Effect of preanalytical time-delay on platelet function as measured by multiplate,PFA-100 and VerifyNow

Background and aims: Platelet function testing may help to identify poor responders to antiplatelet drugs. The aim of this study was to compare three commonly used platelet function tests with special focus on the pre-analytical influence of time-delay on the tested parameters.

Methods: We assessed ADP-induced platelet function by the Multiplate, Platelet Function Analyzer-100 (PFA-100) and VerifyNow in nine healthy volunteers and 36 patients receiving clopidogrel or prasugrel 1 and 3?hours after sampling. Results: The PFA-100 demonstrated non-closure time in 23 patients. A more graded response could be detected with the two other devices. Aggregation in whole blood (Multiplate) decreased after 3?hours compared to 1?hour in all subjects (p?p?Conclusion: Responses to ADP are time-dependent after blood sampling for the Multiplate in all subjects and for the VerifyNow in patients on antiplatelet drugs. For both devices, platelet aggregation was reduced 3?hours after sampling which may affect data interpretation and clinical consequences.     

Evaluation of apheresis platelet concentrates stored for 5 days in PL 732 bags

To assess the functional viability of platelets collected by standard apheresis techniques using the Fenwal CS-3000 "closed system" and stored in Fenwal PL 732 plastic bags for 5 days at room temperature with agitation, a number of in vitro parameters (pH, morphology, platelet volume distribution, osmotic recovery, aggregation, and platelet-associated IgG) were examined as a function of storage time. During the first 24 hours of storage, minimal changes were observed in the test parameters with the exception of ADP-induced aggregation (75% decrease [10 uM], 84% decrease [5 microM]). Significant differences were observed between fresh (day 0) and 5-day-old platelet concentrates in all parameters except median platelet volume. These observed changes in in vitro test parameters with storage time are similar to those previously observed for comparably stored random single-donor platelet concentrates. Thus, the "closed-system" PL 732 apheresis platelet concentrates would be expected to be as effective in vivo as random single-donor platelet concentrates, while minimizing recipient exposure to transmissible agents of infectious disease.     

Platelet storage lesion in interim platelet unit concentrates: A comparison with buffy-coat and apheresis concentrates

Platelet storage lesion is characterized by morphological changes and impaired platelet function. The collection method and storage medium may influence the magnitude of the storage lesion. The aim of this study was to compare the newly introduced interim platelet unit (IPU) platelet concentrates (PCs) (additive solution SSP+, 40% residual plasma content) with the more established buffy-coat PCs (SSP, 20% residual plasma content) and apheresis PCs (autologous plasma) in terms of platelet storage lesions. Thirty PCs (n = 10 for each type) were assessed by measuring metabolic parameters (lactate, glucose, and pH), platelet activation markers, and in vitro platelet aggregability on days 1, 4, and 7 after donation. The expression of platelet activation markers CD62p (P-selectin), CD63 (LAMP-3), and phosphatidylserine was measured using flow cytometry and in vitro aggregability was measured with multiple electrode aggregometry. Higher platelet activation and lower in vitro aggregability was observed in IPU than in buffy-coat PCs on day 1 after donation. In contrast, metabolic parameters, expression of platelet activation markers, and in vitro aggregability were better maintained in IPU than in buffy-coat PCs at the end of the storage period. Compared to apheresis PCs, IPU PCs had higher expression of activation markers and lower in vitro aggregability throughout storage. In conclusion, the results indicate that there are significant differences in platelet storage lesions between IPU, buffy-coat, and apheresis PCs. The quality of IPU PCs appears to be at least comparable to buffy-coat preparations. Further studies are required to distinguish the effect of the preparation methods from storage conditions.     

