Platelet Function Analyzer PFA-100 Research Articles

Perioperative Monitoring of Primary and Secondary Hemostasis in Coronary Artery Bypass Grafting

On-pump cardiac surgery is accompanied by complex alterations of hemostasis. The excessive postoperative bleeding has been attributed to acquired platelet dysfunction, impaired plasmatic coagulation, and increased fibrinolysis. The characterization of the hemostatic defects responsible for bleeding is crucial for specific treatment and optimal clinical management of the patient. For rapid determination of platelet-dependent primary hemostatic capacity (PHC), the Platelet Function Analyzer PFA-100 system is available. To evaluate the PFA performance in perioperative monitoring, a study was performed in 49 patients selected for low bleeding risk undergoing selective primary coronary artery bypass grafting (CABG). We compared PHC with Simplate bleeding time (BT) and platelet aggregometry. Furthermore, we analyzed global hemostasis by thromboelastography (TEG) and plasmatic coagulation by standard clotting tests prothrombin time (PT, Quick), activated partial thromboplastin time (aPTT), thrombin time (TT) and clotting factors and fibrinolysis by batroxobin (reptilase) time (RT). In all patients BT was postoperatively increased by 1.5- to 2-fold irrespective of perioperative complications and decreased to mildly prolonged values on the first postoperative day (1st day). In patients without complications, PHC in both collagen-adenosine diphosphate closure time (CADP-CT: 83 seconds preop, 78 seconds postop, and 74 seconds 1st day) and collagen-epinephrine closure time (CEPI-CT: 98 seconds preop, 95 seconds postop, 85 seconds 1st day) remained nearly stable. Apart from a patient with postoperative moderate thrombocytopenia, in bleeding patients no other significant defect of postoperative platelet hemostatic capacity was observed. However, on 1st day, the PHC of those patients was significantly reduced compared with non-bleeding patients. In patients with postoperative myocardial ischemia, increased PHC was identified by significantly shorter postoperative CADP-CT (66 seconds vs. 83 seconds) than in uncomplicated patients. By aggregometry, partial platelet dysfunction was observed in some patients without correlation to bleeding complications. In seven of 9 patients the postoperative bleeding complication was attributed to prolonged heparin anticoagulation and/or mildly enhanced fibrinogenolysis/fibrinolysis by TEG and standard plasmatic coagulation tests (TEG: k time 18 minutes vs. 8 minutes; aPTT: 47 seconds vs. 32 seconds; TT: 18.0 seconds vs. 12.3 seconds) and (RT: 19.5 seconds vs. 17.7 seconds). The impairment of PHC, platelet aggregation, and clotting factors observed on the 1st day in bleeding and in intra-aortic balloon pump (IABP) patients are most likely secondary effects, for example, loss of active platelets and clotting factors, to the primary postoperative bleeding or implantation of the IABP. In conclusion, our data indicate that in standard CABG procedures highly variable alterations of the hemostatic system occur after cardiopulmonary bypass (CPB) even in patients with assumed low operative risks. For identification of post-CPB bleeding complications, thromboelastography, aPTT, and TT and heparin and batroxobin (reptilase) time as fibrinolysis-sensitive assays are useful. Platelet function appears to be rapidly restored in uncomplicated CABG. PHC determination by PFA-100 demonstrates a high specificity for adequate platelet function and, therefore, could be beneficial in improved transfusion of platelet concentrates. PHC testing by PFA-100 may help identify postoperative platelet hyper-reactivity associated with myocardial lesion.

Platelet activation can occur by shear stress alone in the PFA-100 platelet analyser

The PFA-100 platelet function analyser simulates high-shear platelet function; however, the relative importance of the high shear rates alone has not been examined in this system. Normal blood was analysed by the PFA-100 using modified cartridges that contained a blank membrane lacking the usual platelet agonists (collagen/epinephrine or collagen/ADP) thus isolating the effects of shear stress alone. We found evidence of platelet activation with significant increases in platelet–leucocyte aggregates. There was no significant change in surface CD62P nor PAC-1 expression. A degree of platelet activation occurs in the PFA-100 due to shear stress alone.

