The prediction of post-operative deep vein thrombosis, using a newly describied test of platelet function.
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Blood Coagulation Tests↗
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Characterisation of species differences in the platelet ADP and thrombin response.
INTRODUCTION: A number of animal models are used to study platelet-dependent diseases. In the present investigation, we have used a simple flow cytometry assay to evaluate platelet function in man, rat, mouse, guinea pig and dog. MATERIALS AND METHODS: Platelet activation was evaluated in diluted whole blood by measuring fibrinogen binding to activated platelets using a polyclonal anti-human fibrinogen antibody that cross-reacts with fibrinogen from all species tested. The assay was used to evaluate platelet function with respect to ADP and thrombin sensitivity. The relative importance of the two platelet ADP receptors and total ADP in the thrombin response was also studied by using receptor-specific antagonists and apyrase, respectively. RESULTS: Mouse platelets were most sensitive to both agonists. Unlike in man and dog the maximal response to ADP was greater than to thrombin in mouse, rat and guinea pig. P2Y(12) blockade was in all species equally effective as ADP removal in inhibiting thrombin-induced platelet activation whereas P2Y(1) blockade was almost ineffective. CONCLUSION: The present study describes a simple platelet function test that can be used to evaluate platelet function in man, rat, mouse, guinea pig and dog. Platelets from the tested species differed in their sensitivity to ADP and thrombin. In contrast to human and canine platelets, mouse, rat and guinea pig platelets displayed a stronger maximal response to ADP than to thrombin. In terms of the relative contribution of P2Y(1) and P2Y(12) in the thrombin response, the P2Y(12) receptor was the key receptor in all species and its blockade gave equal effect as total removal of ADP.
Adenosine Diphosphate↗
Platelet function and plasma fibrinogen and their relations to gender, smoking habits, obesity and beta-blocker treatment in young survivors of myocardial infarction.
Seventy-three (58 men and 15 women) survivors of myocardial infarction below 45 years of age and 73 healthy matched controls were investigated regarding in vitro platelet aggregability to ADP and collagen, platelet sensitivity to prostacyclin and plasma levels of beta-thromboglobulin, platelet factor 4 and fibrinogen. The patients, studied 3-6 months after the acute event, had a reduced platelet sensitivity to prostacyclin. They did not differ from the controls regarding the other platelet function tests. Females had higher platelet reactivity than men. Smoking, obesity or beta-blocker treatment did not influence platelet function. The patients had higher fibrinogen levels than the controls. Gender did not influence, while smoking and obesity increased plasma fibrinogen. Patients on beta-blockade had lower fibrinogen levels than patients without this therapy. The high fibrinogen level and the low platelet sensitivity to prostacyclin might indicate an increased thrombotic liability in young myocardial infarction patients.
Adrenergic beta-Antagonists↗
Increased platelet aggregability during exercise in patients with previous myocardial infarction. Lack of inhibition by aspirin.
The aim of the present study was to investigate the effects of acute exercise on platelet aggregability, blood coagulation, and fibrinolysis in patients with recent myocardial infarction, and to examine these effects in relation to two different antithrombotic regimens. Forty patients (mean age 60 years) were investigated 3 months after a myocardial infarction. They were randomized to antithrombotic treatment with either warfarin (INR 2.8-4.2) or aspirin 160 mg daily. They performed a standardized ergometer bicycle exercise test. Blood was drawn before and after the exercise. The platelet function tests included a platelet aggregate ratio (PAR), which, in the presence of aggregates, is<1. The coagulation products remained largely unchanged during the exercise, whereas the fibrinolytic activity and the catecholamine levels increased significantly. At baseline, PAR was lower in the warfarin group than in the aspirin group. During exercise, PAR was significantly reduced in both study groups (0.75 vs. 0.80), indicating increased platelet aggregability. Beta-thromboglobulin decreased in both groups. The increased platelet aggregability after exercise despite aspirin is probably due to activation by catecholamines. This implies that aspirin may have a limited antithrombotic effect during physical exercise and probably also in other situations with increased catecholamine levels.