Effect of platelet turnover on whole blood platelet aggregation in patients with coronary artery disease

Summary. Background: Previous studies have demonstrated considerable variation in the antiplatelet effect of aspirin. Objectives: To investigate the impact of platelet turnover on the antiplatelet effect of aspirin in patients with stable coronary artery disease (CAD) and to identify determinants of platelet turnover. Methods: Platelet turnover was evaluated by measurements of immature platelets and thrombopoietin in 177 stable CAD patients on aspirin monotherapy, including 85 type 2 diabetics and 92 non‐diabetics. Whole blood platelet aggregation was determined using the VerifyNow^® Aspirin test and multiple electrode aggregometry (MEA, Multiplate^®) induced by arachidonic acid (AA) (1.0 mm ), adenosine diphosphate (ADP) (10 μm ) and collagen (1.0 μg mL^?1). Results: Immature platelet levels significantly correlated with MEA (r = 0.31–0.36, P‐values < 0.0001) and the platelet activation marker sP‐selectin (r = 0.19, P = 0.014). Contrary to the VerifyNow^® test, MEA significantly correlated with variations in platelet count (r = 0.45–0.68, P‐values < 0.0001). Among patients with residual platelet reactivity according to AA, there were significantly more diabetics (61% vs. 41%, P = 0.027) and higher levels of sP‐selectin (77.7 ± 29 vs. 70.2 ± 25 ng mL^?1, P = 0.070) and serum thromboxane B₂ (0.81 [0.46; 1.70] vs. 0.56 [0.31; 1.12] ng mL^?1, P = 0.034). In a multivariate regression analysis, immature platelet levels were determined by thrombopoietin levels (P < 0.001), smoking (P = 0.020) and type 2 diabetes (P = 0.042). Conclusions: The antiplatelet effect of aspirin was reduced in CAD patients with an increased platelet turnover. Once‐daily dosing of aspirin might not suffice to adequately inhibit platelet aggregation in patients with an increased platelet turnover.     

Paired comparison of apheresis platelet function after storage in two containers

Platelet quality after storage strongly depends on the pre-storage quality as well as on the storage conditions determined by the storage container. In this paired study, we evaluated two different containers (MedSep CLX and Delmed DPL-110). The Fresenius AS104 cell separator was used to prepare 17 platelet concentrates that were split and distributed into the containers to be compared. Cell counts, blood gas analysis, morphological scores, glucose and lactate levels, platelet activation, and platelet aggregation were measured before splitting at the day of preparation and after storage at day 3 and day 5. At day 3, there was no significant difference between the two bags apart from increased lactate and decreased pCO(2) concentrations in the CLX bags. At day 5 there were significantly higher lactate concentrations, pO(2) levels, and aggregation after stimulation in the CLX group, while the glucose and pCO(2) concentrations were significantly lower in these platelet concentrates as compared to the DPL-110 group. However, these parameters did not influence the functional parameters tested. While the platelet quality decreased during storage in all bags, the functional changes were nearly identical in both bags tested. We conclude that both bags are equivalent for 5-day storage of platelet concentrates.     

Reversal of the anti‐platelet effects of aspirin and clopidogrel

Summary. Background: Guidelines recommend stopping aspirin and clopidogrel 7 to 10 days before surgery to allow time for replacement of permanently inhibited platelets by newly released uninhibited platelets.Objectives: The purpose of the present study was to determine the rate of offset of the anti‐platelet effects of aspirin and clopidogrel after stopping treatment and the proportion of untreated donor platelets that are required to reverse their anti‐platelet effects.Methods: Cohort 1 consisted of 15 healthy subjects who received aspirin 81 mg day^?1 or clopidogrel 75 mg day^?1 for 7 days and underwent serial blood sampling until platelet function testing results normalized. Cohort 2 consisted of 36 healthy subjects who received aspirin 325 mg day^?1, clopidogrel 75 mg day^?1, aspirin 81 mg day^?1 plus clopidogrel 75 mg day^?1 or no treatment for 7 days and underwent a single blood sampling.Results: In cohort 1, arachidonic acid (AA)‐induced light transmission aggregation (LTA) returned to baseline levels in all subjects within 4 days of stopping aspirin, coinciding with the partial recovery of plasma thromboxane B₂ concentrations. ADP‐induced LTA did not return to baseline levels until 10 days after stopping clopidogrel. In cohort 2, AA‐induced LTA in patient treated with aspirin reached control levels after mixing with 30% untreated donor platelets whereas ADP‐induced LTA in patients treated with clopidogrel reached control levels only after the addition of 90% or more donor platelets.Conclusions: Platelet aggregation recovers within 4 days of stopping aspirin but clopidogrel must be stopped for 10 days to achieve a normal aggregatory response.     