The influence of the haematocrit on primary haemostasis in vitro

Primary haemostasis consists of platelet adhesion to subendothelial collagen, their activation and aggregation and finally the formation of a platelet plug. Erythrocytes are involved in this process because they flow in the center of the vessel and push platelets towards the site of action on the vessel wall and enhance shear forces, which activate platelets. In the platelet function analyzer PFA-100 (Dade Behring, Düdingen, Switzerland), the in vivo situation is simulated in vitro with blood being aspirated at high shear rates (5000s(-1)) through a capillary into a membrane pore with a diameter of 150 microm coated with type I collagen and either epinephrine or adenosine diphosphate. Aggregating platelets plug the pore and stop the flow, which is measured as the closure time. We analysed the influence of erythrocytes on platelet function analyzer measurements by systematic variation of the haematocrit (20, 30, 40, and 50%) at constant platelet counts of 289 +/- 61 x 10(3)/microl plasma, or 152 +/- 30 x 10(3)/microl blood, 96 +/- 9 x 10(3)/microl blood and 54 +/- 5 x 10(3)/microl blood, respectively. An inverse correlation was found between haematocrit and closure time under all circumstances. A decrease of the platelet count by 50 x 10(3)/microl could be compensated for by a 10% increase in haematocrit. The haematocrit must, therefore, be taken into consideration for the correct interpretation of PFA-100 measurements. Our data also provide a pathophysiological rationale to reduce the risk of bleeding in patients with thrombocytopenia and anaemia by normalizing the haematocrit with erythrocyte transfusions.

3. Internationales Symposium: „Autologe Transfusion - Von der Euphorie zur Ratio: Praktisches Handeln aus wissenschaftlicher Sicht” (Teil III)Does Hemodilution Enhance Coagulability?

Recent publications reported enhanced coagulability in hemodilution determined by TEG. In contrast, earlier reports have shown prolongation of in-vivo bleeding time in anemia. In order to take a closer look at this discrepancy undiluted and diluted anticoagulated blood samples (20 % with saline solution, hydroxyl-ethyl starch 6 % (HES), autologous platelet poor plasma (PPP)) were investigated by TEG (n = 10), ball (n = 10), and hook coagulometer (n = 15) as well as tests simulating primary hemostasis ex vivo (Platelet Function Analyzer PFA-100, n = 10). Dilution with plasma changed TEG parameters in a way, when started by recalcification of the blood sample, which is characteristic of enhanced coagulability (r decreased in all and k in 8 of 10 samples, maximal amplitude increased in 9 out of 10). With HES, changes in TEG parameters mainly indicated reduced coagulability (k increased in 7 out of 10, MA decreased in 10 out of 10). When the coagulation was additionally activated by PTT reagent (InTEG) the TEG parameters also mainly showed hypocoagulation with the three dilution solutions. Coagulation times with ball and hook coagulometers were significantly prolonged by dilution especially with saline (+ 25 % and + 17 %, p < 0.001). Dilution always significantly (often abnormally) prolonged closure time in PFA-100 (saline + 41 +/- 18 %, PPP + 37 +/- 20 %, HES + 69 +/- 24 %) demonstrating disturbance of primary hemostasis, particularly with HES. From the results obtained it can be concluded that the changes in the classical TEG (without addition of PTT-reagent), suggesting an enhanced coagulability, may be caused methodically as they are also found with autologous PPP. On the other hand, a disturbance of the primary hemostasis in hemodilution has to be taken into account from the results seen with the PFA-100 and a number of published data.

An in vitro model for the detection of reduced platelet sensitivity to acetylsalicylic acid

A discovery of 'aspirin resistance' has prompted the search for fast and reliable methods for the monitoring of antiplatelet efficacy of acetylsalicylic acid (ASA). Our aims were: (1) to evaluate the in vitro model-based method for detecting a reduced platelets' sensitivity to ASA using a point-of-care platelet function analyser PFA-100; and (2) to propose a simple method of data analysis that might be successfully employed to discriminate between 'good' and 'poor' responders to aspirin. Whole blood platelets from healthy volunteers were incubated in vitro with 30 microg/ml ASA (the in vitro method under evaluation) or analysed following a 10-day intake of an average 150 mg ASA (Aspirin Protect) daily (the reference ex vivo method). According to polynomial regression analysis of the bimodally distributed data, the donors with lower ('ASA poor responders') or higher platelet sensitivity to ASA ('ASA good responders') were discriminated at 58.6% of platelet function inhibition. Despite the similar proportions of 'ASA poor responders' (44 versus 41% using the ex vivo and in vitro tests, respectively), 30% of discordant classifications point to a rather unsatisfactory convergence between both methods. Due to a considerable discordance between the in vitro and ex vivo tests of ASA efficacy performed with the use of the PFA-100 system, the former cannot be reliably and interchangeably used for the monitoring of aspirin therapy and the selection of an effective therapeutic ASA dose. A novel approach to data analysis of the distribution of platelet inhibition rates facilitates an evaluation of cut-off points required to discriminate between 'poor responders' and 'good responders' to aspirin.

