Platelet-related Hemostasis Research Articles

PFA-100 System: A New Method for Assessment of Platelet Dysfunction.

This is a celebratory reprint of a historical paper published in STH in 1998. The original Abstract follows.The PFA-100 system is a platelet function analyzer designed to measure platelet-related primary hemostasis. The instrument uses two disposable cartridges: a collagen/epinephrine (CEPI) and a collagen/ADP (CADP) cartridge. Previous experience has shown that CEPI cartridges detect qualitative platelet defects, including acetylsalicylic acid (ASA)-induced abnormalities, while CADP cartridges detect only thrombocytopathies and not ASA use. In this seven-center trial, 206 healthy subjects and 176 persons with various platelet-related defects, including 127 ASA users, were studied. The platelet function status was determined by a platelet function test panel. Comparisons were made as to how well the defects were identified by the PFA-100 system and by platelet aggregometry. The reference intervals for both cartridges, testing the 206 healthy subjects, were similar to values described in smaller studies in the literature (mean closure time [CT] of 132 seconds for CEPI and 93 seconds for CADP). The use of different lot numbers of cartridges or duplicate versus singleton testing revealed no differences. Compared with the platelet function status, the PFA-100 system had a clinical sensitivity of 94.9% and a specificity of 88.8%. For aggregometry, a sensitivity of 94.3% and a specificity of 88.3% were obtained. These values are based on all 382 specimens. A separate analysis of sensitivity by type of platelet defect, ASA use versus congenital thrombocytopathies, revealed for the PFA-100 system a 94.5% sensitivity in identifying ASA users and a 95.9% sensitivity in identifying the other defects. For aggregometry, the values were 100% for ASA users and 79.6% for congenital defects. Analysis of concordance between the PFA-100 system and aggregometry revealed no difference in clinical sensitivity and specificity between the systems (p > 0.9999). The overall agreement was 87.5%, with a Kappa index of 0.751. The two tests are thus equivalent in their ability to identify normal and abnormal platelet defects. Testing 126 subjects who took 325 mg ASA revealed that the PFA-100 system (CEPI) was able to detect 71.7% of ASA-induced defects with a positive predictive value of 97.8%. The overall clinical accuracy of the system, calculated from the area under the receiver operating characteristic curve, was 0.977. The data suggest that the PFA-100 system is highly accurate in discriminating normal from abnormal platelet function. The ease of operation of the instrument makes it a useful tool to use in screening patients for platelet-related hemostasis defects.

Primary hemostasis in fetal growth restricted neonates studied via PFA-100 in cord blood samples.

BackgroundPlatelet function of fetal growth restricted (FGR) neonates remains a field of debate. Platelet function analyzer (PFA-100) offers a quantitative in vitro assessment of primary, platelet-related hemostasis. Our aim was to examine platelet function using PFA-100 in FGR neonates and associate our results with perinatal parameters.MethodsPFA-100 was applied on 74 FGR neonates, 48 full-term (>37 weeks' gestation) and 26 preterm neonates (<37 weeks). The control group consisted of 118 healthy neonates. Two closure times (CTs) with COL/EPI and COL/ADP cartridges were determined on cord blood samples for each subject. Statistical analysis was performed by SAS 9.4. The statistical significance level was set at 0.05 and all tests were two-tailed.ResultsCOL/EPI CTs were prolonged in FGR (median 132 s, IQR 95–181 s) compared with control neonates (median 112.5 s, IQR 93–145 s), p = 0.04. Median COL/EPI CT for term and preterm FGR neonates was 126 s (IQR 90–157 s) and 137 s (IQR 104–203), respectively (p = 0.001), and COL/ADP CT was 70 s (IQR 62–80 s) for term and 75 s (IQR 68–82 s) for preterm FGR neonates (p = 0.08). Among FGR neonates, COL/EPI CT was related with delivery time (with preterm neonates exhibiting prolonged COL/EPI CTs), p = 0.05. No correlation was proved between both CTs and hematological parameters in FGR neonates.ConclusionFGR neonates showed impaired platelet function via PFA-100, with preterm FGR neonates confronting the greatest risk. Prolonged COL/EPI CTs in FGR neonates seemed to be independent of hematological parameters and could warn for closer evaluation during the first days of their lives.