Markers of platelet activation and apoptosis in platelet concentrates collected by apheresis.

BACKGROUND: A product with well-preserved haemostatic function of platelets is the ultimate goal of platelet concentrate production. However, platelet activation and apoptosis are induced by both collection and storage of platelet concentrates. AIM OF STUDY: Platelet concentrates obtained either by two blood separators with different technology of apheresis (Haemonetics MCS+, Haemonetics Corp. Braintree, USA and Trima Accel, Gambro BCT Inc., Lakewood, USA, respectively) or derived from buffy-coat were compared using evaluation of pH, LDH, lactate, glucose, annexin V, and sP-selectin levels immediately after collecting and at the end of expiration to estimate the differences in the activation and apoptosis of platelets in these products. RESULTS: The lowest degree of platelet activation was found in products obtained by Haemonetics MCS+ apparatus at the time of collection. Platelet concentrates obtained by apheresis revealed higher rise of LDH, annexin V and sP-selectin compared to buffy-coat derived platelets. Products from Haemonetics MCS+ showed higher rise of annexin V in comparison with products from Trima separator. Increase of LDH and sP-selectin in both apheresis products was comparable. CONCLUSIONS: On the basis of changes of sP-selectin and annexin V levels it could be concluded that initial platelet activation, which is induced by apheresis, is very likely without any further impact on quality of platelets during storage. Development of platelet storage lesions is influenced especially by storage conditions and platelet concentration in products.     

The effects of irradiation on platelet function

Current medical practice involves the irradiation of blood components, including platelet concentrates, before their administration to patients with severe immunosuppression. The authors studied the effect of irradiation on in vitro platelet function and the leaching of plasticizers from the bag, both immediately and after 5 days of storage. The platelet count, white cell count, pH, glucose, lactate, platelet aggregation and release reaction, and serotonin uptake were not altered by the irradiation of random-donor or apheresis units with 2000 rads carried out at 0 and 24 hours and 5 days after collection. The leaching of di(2-ethylhexyl)phthalate from the plastic bags followed by the conversion to mono(2-ethylhexyl)phthalate was not increased by irradiation. Therefore, it is possible to irradiate platelet concentrates on the day of collection and subsequently store them for at least 5 days while maintaining in vitro function. This procedure could have considerable benefit for blood banks involved in the provision of many platelet products.     

Apheresis platelets: Emerging issues related to donor platelet count,apheresis platelet yield,and platelet transfusion dose

Emerging issues in stimulating apheresis platelet donors with platelet growth factors, the relative costs of apheresis and random donor platelet concentrates, optimal platelet transfusion dose, and leucoreduction of platelet products have caused renewed debate regarding apheresis products vs. random, pooled concentrates. The future role of apheresis products in platelet transfusion therapy will in large part be determined by costs, which are increasingly recognized to be influenced by donor platelet count, apheresis yield, and platelet transfusion dose. J. Clin. Apheresis 13:114–119, 1998. © 1998 Wiley-Liss, Inc.     