Aged↗
Intravenous ketorolac tromethamine does not worsen platelet function during knee arthroscopy under general anesthesia.
Ketorolac (KT) prolongs bleeding time and inhibits platelet aggregation and platelet thromboxane production in healthy, awake volunteers. However, platelet function may be accentuated during the stress of general anesthesia (GA) and surgery. The purpose of this study was to investigate platelet function changes during a standard GA technique and surgery, as well as after a single intraoperative dose of intravenous (i.v.) KT. The study comprised 30 ASA physical status I patients undergoing GA for knee arthroscopy. Subjects were randomized to receive either KT 60 mg IV 15 min after skin incision or placebo i.v. Platelet function testing consisted of an Ivy bleeding time (BT), platelet aggregometry (PA) with adenosine diphosphate (ADP) and collagen, thromboelastography (TEG), and serum thromboxane B2 assays (TxB2). Platelet function testing was performed: 1) 15 min prior to the induction of GA, 2) 10 min after skin incision, and 3) 45 min after administration of study drug. BT decreased significantly in the placebo group from 263 +/- 133 s (mean +/- SD) preoperatively to 207 +/- 89 s postincision. BT did not change in the KT group. PA was unchanged after IV KT. TEG data was unchanged in both groups during anesthesia and surgery. TxB2 levels decreased markedly in the KT group from 106.9 +/- 96.2 ng/mL preoperatively to 0.4 +/- 1.2 ng/mL poststudy drug, P = 0.002. Platelet function appears to be accentuated during GA and surgery as evaluated by BT in the placebo group. Further, platelet function by BT, PA, and TEG was not inhibited after i.v. KT despite near complete abolition of TxB2 production.
Adolescent↗
Storage of platelets for tests of platelet function: comparison of two methods of pH control.
A comparison was made of two methods to control the pH of platelet-rich plasma (PRP) stored for tests of platelet function. Citrated PRP at 37 degrees C was maintained at pH 7.3-7.4 by incubation either in a controlled CO2/air environment or in a plastic syringe from which all air was expelled. At intervals over 2-5 hours platelet aggregation induced by ADP and collagen was measured. Plasma beta-thromboglobulin (beta TG) was assayed to assess liberation of beta TG from platelets during storage. Platelet aggregation responses were more stable when PRP was stored in a syringe. Liberation of beta TG from platelets did not occur in this system, but did occur in the CO2 system in many experiments. The differences between the two systems were not due to the lower pO2 levels in the syringe, but were probably related to the presence of an air/liquid interface in the CO2 system. The syringe system of storage is a simple method of pH control which offers better preservation of platelet function than a controlled CO2/air environment.
Blood Platelets↗
Viscoelastic measurement of clot formation: a new test of platelet function.
Assessment of platelet function presents a challenge to the investigators in the clinical field. An instrument, Sonoclot, is described which measures changes in the viscoelastic properties (clot impedance on a vibrating probe) of plasma as it is recalcified. Platelet poor plasma (PPP) and platelet rich plasma (PRP) show distinct and characteristic Sonoclot tracings. Tracings of PPP show a lag period and a primary wave. These parameters correspond to recalcification time and fibrin polymerization. Tracings of PRP show, in addition, a secondary wave and a downward wave. These parameters correspond to the incorporation of platelets in the clot and retraction of the clot. The PRP parameters are influenced by the number and quality of the platelets. This instrument was utilized to assess the platelet function in patients after coronary artery bypass surgery (CAB). In 69 patients studied, 20 patients did not have excessive bleeding. The clot impedance tracings in this group were normal. Twenty-four patients had excessive bleeding, normal clot impedance, and coagulation tests indicating the possibility of surgical bleeding. This was confirmed in 22 (92 percent) patients upon exploration to control bleeding. Twenty-five patients had excessive bleeding, normal coagulation tests and abnormal clot impedance suggesting platelet dysfunction. In twenty-one (84 percent) of the patients, transfusion of platelet concentrate controlled the bleeding with corresponding correction of clot impedance. Sonoclot studies are quick and easy to perform, and appear to be a valuable and reliable adjunct in the diagnosis of hemostatic problems after CAB surgery.