Flow cytometry-based platelet function testing is predictive of symptom burden in a cohort of bleeders

Platelet function disorders (PFDs) are common in patients with mild bleeding disorders (MBDs), yet the significance of laboratory findings suggestive of a PFD remain unclear due to the lack of evidence for a clinical correlation between the test results and the patient phenotype. Herein, we present the results from a study evaluating the potential utility of platelet function testing using whole-blood flow cytometry in a cohort of 105 patients undergoing investigation for MBD. Subjects were evaluated with a test panel comprising two different activation markers (fibrinogen binding and P-selectin exposure) and four physiologically relevant platelet agonists (ADP, PAR1-AP, PAR4-AP, and CRP-XL). Abnormal test results were identified by comparison with reference ranges constructed from 24 healthy controls or with the fifth percentile of the entire patient cohort. We found that the abnormal test results are predictive of bleeding symptom severity, and that the greatest predictive strength was achieved using a subset of the panel, comparing measurements of fibrinogen binding after activation with all four agonists with the fifth percentile of the patient cohort (p = 0.00008, hazard ratio 8.7; 95% CI 2.5–40). Our results suggest that whole-blood flow cytometry-based platelet function testing could become a feasible alternative for the investigation of MBDs. We also show that platelet function testing using whole-blood flow cytometry could provide a clinically relevant quantitative assessment of platelet-related hemostasis.

Platelet-Related Hemostasis before and after Hemodialysis with Five Different Anticoagulation Methods

To evaluate platelet-related hemostasis during hemodialysis performed with five different anticoagulation methods. 31 chronic hemodialysis patients, 71% men, aged 57.5 ± 17.4 years, participated in our prospective study. Platelet function analyzer PFA -100 closure time (collagen/epinephrine -CEPI, collagen/adenosine diphosphate -CADP) was measured before and after hemodialysis, which was performed consecutively with five different anticoagulation methods: full-dose unfractionated heparin (UFH) and low-molecular weight heparin (LMWH): 31 patients, regional citrate anticoagulation (RCA): 28 patients, low-dose heparin: 25 patients and "heparin-free'' dialysis: 9 patients. The degree of clotting in the dialysis system was graded on a 5 point scale. CEPI (mean ± SD, reference range 80-160 sec) before vs. after hemodialysis: UFH: 171.7 ± 62.1 vs. 170.8 ± 67.3; LMWH: 167.4 ± 56.9 vs. 159.4 ± 56.4; low-dose heparin: 175.3 ± 69.0 vs. 183.1 ± 60.5; RCA: 172.6 ± 57.4 vs. 161.6 ± 57.0; "heparin-free'': 181.7 ± 56.8 vs. 209.0 ± 66.5; all differences nonsignificant. CADP (mean ± SD, reference range: 68-121 sec) before vs. after hemodialysis: UFH: 132.0 ± 56.6 vs.146.3 ± 68.4; LMWH: 132.4 ± 57,0 vs. 123.1 ± 50.8; low-dose heparin: 137.2 ± 64.2 vs. 143.8 ± 55.5; RCA: 140.7 ± 48.2 vs. 132.9 ± 48.1; "heparin-free'': 137.1 ± 68.0 vs.139.2 ± 29.7; all differences nonsignificant. Before hemodialysis procedure CEPI was increased in 51.2% and CADP in 48.4% of the patients. The best dialysis system clotting score was found with UFH, LMWH and RCA. Platelet dysfunction was demonstrated in approximately half of the chronic hemodialysis patients and was not improved after hemodialysis, regardless of the anticoagulation regimen used.

Could Iron Deficiency Also Affect Platelet‐Related Hemostasis Impairment in Hemodialysis Patients?: Reply