Desmopressin in vitro effects on platelet function,monitored with Multiplate,ROTEM and Sonoclot

Background and aims The vasopressin analogue desmopressin has demonstrated efficacy in decreasing bleeding time by increasing the circulating levels of coagulation factor VIII and von Willebrand factor, but also by direct effects on platelets. Previous studies have demonstrated contrasting results regarding the effect of desmopressin on platelets in vitro. The aim of this study was to investigate the dose-response effects of in vitro desmopressin in whole blood. Our hypothesis was that desmopressin could increase platelet function in anticoagulated whole blood being stored up to 4?hours. Methods Desmopressin was administered with up to four different concentrations to venous whole blood, sampled with standard vacutainer tubes from 10 healthy volunteers after consent. Platelet function was analyzed with three different point-of-care techniques: Multiplate platelet aggregometry with adenosine diphosphate, collagen, thrombin receptor activating peptide-6, ristocetin and arachidonic acid agonists, tissue factor-activated thromboelastometry and Sonoclot glass bead viscoelastic coagulation tests at baseline and 4?hours later using different activator reagents. Results Thromboelastometry and Sonoclot did not show any significant change between baseline and 4?h later. A significant decrease in area under curve (AUC) could be seen with the Multiplate between baseline and after 4?h. Desmopressin did not improve any of these tests at baseline or during a 4?h storage and incubation period. Conclusion In vitro administered desmopressin could not increase normal platelet function or coagulation being measured with thromboelastometry and Sonoclot. Multiplate indicated decreased platelet aggregation over time, without any effect of in vitro added desmopressin.     

Phosphatidylserine exposure in platelet concentrates during the storage period: differences between the platelets collected with different cell separators.

BACKGROUND AND OBJECTIVES: Platelet alterations occur during the production and storage of platelet concentrates, the so called "storage lesion". We studied the platelet alterations during the storage period in apheresis concentrates, employing flow cytometry for phosphatidylserine (PS) detection on platelets during the five days of storage. MATERIAL AND METHODS: Twenty-seven single donor platelet concentrates harvested with the Cobe Trima, Baxter Amicus, or Haemonetics MCS+ were analyzed for PS exposure by flow cytometry on the day of production (day 1) and on days 3 and 5 of storage. Furthermore PS expression was analyzed in platelet donors' blood samples withdrawn before plateletpheresis. RESULTS: PS expression on platelets gave the following median values: in blood donors before apheresis it was 1.12% (0.13-1.78) in platelets concentrates on the first day (2 h after apheresis) 2.06% (0.66-15.2), the third day 6.57% (1.98-51.13) and the fifth day 23.04% (3.86-80.23). All differences between median values of PS expression in blood samples before apheresis, and platelets concentrates on days 1, 3 and 5 of storage, are statistically significant. The expression of PS in platelet concentrates was analyzed in relation to the blood cell separator used for the collection procedure and showed the following results: on day 1 the median values of PS in platelet concentrates collected with the three different blood cell separators, Trima, Cobe and MCS, did not show statistically significant differences. On day 3, the platelets concentrates collected with the Trima and with the MCS showed differences that were statistically significant. Those were respectively 10.59% (4.56-51.13) and 3.53% (1.98-12.61), p = 0.005. The PS expression in platelet concentrates collected with the Trima and MCS showed differences that are also statistically significant on day 5 at respectively 32.4% (9.61-80.23) and 8.57% (3.86-48.42), p = 0.005. CONCLUSIONS: PS exposure in platelet concentrates on days 3 and 5 rise to levels that could compromise the quality of the platelet units. Improvements in standardized platelet quality controls, and in platelet collection systems are required to reduce the storage lesions in platelets concentrates.     

