡格雷300~600 mg,次日开始予阿司匹林100 mg/d,氯吡格雷75 mg/d的维持治疗。负荷量给药24 h后采用血栓弹力图(TEG)检测阿司匹林及氯吡格雷对血小板的抑制率。以花生四烯酸(AA)诱导的血小板聚集抑制率50%作为阿司匹林低反应的指标,据此将患者分为阿司匹林低反应组(AL)和阿司匹林敏感组(AS),以二磷酸腺苷(ADP)诱导的血小板聚集抑制率30%作为氯吡格雷低反应的指标,将患者分为氯吡格雷低反应组(CL)和氯吡格雷敏感组(CS),分别比较不同药物两组之间临床资料、生化指标、手术相关资料及MPV水平。结果共有27例(36.5%)患者发生CL,21例(28.4%)患者发生AL。CL组的MPV水平显著高于CS组,同样AL组的MPV水平也显著高于AS组(均P0.05)。单因素分析得出MPV增高是AL的独立预测因素。Logistic回归分析得出,CL的发生与MPV增高也有密切关系(OR=4.170,95%CI:1.971~8.823,P0.01)。根据受试者工作特性分析,MPV预测CL、AL的最佳截点分别为9.95 f L和10.65 f L,敏感性为100%和81.0%,特异性为55.3%和37.7%(CL曲线下面积:0.861,95%CI:0.779~0.942,P0.01;AL曲线下面积:0.732,95%CI:0.609~0.856,P=0.002)。结论在高风险PCI的患者中,高MPV水平是CL、AL的独立预测指标。     

血小板活化标志物、维生素D与氯吡格雷抵抗的相关性

目的探讨血小板活化标志物、维生素D与缺血性脑卒中患者抗血小板药物抵抗的相关性。方法 2017年6月至2018年6月,190例接受阿司匹林和氯吡格雷联合治疗的缺血性脑卒中患者,于用药后7～10 d检测二磷酸腺苷(ADP)和花生四烯酸(AA)诱导的最大血小板聚集率(MPAR)、血小板CD_(62p)活化百分率、血浆P选择素和维生素D。根据MPAR将患者分为抗血小板药物抵抗组和敏感组。结果阿司匹林抵抗率为1.2%,氯吡格雷抵抗率24.7%(抵抗组47例,敏感组143例)。抵抗组血小板CD_(62p)活化百分率(t=-5.232, P 0.001)、高血压患病率(χ~2=4.878, P 0.05)均高于敏感组,维生素D浓度明显低于敏感组(t=3.052, P 0.01),两组血浆P选择素浓度无显著性差异(t=-0.684, P=0.253)。Logistic回归分析结果显示,高血压(OR=5.538, 95%CI:1.204～25.470, P 0.05)、血小板CD62P活化百分率(OR=1.082,95%CI:1.041～1.092, P 0.05)是氯吡格雷抵抗的危险因素,而维生素D (OR=0.848, 95%CI:0.755～0.953,P 0.01)是氯吡格雷抵抗的保护因素。结论抑制血小板活化和补充维生素D可能有助于提高氯吡格雷的疗效。     

Endogenous glutathione and platelet function in platelet concentrates stored in plasma or platelet additive solution

Platelet function was studied in platelet concentrates by assay of the thrombin-induced release of endogenous serotonin and presence of the swirling phenomenon in relation to endogenous glutathione (GSH) and cysteine. In platelets stored in plasma, addition of cysteamine resulted in only a moderate fall in GSH after 5 days of storage, from an average of 14.91 to 11.46 nmol per 109 platelets. Exogenously added GSH had no effect, and addition of buthionine sulfoximine (BSO) resulted in almost complete depletion of GSH, to an average of 0.65 nmol per 109 platelets. Addition of cysteamine or GSH resulted in increased endogenous cysteine whereas BSO had no effect. In platelets stored in a platelet additive solution (T-sol), complete depletion of GSH was found in the presence of cysteamine, GSH and BSO. Endogenous serotonin was unchanged during storage both in plasma and in additive solution (2.8 nmol per 109 platelets). Despite almost total depletion of endogenous GSH, the thrombin-induced release of serotonin after 5 days' storage was significantly affected only in the presence of BSO in platelets stored in additive solution (mean values 72.3% vs. 63.3% of endogeneous serotonin, P < 0.05). Similarly, addition of cysteamine or GSH had no significant effect on swirling but BSO reduced the swirling score after 5 days' storage in platelet additive solution compared with plasma. After 10 days' storage, there was a significant reduction in swirling in the concentrates where BSO was added (P < 0.05).     