Comparison of structured use of routine laboratory tests or near-patient assessment with clinical judgement in the management of bleeding after cardiac surgery

Using algorithms based on point of care coagulation tests can decrease blood loss and blood component transfusion after cardiac surgery. We wished to test the hypothesis that a management algorithm based on near-patient tests would reduce blood loss and blood component use after routine coronary artery surgery with cardiopulmonary bypass when compared with an algorithm based on routine laboratory assays or with clinical judgement. Patients (n=102) undergoing elective coronary artery surgery with cardiac bypass were randomized into two groups. In the point of care group, the management algorithm was based on information provided by three devices, the Hepcon, thromboelastography and the PFA-100 platelet function analyser. Management in the laboratory test group depended on rapidly available laboratory clotting tests and transfusion of haemostatic blood components only if specific criteria were met. Blood loss and transfusion was compared between these two groups and with a retrospective case-control group (n=108), in which management of bleeding had been according to the clinician's discretion. All three groups had similar median blood losses. The transfusion of packed red blood cells (PRBCs) and blood components was greater in the clinician discretion group (P<0.05) but there was no difference in the transfusion of PRBCs and blood components between the two algorithm-guided groups. Following algorithms based on point of care tests or on structured clinical practice with standard laboratory tests does not decrease blood loss, but reduces the transfusion of PRBCs and blood components after routine cardiac surgery, when compared with clinician discretion. Cardiac surgery services should use transfusion guidelines based on laboratory-guided algorithms, and the possible benefits of point of care testing should be tested against this standard.

Platelet function in mitochondriopathy with stroke and stroke-like episodes.

Stroke and stroke-like episodes are frequent complications in mitochondriopathy, particularly in MELAS syndrome (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke like episodes) which is a disorder of the mitochondrial oxidative metabolism in diverse cell types. To clarify a possible pathological aspect of stroke in these patients, we investigated platelet function before and after physical exercise. Ten patients with mitochondriopathy and stroke and ten healthy sex and age matched controls were investigated in an analyst blinded, prospective cross-sectional trial. Exercise decreased intraplatelet adenosine triphosphate (ATP) concentrations by -22% from baseline in patients with mitochondriopathy (p<0.01 between groups) while exercise increased ATP-levels by 28% healthy controls (p=0.01 vs baseline). Thrombin receptor activating peptide (TRAP) stimulated P-selectin expression increased up to 50% (p<0.05) in healthy subjects following exercise compared to 39% (p>0.05) in patients with mitochondriopathy. Exercise trendwise decreased platelet plug formation under shear stress by 24% in patients as measured by the platelet function analyzer PFA-100(R). Tromboelastography showed firm thrombus formation and delayed lysis in patients following exercise. In conclusion, this trial has shown that ATP depletion during and after exercise probably accounts for a defective oxidative metabolism in platelets of patients with mitochondriopathy and stroke. This might induce decreased platelet function in these patients but fails to explain the increased stroke rate. Therefore other mechanisms seem to be etiologically involved in the pathogenesis of stroke in patients with mitochondriopathy.

Influence of Platelet Count, Acetylsalicylic Acid, von Willebrand’s Disease, Coagulopathies, and Haematocrit on Results Obtained Using a Platelet Function Analyser in Dogs