Effect of diltiazem and a prostaglandin derivative (PGBx) on platelet function during long-term storage

Calcium is an intermediate messenger between platelet stimuli and platelet response. Published studies have shown that the decreased ability of platelets to control calcium flux during long-term storage leads to platelet senility. Platelet metabolism might be more efficient during storage if pharmacologic agents that limit calcium movement were incorporated into the platelet concentrate storage solution. This hypothesis was tested by storing platelets with the calcium channel blocker, diltiazem, or with a prostaglandin B1 derivative, PGBx. During a 15-day storage period, platelets incubated with either diltiazem or PGBx showed improved function, as measured by aggregation, as compared to control platelets. The PGBx -enhanced platelet function during storage was accompanied by a significant decrease in glucose and an increase in adenosine triphospate concentrations. Platelet function after storage with PGBx improved in spite of significantly lower pH levels of the platelet concentrates at all time points tested. These studies suggest that the maintenance of calcium ion homeostasis during long-term platelet storage is important to in vitro platelet function even if the Ca2+ balance is maintained at the expense of pH and the glucose concentrations.     

Quality of irradiated and non-irradiated plateletpheresis concentrates stored in platelet additive solution

Introduction

Platelet additive solutions (PAS) allow to maintain platelet storage properties in platelet concentrates (PCs). The aim of the present study was to evaluate the in-vitro quality of irradiated and non-irradiated PCs, suspended in PAS, over a storage period of 6 days.

Determinants of high on-treatment platelet reactivity and agreement between VerifyNow and Multiplate assays

Dual antiplatelet therapy with clopidogrel is a regimen used before and after drug-eluting stent (DES) implantation. Point-of-care platelet reactivity assays are easy-to-use methods to determine adequate response to the drug. The aim of this study was a comparison of the two platelet reactivity assays: Multiplate^® and VerifyNow^® and an identification of factors potentially influencing the results of these tests, including common genetic polymorphisms. The study included 39 patients receiving 75?mg clopidogrel daily before angioplasty with DES implantation. Platelet reactivity was measured with Multiplate and P2Y₁₂ VerifyNow assays. Genetic polymorphisms of CYP2C19*2, ABCB1 3435C?>?T, and CYP3A4*1G were determined with PCR-RFLP method and CYP2C19*17 was determined by means of an allele-specific PCR. Agreement between Multiplate and VerifyNow assays was poor (Cohen’s κ?=?0.056, p?=?.273). Hematocrit significantly negatively correlated with VerifyNow assayed platelet reactivity (r?=??.487, p?=?.002). Female sex was significantly associated with higher VerifyNow assay results after adjustment to hematocrit (253.2?±?47.6 PRU vs. 195.9?±?56.9 PRU, p?=?.013) and the prevalence of high-on-treatment platelet reactivity (OR: 8.50; 95% CI 1.13–77.60, p?=?.024). Reactivity measured with Multiplate was lower in women (82.3 vs. 175.6?AU·min, p?=?.037) and in patients who received calcium channel blockers (74.7 vs. 191.7?AU·min, p?=?.002). None of the studied polymorphisms significantly influenced platelet aggregation measurements. In conclusion, different aspects modify between-patient variability of the Multiplate and VerifyNow assays and agreement between those two assays was poor.     

Preparation and storage characteristics of white cell-reduced high-concentration platelet concentrates collected by anapheresis system for transfusions in utero