Testing platelet mass versus platelet count to guide platelet transfusions in the neonatal intensive care unit

BACKGROUND: Platelet (PLT) transfusions can bestow significant benefits but they also carry risks. This study sought a safe means of reducing PLT transfusions to neonatal intensive care unit (NICU) patients with thrombocytopenia by comparing two transfusion guidelines, one based on PLT count and the other on PLT mass (PLT count times mean PLT volume).
STUDY DESIGN AND METHODS: Using a prospective, two-centered, before versus after design, PLT transfusion usage and hemorrhagic events were contrasted during a period when PLT count–based transfusion guidelines were in use (Period 1) versus a period when PLT mass–based guidelines were in use (Period 2).
RESULTS: No differences were observed between Periods 1 and 2 in NICU admissions, sex, race/ethnicity, percentage of inborn patients, or percentage of patients with a PLT count less than 50 × 10⁹ or 51 × 10⁹ to 99 × 10⁹/L. In the first period 3.6% of NICU admissions received one or more PLT transfusions. This fell to 1.9% during the second period (p < 0.002). The number of PLT transfusions administered per transfused patient was the same in both periods: 2.0 (1-23) (median [range]) in Period 1 and 2.0 (1-17) in Period 2 (p > 0.40). Significantly fewer PLT transfusions were given in Period 2 for prophylaxis (patient not bleeding; p < 0.001 vs. Period 1). The number given for bleeding did not change between the two periods. In Period 2 no increases were seen in rate of intraventricular hemorrhage (IVH); Grade 3 or 4 IVH; or pulmonary, gastrointestinal, or cutaneous bleeding.
CONCLUSIONS: The use of PLT mass–based NICU transfusion guidelines was associated with fewer PLT transfusions and no recognized increase in hemorrhagic problems.     