The platelet function analyser PFA-100 aspirates blood in vitro from a sample reservoir in disposable test cartridges through a microscopic aperture cut into a biologically active membrane at the end of a capillary. In different cartridges the membrane is coated with collagen and adenosine diphosphate (ADP) or collagen and epinephrine (adrenaline) inducing a platelet plug and closure of the aperture. The closure time and total volume of blood flow through the capillary until closure of its aperture were measured. The correlation between platelet count in samples of thrombocytopenic dogs and results of the collagen/ADP cartridge (closure time: r S=−0.579; total volume: r S=−0.549) was closer than between platelet count and capillary bleeding time. No significant correlation was observed between platelet count and the results obtained with the collagen/epinephrine cartridge. In addition, a higher sensitivity was obtained for the collagen/ADP cartridge. Injection of acetylsalicylic acid into healthy dogs significantly increased closure time and total volume of both types of cartridges ( P<0.01). Two dogs with von Willebrand’s disease had abnormal values. In contrast, coagulopathies did not significantly influence the results of the platelet function analyser ( P>0.05). Despite adequate sensitivity of measurements using the collagen/ADP cartridge to assess quantitative and qualitative platelet disorders in dogs, the influence of haematocrit ( P<0.0001) will limit the clinical application of the analyser.

Clinical application of the PFA-100.

The PFA-100 (platelet function analyzer) is a relatively new tool for the investigation of primary hemostasis. Recent studies have shown its utility as a screening tool for investigating possible von Willebrand disorder (VWD) and various platelet disorders. More recently, the PFA-100 has been shown to be valuable in monitoring desmopressin acetate (DDAVP) therapy in both VWD and platelet disorders. The PFA-100 has also been evaluated in many other studies for its utility in assessing drug effects, for potential monitoring of antiplatelet medication (including aspirin), or for evaluation of overall primary hemostasis in various clinical disorders or during surgical procedures. This article reviews current findings and highlights the benefits and limitations of the clinical utility of the PFA-100. Ultimately, the greatest strengths of the PFA-100 are its simplicity of use and excellent sensitivity to particular hemostatic disturbances such as VWD, platelet disorders, and platelet-affecting medication. However, because it is thus a global test system, this also creates a significant limitation because the PFA-100 is not specific for, nor predictive of, any particular disorder. However, used appropriately, the PFA-100 can be considered a worthwhile addition to any hemostasis laboratory involved in the diagnosis or therapeutic monitoring of bleeding disorders and potentially of antiplatelet medication. This review should be valuable to both hemostasis scientists and clinical specialists.

Determination of platelet aggregation inhibition during percutaneous coronary intervention with the platelet function analyzer PFA-100

Background A simple device to rapidly evaluate platelet function may aid in optimizing glycoprotein IIb/IIIa inhibition during percutaneous coronary intervention (PCI). We prospectively studied platelet function in 250 patients receiving abciximab or eptifibatide during PCI. Methods and Results The platelet function analyzer PFA-100 (Dade-Behring, Deerfield, Ill) measures platelet function by determining the time to occlusion of an aperture in a biochemically active membrane as whole blood flows under high shear conditions. Platelet aggregation causes aperture occlusion, and results are reported as a closure time (CT). All patients received either abciximab or eptifibatide, along with aspirin and heparin; patients undergoing stent implantation received aspirin and a thienopyridine postprocedure. The CT was measured at baseline and 10 minutes, 4 hours, 12 hours (abciximab-only), and 24 hours after the bolus. Profound inhibition was exhibited in most patients shortly after the platelet inhibitor bolus and during the course of therapy. We observed recovery of platelet function 12 hours after discontinuation of abciximab, with a high degree of interpatient variability, and ongoing profound platelet inhibition 4 to 6 hours after the discontinuation of eptifibatide. Among patients treated with abciximab, patients who were obese recovered from platelet inhibition sooner than patients who were not obese, whereas patients who were elderly had delayed recovery compared with patients who were not elderly. Failure to achieve maximal platelet inhibition (nonclosure) at 10 minutes indicated a possible association with adverse clinical events at the 6-month follow-up examination (60% vs 20%). Conclusions PFA-100 is a rapid simple assay used as a means of assessing inhibition of platelet aggregation during PCI performed with glycoprotein IIb/IIIa inhibition. Failure to achieve nonclosure early after the initiation of abciximab therapy warrants further investigation because there may be an association with adverse cardiac events at 6-month follow-up. (Am Heart J 2002;144:151-8.)