BACKGROUND: Important concerns with regard to in utero platelet transfusions are avoidance of volume overload and the immunomodulatory effects of residual white cells (WBCs). This study evaluated a modification of a leukocyte‐reduction system (LRS, Spectra, COBE BCT) for apheresis, which collects high‐concentration WBC‐reduced platelets (HCPs) for in utero transfusion. STUDY DESIGN AND METHODS: The LRS procedure was modified by running the platelet collection pump at specified low flow rates (Q_col) for the first part of the procedure, collecting HCPs by gently purging them from the LRS chamber into a designated collection bag and then restoring the original LRS procedure settings to collect a second standard apheresis platelet concentrate (PC). Two centers carried out 32 procedures. Platelet yield, residual WBCs, and in vitro platelet function studies were evaluated. RESULTS: Platelet concentrations in 60 mL of HCPs were predictable according to Q_col (r² = 0.735). HCP yields varied from 0.9 to 3.2 × 10¹¹, depending on the desired final platelet concentrations in 60 mL, with an overall average of 1.92 × 10¹¹ (n = 32). Apheresis PCs had a mean platelet yield of 2.9 × 10¹¹ (1.3‐4.4 × 10¹¹, n = 20) and 3.9 × 10¹¹ (2.2‐5.8 × 10¹¹, n = 12) at concentrations of 1.3 × 10¹² per L for single‐needle and dual‐ needle procedures, respectively. Median WBC counts were 5.6 × 10³ for HCPs and 2.0 × 10⁴ for apheresis PCs, with >99 percent expected to be less than 1 × 10⁶. HCP in vitro characteristics were equivalent to those of apheresis PCs at 24 hours after collection. In vitro performance declined over storage as a function of HCP yield. HCP pH at 22^oC was maintained at a level of >6.2 for more than 3 days for yields >1.6 × 10¹¹, less than 2 days for yields 1.6 to 2.2 × 10¹¹, and less than 24 hours for yields >2.2 × 10¹¹. HCPs showed good in vitro characteristics and could be stored for 1 to 3 days, depending on the total number of platelets collected. CONCLUSION: A standard apheresis PC and an HCP requiring no secondary processing can be collected with the Spectra LRS. The platelet concentration may be determined by clinical need. HCPs meet the requirements for components that are transfused in utero.     

Role of mitochondria in the maintenance of platelet function during in vitro storage

Aims/Objectives: Platelets undergo structural and biochemical alterations during in vitro storage and these are collectively called platelet storage lesions (PSL). The mitochondrion is an important cell organelle involved not only in energy production but also in the regulation of cellular functions and viability. This implies that some platelet functions may be regulated by mitochondria; hence, preservation of mitochondrial functions may be important for the maintenance of platelet quality in stored platelet concentrates (PCs). This work describes the effects of various compounds on mitochondrial functions important for the maintenance of platelet quality in in vitro stored PCs. Methods: PCs were stored at 22 °C with gentle agitation in the presence or absence of 2,4‐dinitrophenol, antimycin A, acetyl‐l ‐carnitine and ascorbic acid. The effects of these products on platelet quality were assessed by analysing glucose and lactate concentrations, pH of the storage medium, shape of the platelets, mitochondrial membrane potential and depolarisation, surface expression of CD62P and collagen‐induced platelet aggregation. Results: 2,4‐Dinitrophenol and antimycin A increased PSL levels, whereas acetyl‐l ‐carnitine reduced the level of changes in pH and mitochondrial depolarisation. Ascorbic acid in the storage medium resulted in improved levels of collagen‐induced platelet aggregation. However, none of the examined reagents suppressed CD62P expression in platelets. Conclusions: These results suggest that preservation of mitochondrial function is fundamental, but not fully sufficient, for the maintenance of platelet in vitro quality during storage. Further research is necessary to develop methods for preserving both mitochondrial and platelet functions in in vitro stored PCs.     

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).     

机采血小板保存期内血小板聚集功能和可溶性P-选择蛋白的变化

本研究探讨保存期内的机采血小板的聚集功能和可溶性P-选择蛋白含量的改变。收集20份机采血小板样品，分别在保存期第1天（0—24小时）、第2天（24—48小时）、第3天（48—72小时）、第4天（72—96小时）和第5天（96—120小时）检测血小板的聚集功能和可溶性P-选择蛋白含量。结果表明：以ADP作为诱导剂，保存期内机采血小板的血小板聚集功能降低明显，与第1天组比，组间差异均有统计学意义（P均〈0．01），第4天组的血小板最大聚集率≤3％；血浆可溶性P-选择素含量则随着保存时间的延长逐渐升高，与第1天组比，组间差异均有统计学意义（p均〈0．05）。结论：机采血小板在保存期内存在持续活化，且聚集功能下降明显，从第4天开始几乎已完全丧失对ADP的致聚反应，提示机采血小板的体外保存损伤应该引起高度重视。     