Blood platelet kinetics and platelet transfusion

The discovery of citrate anticoagulant in the 1920s and the development of plastic packs for blood collection in the 1960s laid the groundwork for platelet transfusion therapy on a scale not previously possible. A major limitation, however, was the finding that platelet concentrates prepared from blood anticoagulated with citrate were unsuitable for transfusion because of platelet clumping. We found that this could be prevented by simply reducing the pH of platelet-rich plasma to about 6.5 prior to centrifugation. We used this approach to characterize platelet kinetics and sites of platelet sequestration in normal and pathologic states and to define the influence of variables such as anticoagulant and ABO incompatibility on post-transfusion platelet recovery. The “acidification” approach enabled much wider use of platelet transfusion therapy until alternative means of producing concentrates suitable for transfusion became available.The identification of platelets as a distinct cellular element of blood with a critical role in hemostasis in the late 1800s (1) inevitably led to speculation about platelet transfusion as a treatment for bleeding in patients with thrombocytopenia. The realization of this goal was delayed for many years by technical barriers. Development of citrate-based anticoagulants in the 1920s and flexible plastic blood containers in the 1950s–1960s made it feasible to collect blood in a plastic pack containing standard acid-citrate-dextrose (ACD) anticoagulant, centrifuge it slowly, and express the supernatant platelet-rich plasma (PRP) into a plastic side-pack for convenient transfusion. Early studies showed that platelets from multiple units of blood were needed to achieve a therapeutic effect in a bleeding patient. To prevent volume overload, this required that platelets be concentrated before being transfused. The obvious way to accomplish this was to centrifuge PRP at high speed, remove the supernatant plasma, and suspend the pelleted platelets in a small volume by gently massaging the plastic pack. It soon became apparent that concentrates prepared in this way almost invariably contained large and small platelet aggregates and few single platelets. Not surprisingly, clinicians were reluctant to transfuse these preparations. It was known at this time that platelets isolated from blood that had been anticoagulated with EDTA could be pelleted from PRP by centrifugation and dispersed without difficulty. To meet the growing demand for platelet transfusions, the Fenwal Company developed the “EDTA Platelet Pack,” consisting of a plastic collection bag containing EDTA and an attached satellite bag into which PRP could be expressed, concentrated by centrifugation into a pellet, and suspended in a small volume of plasma. Red cells were returned to the donor to enable repeated platelet donations. Despite the obvious limitations of this approach, thousands of pooled EDTA platelet concentrates were transfused in the late 1950s and the 1960s. This procedure was labor intensive, and its application was restricted to relatively few, critically ill patients.In 1961, Gardner and associates conducted seminal studies to define the pathophysiology of various thrombocytopenic disorders (2, 3). They labeled EDTA platelets with NaCr⁵¹O₄ to follow the cells after transfusion. In these studies, very few labeled platelets were detected in the peripheral blood during the first few hours after transfusion. After this time, a variable number of cells reentered circulation. The immediate sequestration of a large fraction of the transfused cells, possibly in the liver and lung (4), followed by the eventual return of some platelets into circulation was considered to be a consequence of the labeling procedure. At this time, working at the Thorndike Memorial Laboratory of the Boston City Hospital, we were similarly interested in studying platelet kinetics, and we confirmed the findings of Gardner and coworkers about the circulation kinetics of EDTA platelets. We examined PRP prepared from EDTA and ACD whole blood under phase microscopy and noted that platelet morphology was quite different in the two preparations. In ACD preparations, platelets were discoid in shape, but in EDTA preparations, they assumed an irregular, almost spherical configuration. Another striking difference was the appearance of PRP examined in a light beam while being gently agitated: ACD platelets shimmered and swirled, whereas an EDTA platelet suspension was uniform in appearance throughout. We wondered whether structural changes induced in platelets by EDTA explained the failure of most of these platelets to circulate after transfusion and carried out studies to determine whether platelet clumping in concentrates from ACD-prepared PRP could be prevented. Evaluation of several variables revealed that when the pH of ACD PRP was reduced from its starting value of about 7.2 to about 6.5 before centrifugation, the pelleted platelets could readily be dispersed, yet retained their normal discoid shape. In whole blood or in PRP, this degree of “acidification” could be achieved by simply adding an extra quantity of ACD, the anticoagulant then used routinely for blood collection. The apparent benefit of acidification persisted through repeated centrifugations and made it possible to characterize recovery and survival of ACD platelets in normal subjects (5). Our studies revealed that about 75% of the labeled ACD platelets were recovered in the recipient immediately after transfusion (Figure ​(Figure1).1). After the initial transfusion, the presence of labeled platelets in the blood steadily declined over nine days. In contrast, labeled EDTA platelets peaked in the blood around one day after transfusion and steadily declined afterward (Figure ​(Figure1).1). Scanning of body organs with a directional scintillation counter revealed that most of the radioactivity from ACD platelets not recovered in the blood was initially present in the spleen; however, transfused EDTA platelets mainly concentrated in the liver. As ACD platelets were cleared from the circulation, Cr⁵¹ accumulated in the liver and spleen, indicating that these organs are the major sites of platelet deposition. The linear clearance pattern suggested that under normal circumstances, platelets die as a consequence of “senescence,” rather than being randomly utilized (5). Open in a separate windowFigure 1Survival of autologous “citrate platelets” after transfusion to a normal subject.Approximately 75% of labeled platelets were recovered in the circulation immediately after being transfused. The red area denotes the range of blood platelet radioactivity after the injection of Cr⁵¹-labeled “EDTA platelets” on 10 occasions in 7 normal subjects. Adapted from ref. 5. Freireich and his colleagues at the National Cancer Institute soon confirmed the superiority of platelet concentrates prepared from acidified ACD blood in producing sustained platelet increases in thrombocytopenic patients (6). Over the next few years, this simple maneuver facilitated much wider use of platelet transfusions, especially in patients being treated for hematologic malignancies. We used the new methodology to characterize platelet clearance and sites of sequestration in normal individuals (5, 7) and in patients with platelet destruction mediated by alloantibodies (8) and autoantibodies (9), as well as to more fully define the role of anticoagulants and ABO incompatibility on recovery and survival of transfused platelets (10). We also demonstrated that “hypersplenic” thrombocytopenia is largely caused by pooling of a significant fraction of the total circulating platelet mass in an enlarged spleen, rather than being a consequence of suppressed platelet production or premature platelet destruction (11). Although acidifying citrated blood or PRP to prepare platelet concentrates for transfusion represented a significant improvement over what was previously possible, other advances soon followed. Mourad found that platelet concentrates prepared from nonacidified ACD blood could be manually suspended with little clumping, provided the platelet pellet was allowed to rest for some time at room temperature before manipulation (12). Other key developments were the finding by Murphy et al. that platelet viability is best maintained by storage at room temperature (13) and the evolution of pheresis systems for isolating large quantities of platelets from single donors. To my knowledge, reversible aggregation of platelets pelleted from citrated PRP is still not fully understood, but it seems almost certain that fibrinogen binding to partially activated α_IIbβ₃ integrin (GPIIb/IIIa) is involved, since fibrinogen-dependent platelet aggregation is markedly inhibited at pH 6.5 (6, 14). The EDTA-induced structural changes in platelets were well characterized by White (15). The “swirling” of platelets was shown to be a consequence of their normal discoid shape and to correlate fairly well with post-transfusion viability (16).