Systemic platelet effects of contrast media: Implications for cardiologic research and clinical practice

Background Angiographic contrast media cause platelet activation and decrease aggregability in vitro. We have previously shown in vitro a significant antiplatelet effect of contrast media at the concentrations obtained locally in the coronary artery during angioplasty. It is not known, however, whether a systemic effect is present. Method Thirty patients undergoing diagnostic coronary angiography were prospectively randomized to receive the nonionic medium iohexol, ionic low-molecular-weight medium ioxaglate, or ionic high-molecular-weight medium diatrizoate. Platelet aggregability was measured before and after the investigation with whole blood electrical impedance aggregometry (WBEA) with collagen agonist and the PFA-100 (Dade, Miami, Fla) platelet function analyzer with combined shear, collagen, and adenosine diphosphate as agonists. Results With WBEA, with iohexol no difference in impedance change was seen: (medians and ranges) before, 9.8 Ω (4.8-19.2 Ω) versus after, 9.6 Ω (2-19.2 Ω) (P not significant [NS]). With ioxaglate a significant fall was seen: before, 8.6 Ω (6.4-15.2 Ω) versus after, 6.6 Ω (0-12.4 Ω) (P =.004). With diatrizoate a significant and greater fall was seen: before, 10.8 Ω (6.4-17.6 Ω) versus after, 6.6 Ω (0-10.8 Ω) (P =.002). With PFA, no difference in closure time was seen with any medium: iohexol before, 99 seconds (79-142 seconds) versus after, 142 seconds (63-128 seconds) (P NS); ioxaglate before, 120 seconds (75-258 seconds) versus after, 95 seconds (74-258 seconds) (P NS); and diatrizoate before, 114.5 seconds (65-250 seconds) versus after, 100.5 seconds (72-300 seconds) (P NS). Conclusions Ionic but not nonionic contrast media have a systemic antiplatelet effect at diagnostic angiographic doses when measured with WBEA. Such an effect has not been shown before. This may explain the observed improved clinical outcome with ionic contrast media but also might confound platelet studies in coronary angioplasty. (Am Heart J 2002; 143:e1.)

Retracted: Changes of haemostasis in patients undergoing major abdominal surgery—is there a difference between elderly and younger patients?

Many physiological functions are altered in the elderly. It is not clear whether this applies to haemostatic mechanisms in patients undergoing major surgery. Twenty-five consecutive patients <60 yr and 25 consecutive patients >70 yr scheduled for abdominal surgery for malignancies were included in our study. Various standard coagulation variables and specific markers of coagulation were serially measured before surgery (baseline), at arrival on the intensive care unit (ICU), 4 h after arrival on ICU, and on the morning of the first postoperative day. Platelet function was assessed using the Platelet Function Analyser PFA-100 with adenosine diphosphate (ADP) as an inductor. Anaesthesia and surgery were similar between the elderly (76(3) years) and younger (53(5) years) groups. Baseline plasma levels of prothrombin fragments F1+2, thrombin-antithrombin III (TAT) complex, and D-dimers were significantly different between the two groups, indicating thrombin activation and fibrin formation in the elderly. Postoperatively, only F1+2 plasma levels were significantly higher in the elderly (4.0(0.8) nmol/l) than in the younger patients (2.2(0.9) nmol/l), whereas the course of D-dimer and TAT did not differ significantly between the two groups. Endothelial-derived markers of coagulation (von Willebrand factor, collagen-binding activity of von Willebrand factor) were not different between the groups throughout the study period. Platelet function was impaired in the elderly compared with the younger patients. It is concluded that elderly patients showed more prothrombin activation/thrombin generation and increased fibrinolytic activity prior to surgery than younger patients. However, perioperative changes of coagulation in the elderly were similar to those seen in younger patients.

Utility of the PFA-100 for assessing bleeding disorders and monitoring therapy: a review of analytical variables, benefits and limitations.

The PFA-100 (platelet function analyser) is a relatively new tool for the investigation of primary haemostasis. Recent studies have shown its utility in monitoring antiplatelet therapy (including aspirin) and as a screening tool for investigating possible von Willebrand disease (vWD) and various platelet disorders. More recently, the PFA-100 has been shown to be of value in monitoring DDAVP therapy in both vWD and platelet disorders. This paper reviews current findings, details the utility of the PFA-100 for some of these purposes, as well as reviewing analytical variables that may complicate the interpretation of results. The author highlights the benefits, as well as noting the limitations, of its use. Ultimately, the greatest strengths of the PFA-100 are its simplicity in use and excellent sensitivity to particular haemostatic disturbances such as vWD, platelet disorders and platelet-affecting medication. However, because it is thus a 'global' test system, this also creates a significant limitation, as the PFA-100 is not specific for, nor predictive of, any particular disorder. However, utilized appropriately, the PFA-100 can be considered a worthwhile addition to any haemostasis laboratory involved in the diagnosis or therapeutic-monitoring of bleeding disorders including vWD and platelet-dysfunctions. This review should be of value to both haemostasis scientists and clinical specialists.