Bleeding Time↗
Novel methodology for assessment of prophylactic platelet transfusion therapy by measuring increased thrombus formation and thrombin generation.
Currently, patients developing severe thrombocytopenia during chemotherapy treatment are prophylactically transfused with platelets. We developed two platelet function tests to report the improved haemostasis in the transfused patients, which were capable of detecting aberrant responsiveness of the platelets after transfusion. First, in a whole-blood flow test, platelet adhesion and thrombus formation were determined under high-shear flow conditions. Second, the procoagulant function of platelets was assayed in platelet-rich plasma by measurement of thrombin generation. Experimental conditions were established, where flow-induced adhesion and thrombin generation test parameters increased semi-linearly with the platelet concentration, and informed on the activation properties of platelets. The transfusion effects were evaluated for 38 thrombocytopenic patients, who were transfused with platelets stored in plasma or in synthetic medium (platelet additive solution II). In most but not all patients, transfusion resulted in increased adhesion and thrombus formation, as well as in improved platelet-dependent coagulation. Taken together, the increase in platelet count after transfusion explained 57% of the overall improvement in platelet function. In acute graft-versus-host disease, thrombus formation was normal, while platelet-dependent coagulation was higher than expected. We conclude that assessment of flow-induced adhesion and thrombin generation in acquired thrombocytopenia adequately determines the improved haemostatic activity by transfused platelets.
Acute Disease↗
Platelet function in bilateral acute retinal necrosis.
We tested platelet function in seven patients (four men and three women, ranging in age from 26 to 57 years) with bilateral acute retinal necrosis. Hyperaggregation was detected in six of the seven. Antiplatelet therapy (aspirin, 500 mg/day) together with corticosteroids or other drugs produced satisfactory results. Despite administration of antiplatelet drugs, two retinal detachments developed; both were surgically repaired. A lower dosage of antiplatelet agents in one case and late administration of it in another were thought to have caused the retinal detachments. After the acute stage was over or the retina was reattached, there were no further recurrences during a follow-up period of more than one year.
Acute Disease↗
Platelet functions in relation to diet and serum lipids in British farmers.
Coagulation and platelet aggregation induced by thrombin, ADP, adrenaline, and collagen were studied in three contrasted groups, each of 20 to 22 middle-aged male farmers. Serum lipids were similar in the three groups. In the west of Scotland group, however, platelet reactivity was significantly greater than in the east of Scotland. This was associated with a dietary intake, evaluated by three different techniques, higher in saturated fat but also lower in polyunsaturated fat and alcohol. Platelet function in the southern England group also correlated with dietary fats and in addition inversely with calcium intake. On an individual basis in the 63 farmers, all the platelet function tests were significantly correlated with the intake of saturated fat regulated by that of calcium and alcohol. The dietary effects on platelets appear to be mediated by the fatty acid composition of plasma lipids and of platelet phospholipids. In that fraction, the fatty acids 20:3 omega 9, 22:3 omega 9 and 20:4 were the most closely related to the platelet function tests. the trienoic acid 20:3 omega 9, identified with essential fatty acid deficiency, was also correlated with the intake of saturated fat and calcium. In this study, platelet functions were more dependent upon the dietary factors associated with coronary heart disease such as saturated fats, calcium, and alcohol than upon serum lipids.
Blood Coagulation↗
Identification of functional polymorphisms of the thromboxane A2 receptor gene in healthy volunteers.