The effect of storage on the expression of platelet membrane phosphatidylserine and the subsequent impacton the coagulant function of stored platelets

BACKGROUND: Platelet concentrates (PCs) derived from whole blood and stored under standard blood bank conditions undergo changes that are referred to as the platelet storage lesion. This study assesses the effect of PC preparation and storage on the distribution of phosphatidylserine (PS) in the platelet membrane and the effect that this distribution may have on the thrombogenic potential of stored PCs. STUDY DESIGN AND METHODS: Fresh platelets and PCs donated by healthy donors were obtained. PCs derived from platelet-rich plasma were studied on Day 1, Day 3, and Day 6 of storage under blood bank conditions. RESULTS: Platelet aggregation after exposure to the platelet agonists ADP and epinephrine singly declined progressively, but, when ADP and epinephrine in combination and collagen and thrombin in combination were used as agonists, the decline in platelet aggregation was less marked. PS expression as measured by Annexin V binding (mean and SD) was 2.02 +/- 0.93 percent in fresh platelet samples and increased to 5.39 +/- 4.2 percent on Day 1, 22. 1 +/- 7.1 percent on Day 3, and 39.5 +/- 12.1 percent on Day 6. Platelet prothrombinase activity (mean +/- SD) as measured by thrombin generation increased from 1.49 +/- 0.7 micro per mL in fresh platelet samples to 3.68 +/- 1.1 micro per mL in Day 1 platelets (p<0.001), 5.15 +/- 2.5 micro per mL in Day 3 platelets (p<0.001), and 4.65 +/- 2.48 micro per mL in Day 6 platelets (p<0. 001). CONCLUSION: These results show that PS expression increases after preparation of PCs from platelet-rich plasma and rises progressively during platelet storage under blood bank conditions. Furthermore, the greater PS expression is associated with increased platelet- dependent thrombin-generating capacity.     

Effects of nitric oxide on platelet activation during plateletpheresis and in vivo tracking of biotinylated platelets in humans

BACKGROUND: The use of platelet transfusions has risen considerably over the last few years, which leads to the collection and transfusion of a greater number of donor plateletpheresis units. Plateletpheresis activates platelets in platelet concentrates, which determines the degree of the storage lesion subsequently observed. STUDY DESIGN AND METHODS: As nitric oxide (NO) is a potent inhibitor of platelet aggregation and activation, a placebo-controlled crossover trial was performed in healthy young male volunteers to determine whether the NO-donating compound, sodium nitroprusside (SNP), decreases platelet activation during apheresis and whether activated (p-selectin+) platelets circulate in vivo after transfusion. The study also investigated whether nonradioactive biotin labeling of apheresis platelets is feasible for the study of platelet recovery after transfusion in humans. RESULTS: Platelet activation increased after plateletpheresis in the platelet components, but SNP did not inhibit platelet activation during apheresis, as measured by the percentage of p-selectin expression and the secretion of soluble p-selectin and RANTES. Only a minor increase in p-selectin+ platelets was seen in peripheral blood at 60 minutes after transfusion of the platelets, a rise that was considerably less than that calculated in p-selectin+ platelets if they all were recovered as activated platelets after transfusion. Biotin-labeled platelets averaged 1.5 percent at 10 minutes after transfusion and increased slowly to 2.6 and 3.4 percent after 60 minutes and 24 hours, respectively (p<0.05). CONCLUSION: SNP does not decrease platelet activation during apheresis and subsequent storage, and only a minor proportion of activated (p-selectin+) platelets circulate after transfusion in men. Moreover, biotin labeling of PCs can safely be used in humans for the study of platelet recovery after transfusion, and measuring recovery at 1 hour may lead to an underestimation of the true recovery when activated platelets are transfused.