Rapid assessment of glycoprotein IIb/IIIa blockade with the platelet function analyzer (PFA-100) during percutaneous coronary intervention

Background The platelet function analyzer PFA-100 (Dade Behring, Miami, Fla) evaluates platelet function by determining the time to occlusion of an aperture in a membrane coated with collagen and adenosine diphosphate or epinephrine as whole blood flows under shear stress conditions. Platelet aggregation causes aperture occlusion, and results are reported as closure time (CT). Interindividual variability is observed in the level of platelet inhibition achieved with use of the current abciximab dosing regimen (0.25-mg/kg bolus + 10-μg/min infusion for 12 hours). The relationships between specific levels of platelet inhibition and clinical efficacy and safety have not been fully established. Methods and Results We prospectively studied platelet function in 27 patients receiving abciximab during percutaneous coronary intervention. This evaluation included determinations of platelet-rich plasma aggregometry, receptor occupancy studies (D3 assay), and CT measurements at baseline and 10 minutes, 4 hours, 12 hours, and 24 hours after the bolus. All patients received abciximab, aspirin, and heparin; patients undergoing coronary stent implantation received aspirin and ticlopidine after the procedure. CT results were reported within 10 minutes after initiation of testing. For 96% of patients, CT was 300 seconds (maximum CT) immediately after abciximab bolus and remained so throughout the infusion. At 24 hours we observed variable recovery from platelet inhibition and in 72% of patients CT returned to normal (≤130 seconds). Conclusions Findings with the PFA-100 were similar to results observed with platelet aggregometry and receptor occupancy measurements. Most patients treated with abciximab exhibit normalized platelet function at 24 hours despite moderate levels of receptor occupancy, suggesting dissociation between occupancy and function. (Am Heart J 2001;141:226-33.)

Evaluation of primary hemostasis in neonates with a new in vitro platelet function analyzer

With the use of the PFA-100 platelet function analyzer to evaluate primary hemostasis in whole blood, measured as closure time (CT), neonates had shorter CTs than members of an adult control group. Multivariate analysis of measures that contribute to primary hemostasis showed that higher hematocrits and increased ristocetin cofactor activity were the best correlates for CTs of cord blood. These 2 factors may also enhance primary hemostasis in vivo and compensate for the impaired platelet function of the newborn. (J Pediatr 2001;138:116-9)

Monitoring of Aspirin (ASA) Pharmacodynamics with the Platelet Function Analyzer PFA-100®

Anti-platelet drug therapy is currently performed without monitoring, because the established method of platelet aggregometry is cumbersome. The recently developed platelet function analyzer PFA-100 measures shear stress dependent, collagen epinephrine (CEPI) and collagen adenosine diphosphate (CADP) induced platelet plug formation. As the PFA-100 provides a valuable tool to detect patients with platelet dysfunction more efficiently and cost-effectively than aggregometry, we investigated its potential to monitor the efficacy of aspirin treatment. All healthy volunteers (n = 10) received a fractionated infusion of L-aspirin to establish individual dose-response curves. Further, in a randomized, double-blind, placebo controlled two-way cross over study the same volunteers received either 50 or 100 mg aspirin/day p.o. for a period of 11 days to determine the day-to-day variability CEPI induced closure time (CT) under constant intake of low dose aspirin, and to compare the efficacy of those two doses. Intra- and intersubject variability of CEPI-CT averaged 9% and 22%, respectively. Seven volunteers exceeded the maximum of CEPI-CT (>300 s) already after infusion of 100 mg L-aspirin. Intake of 100 mg of aspirin elicited a more rapid onset of effect than 50 mg, which was only significant on days 3 and 4 of aspirin intake. The aspirin induced CEPI-CT prolongation correlated positively with basal CEPI-CT values (r = 0.86; p = 0.001) and were strongly dependent on von Willebrand Factor levels (r = -0.9; p = 0.001). Thus, the PFA-100 system appears suitable to demonstrate an aspirin-induced platelet effect in a longitudinal study, and may be adequate to monitor a patient's compliance. However, prospective trials have to be conducted to demonstrate whether the EPI-CT achieved under ASA-intake has predictive value for cardiovascular outcome.