Thromboxane A2 receptor (TP) is an important actor in vascular physiology and plays a crucial role in the platelet activation process. Genetic polymorphisms of the gene coding for the TP have been described, but their impacts on platelet function tests are unknown. The aim of this study was to investigate the relationship between genetic polymorphisms of the coding sequence of the TP gene and platelet function tests. We investigated 100 healthy volunteers twice, one week apart by performing platelet aggregation and secretion tests. We sequenced the coding region of the TP gene and confronted the genetic variants with the phenotypic results. We identified five single nucleotide polymorphisms (SNP); one of them, T1712C, replaces Leu by Pro at position 133 of the isoform beta of the TP. Homozygosity for the minor allele of the C795T, C924T or the G1686A SNP was associated with a decreased expression of CD62P when platelets were stimulated with the TP agonist U46619. As C795T and C924T have been linked to clinical disorders in which TxA2 plays a key role, the possible role of the G1686A and T1712C SNP should also be examined in selected diseases.
Adolescent↗
Platelet function, coagulation tests, and cardiopulmonary bypass: lack of correlation between pre-operative and intra-operative whole blood lumiaggregometry and peri-operative blood loss in patients receiving autologous platelet-rich plasma.
Platelet function and blood coagulation were studied and correlated with the post-operative red blood cell (RBC) loss in 41 patients that underwent cardiopulmonary bypass surgery. Before and after surgery, whole blood platelet aggregation and secretion were tested with different agonists, and the platelet count, prothrombin time, and activated partial thromboplastin time measured simultaneously. Post-operatively, RBC loss in chest fluid was also calculated. Platelet aggregation and secretion with different agonists (except with ristocetin and adenosine diphosphate (ADP)) were decreased significantly after protamine and platelet-rich plasma administration. There were no significant differences in aggregation and secretion immediately after cardiopulmonary bypass compared with after platelet-rich plasma administration With ADP, adenosine triphosphate (ATP) release was decreased significantly after the platelet-rich plasma infusion compared with post-protamine. Platelet count decreased significantly during surgery and remained low after platelet-rich plasma infusion. The clotting times were increased significantly after surgery, and after platelet-rich plasma infusion, the prothrombin time decreased significantly relative to the post-protamine value, the activated partial thromboplastin time being essentially unchanged. Postoperatively, the total volume of RBC collected after 36 h was 158 +/- 13 ml and there was no significant correlation with the above parameters. We conclude that pre-operative or intra-operative whole blood lumi-aggregometry is not a predictor of post-operative blood loss in patients receiving platelet-rich plasma intra-operatively.
Adenosine Triphosphate↗
Laboratory tests of platelet function.
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Blood Coagulation Factors↗
[Exploratory tests of platelet function].
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Animals↗
The role of PFA-100 testing in the investigation and management of haemostatic defects in children and adults.
The PFA-100 provides a simple global measure of high shear-dependent platelet function, and as such is not diagnostic or specific to any disorder. Prolonged closure times must be interpreted in conjunction with a full blood count, von Willebrand factor (VWF) screen and other platelet tests. The PFA-100 may also give false negative results with relatively common platelet defects. If clinical suspicion is high, further detailed platelet function testing and VWF screening are required to exclude abnormal platelet function, even if the PFA-100 is normal. In more recent studies the PFA-100 has been used for preoperative identification and management of surgical patients with haemostatic defects and for assessing the clinical effectiveness of platelet transfusion therapy. This review highlights the up to date, evidence-based, advantages and disadvantages of the PFA-100 test in the investigation and management of haemostatic disorders in both children and adults.
Adult↗
Effect of dipyridamole alone and in combination with aspirin on whole blood platelet aggregation, PGI2 generation, and red cell deformability ex vivo in man.