The relationship between the onset of labor mechanisms and the hemostatic system

The relationship between onset of labor and the hemostatic system was evaluated in 38 pregnant women. The hemostatic system consists of blood coagulation, kinin–kallikrein system, the fibrinolytic system, and platelet function. The most prominent changes take place in the kinin–kallikrein system. After the onset of labor, prekallikrein decreases rapidly which may trigger changes in blood coagulation and the fibrinolytic system. Platelet hemostatic capacity (PHC) was also measured using the PFA-100 (platelet function analyzer) system. Closure times (CT) were shorter during pregnancy, compared to non-pregnant controls, suggesting an increase in PHC. Platelet aggregation by ADP at the end of pregnancy was decreased at the onset of labor. At the same time a slight increase in FDP (fibrin degeneration product) was also seen. While FDP increased, platelet aggregation decreased, which seems to suggest FDP inhibits platelet aggregation. In this manner, these three systems(kinin–kallikrein system, blood coagulation, and fibrinolytic system) and platelet aggregation are closely interrelated, possibly affecting uterine contractility during pregnancy and the onset of labor.

Performance of the platelet function analyser PFA-100 in testing abnormalities of primary haemostasis.

The PFA-100 device is a new instrument for the in-vitro testing of platelet function. Primary haemostasis is stimulated by recording the closure time taken for platelets to seal a 150 microm aperture in the centre of a membrane coated with collagen and either epinephrine or ADP. Patients with type 3 von Willebrand's disease (n = 4) all had infinitely prolonged closure times (> 200 s) with both types of cartridge. A patient with afibrinogenemia exhibited only slightly prolonged closure times of 111 and 166 s for the ADP and epinephrine membranes, respectively. Patients with Glanzmann's thrombasthenia (n = 6) and Bernard Soulier syndrome (n = 2) had grossly prolonged closure times (> 200 s) with both types of cartridges. These results confirmed that the PFA-100 system was highly dependent on normal von Willebrand factor, glycoprotein Ib and glycoprotein IIb/IIIa levels but not on plasma fibrinogen. Patients with storage pool disease (n = 6) and Hermansky Pudlak syndrome (n = 7) had prolonged closure times with the epinephrine cartridge. There was no evidence of enhanced platelet function in patients with antiphospholipid syndrome, in sickle-cell disease or thalassemia. However, ingestion of aspirin resulted in a near consistent and significant prolongation of the closure time for the epinephrine cartridge but not for the ADP cartridge in both normal subjects and patients. The test offers a reliable, reproducible, rapid and simple means of assessing high-shear platelet function in vitro.

213 Detection of impaired platelet function during thrombolysis by PFA-100 platelet function analyzer

213 Detection of impaired platelet function during thrombolysis by PFA-100 platelet function analyzer

Screening for von Willebrand Disease With a New Analyzer Using High Shear Stress: A Study of 60 Cases

AbstractWe have evaluated the performance of a new analyzer using high shear stress, the PFA-100 (Platelet Function Analyzer, Dade International, Massy, France), for screening of patients with von Willebrand disease (vWD). Whole citrated blood is aspirated through a capillary to the central aperture of a membrane coated with collagen and with a platelet agonist (either epinephrine or adenosine diphosphate [ADP]). The time required to obtain occlusion of the aperture by a platelet plug is defined as the closure time (CT). We studied 60 patients with different types of vWD and 96 normal subjects. Fourteen subjects with hemophilia and 15 patients with a platelet disorder were also analyzed. When omitting results from two patients with type 2N, the 58 other patients with type 1, type 2A, type 2B, type 3, or acquired vWD all exhibited an abnormal occlusion with collagen-ADP (sensitivity, 100%) and 56 of 58 had an abnormal CT with collagen-epinephrine (sensitivity, 96.5%). Only two patients with mild type 1 were not detected with collagen-epinephrine. In comparison, the bleeding time (BT) was normal in 20 patients: 17 with type 1, two with type 2A, and one with acquired vWD (sensitivity, 65.5%). The specificity of the PFA-100 was over 95% with both types of cartridges. Thus, the analyzer is well adapted to routine testing, as it has the advantages of simplicity and ease of execution, and demonstrates a high sensitivity, clearly superior to that of BT, for the screening of patients with vWD.