STUDY OBJECTIVE: The aim was to investigate the effects of dipyridamole, aspirin, and a combination of dipyridamole plus aspirin on platelet aggregation in whole blood, PGI2 generation, and red cell deformability ex vivo. SUBJECTS: were 16 male volunteers, aged 22-39 years, mean age, 26.6 years. DESIGN: This was a randomised, double blind, placebo controlled trial. The volunteer received each of the following treatments 10 days apart: dipyridamole 200 mg; aspirin 300 mg; dipyridamole 200 mg plus aspirin 300 mg; matched placebos. MEASUREMENTS AND MAIN RESULTS: Blood was taken for platelet function tests, PGI2 metabolite assay, and red cell deformability before and 2 h after the trial dose was taken. Platelet aggregation was quantified by measuring the fall in single platelet count after stimulation with 2 micrograms.ml-1 collagen or 50 nM platelet activating factor (PAF), or by rollermixing aliquots of blood to initiate spontaneous aggregation. The platelet function tests were completed at 37 degrees C within 10 min of venepuncture. The stable metabolite of PGI2, 6-keto PGF1 alpha, was measured in serum. There was inhibition of spontaneous platelet aggregation by dipyridamole (p less than 0.004), aspirin (p less than 0.005), and the combination of dipyridamole plus aspirin (p less than 0.0001) as compared with placebo. PAF induced platelet aggregation was inhibited by dipyridamole (p less than 0.002) and the combination of dipyridamole plus aspirin (p less than 0.0001) but aspirin alone had no inhibitory effect. Collagen induced platelet aggregation was inhibited by all three treatments: dipyridamole (p less than 0.06), aspirin (p less than 0.0001), and the combination of dipyridamole plus aspirin (p less than 0.0001). PGI2 generation was markedly inhibited by aspirin (p less than 0.0001) and the combination doses (p less than 0.0001) but was unaffected by dipyridamole alone. Of the three active treatments, only dipyridamole alone significantly (p less than 0.001) increased red cell deformability; there was a modest decrease in red cell deformability with aspirin. CONCLUSIONS: The results with PAF support the view that dipyridamole inhibits platelet activation by more than one mechanism; the effect on collagen induced and spontaneous platelet aggregation suggests that the effect of the combination doses is additive and that on red cell deformability the synergy is negative.
6-Ketoprostaglandin F1 alpha↗
Platelet survival, platelet factor-4 and bleeding time in myeloproliferative disorders.
In 27 patients with myeloproliferative disorders observations on thrombohaemorrhagic complications, platelet function tests and spleen size were made. Sixteen patients had thrombotic or haemorrhagic episodes. All 27 patients had elevated platelet factor-4 and 25 patients had a shortened platelet survival. Patients with myelofibrosis had a significantly shorter platelet survival than patients with polycythaemia vera (p less than 0.05). Seven out of 23 patients investigated had prolonged bleeding time. The observed abnormalities of platelet function tests were not related to thrombohaemorrhagic complications or spleen size.
Adult↗
Correlation of perioperative platelet function and coagulation tests with bleeding after cardiopulmonary bypass surgery.
The authors evaluated the correlation of post-cardiopulmonary bypass surgery bleeding, measured as 24-hour chest tube output/kilogram body weight, with platelet function tests using glass bead adhesion and Thrombelastograph Platelet Mapping (Haemoscope Corporation, Niles, Ill); coagulation tests; patient characteristics; surgery parameters; and visual assessment of surgical field bleeding before closure as not bleeding (code 1), oozing (code 2), and excessive bleeding (code 3). All platelet function and coagulation tests indicated significant dysfunction 15 minutes after protamine neutralization of heparin. With the exception of glass bead adherence, these assays indicated poor recovery of function 1 hour postoperatively. By multiple regression, the most significant predictors of postoperative bleeding were a low body mass index (BMI) (P < 0.0001), lowest core body temperature (P = 0.0006), and cross clamp time (P < 0.0001). Low core temperature was significantly (P < 0.0001) correlated with cross clamp time, which the authors believe is the most likely cause of coagulation and platelet dysfunction. None of the platelet function tests significantly correlated with bleeding. Looking at the highest quartile of chest tube output patients (n = 19) versus the upper and lower 50th percentile of coagulation and platelet function, bleeding could be explained for 11 patients by BMI plus surgery parameters along with coagulation and/or platelet dysfunction. In three cases without negative surgery parameters, coagulation dysfunction was observed. The remaining five cases did not give a clear indication of which parameters were primarily responsible for the bleeding.
Adult↗