Therapeutic Apheresis and DialysisVolume 15, Issue 4 p. 418-419 Could Iron Deficiency Also Affect Platelet-Related Hemostasis Impairment in Hemodialysis Patients?: Reply Irena Zupan, Irena Zupan Department of Hematology, University Medical Centre, Ljubljana, Slovenia, [email protected]Search for more papers by this authorMiso Sabovic, Miso Sabovic Department of Hematology, University Medical Centre, Ljubljana, Slovenia, [email protected]Search for more papers by this authorBarbara Salobir, Barbara Salobir Department of Hematology, University Medical Centre, Ljubljana, Slovenia, [email protected]Search for more papers by this authorJadranka Buturović-Ponikvar, Jadranka Buturović-Ponikvar Department of Hematology, University Medical Centre, Ljubljana, Slovenia, [email protected]Search for more papers by this authorPeter Cernelc, Peter Cernelc Department of Hematology, University Medical Centre, Ljubljana, Slovenia, [email protected]Search for more papers by this authorJanez Lavre, Janez Lavre Department of Hematology, University Medical Centre, Ljubljana, Slovenia, [email protected]Search for more papers by this authorBojan Vujkovac, Bojan Vujkovac Department of Hematology, University Medical Centre, Ljubljana, Slovenia, [email protected]Search for more papers by this author Irena Zupan, Irena Zupan Department of Hematology, University Medical Centre, Ljubljana, Slovenia, [email protected]Search for more papers by this authorMiso Sabovic, Miso Sabovic Department of Hematology, University Medical Centre, Ljubljana, Slovenia, [email protected]Search for more papers by this authorBarbara Salobir, Barbara Salobir Department of Hematology, University Medical Centre, Ljubljana, Slovenia, [email protected]Search for more papers by this authorJadranka Buturović-Ponikvar, Jadranka Buturović-Ponikvar Department of Hematology, University Medical Centre, Ljubljana, Slovenia, [email protected]Search for more papers by this authorPeter Cernelc, Peter Cernelc Department of Hematology, University Medical Centre, Ljubljana, Slovenia, [email protected]Search for more papers by this authorJanez Lavre, Janez Lavre Department of Hematology, University Medical Centre, Ljubljana, Slovenia, [email protected]Search for more papers by this authorBojan Vujkovac, Bojan Vujkovac Department of Hematology, University Medical Centre, Ljubljana, Slovenia, [email protected]Search for more papers by this author First published: 24 August 2011 https://doi.org/10.1111/j.1744-9987.2011.00991.xRead the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume15, Issue4August 2011Pages 418-419 RelatedInformation

Could Iron Deficiency Also Affect Platelet‐Related Hemostasis Impairment in Hemodialysis Patients?

time) and iron deficiency (measured by hypochromic red cells) in hemodialysis patients, and which speculated that the hemostasis impairment might affect (functional) iron deficiency, most likely by facilitating excessive blood loss (1). This explanation is plausible, but we would like to say that iron deficiency itself could also affect platelet-related hemostasis impairment. Although not as yet extensively studied, Caliskan et al. showed that collagenor adenosine diphosphate-induced platelet aggregation was decreased in patients with iron deficiency anemia (2), and Pati et al. also demonstrated that the rate and degree of platelet aggregation with all agonists (except the lowest concentration of adenosine diphosphate) were significantly lower in anemic patients than in control and post-iron therapy subjects (P < 0.05–0.001) (3). Although it has been reported that uremic patients have decreased shear-induced platelet aggregation mediated by the decreased availability of glycoprotein IIb-IIIa receptors (4), and defective platelet aggregation in uremia is transiently worsened by hemodialysis (5), iron deficiency itself might also cause additional platelet-related hemostasis impairment in hemodialysis patients. However, further studies will be necessary to evaluate whether iron therapy could reverse defective platelet aggregation due to iron deficiency or reduce excessive blood loss in hemodialysis patients in the future.

Exercise-Induced Hemostatic Alterations Are Detectable by Rotation Thrombelastography (ROTEM): A Marathon Study

Rotation thrombelastography (ROTEM) provides a whole blood assay that allows the assessment of plasmic- and platelet-related hemostasis in a single-step procedure. In our current study, we focused on the capability of the method to detect hemostatic alterations induced by physical exercise, enrolling 33 healthy participants of the Dusseldorf Marathon 2006. Venous blood drawn immediately before and after finishing the marathon was analyzed by a rotational thrombelastograph (Pentapharm, Munich, Germany). On initiation of blood coagulation by recalcification, standard ROTEM parameters were determined. Comparison of the results obtained before and after the physical exercise was performed using the Student t test for paired samples. As a result, the mean clotting time (CT) determined from blood samples obtained immediately after the marathon was significantly shorter (662.9 + or - 67.8 seconds vs 505.6 + or - 97.3 seconds, P = .002) and the mean maximal clot firmness was significantly broader (48.4 +/- 6.6 mm vs 51.5 +/- 4.5 mm, P = .0004) when compared to results obtained before the physical exercise. Differences between mean clot formation times (CFTs; 280.6 + 96 seconds vs 270.4 + or - 73.8 seconds) and mean alpha angles (45.9 degrees + or - 8 degrees vs 47.8 degrees + or - 5.8 degrees ) before and after the marathon were not statistically significant. Remarkably, some participants showed opposed results, particularly prolongation of CT and narrowing of maximum clot firmness (MCF). Our study demonstrates that ROTEM is sensitive to exercise-induced hemostatic alterations. The method appears to be capable of detecting even distinct changes in hemostasis in a single-step procedure. Further analyses are needed to clarify which hemostasis parameters influence ROTEM results and which ROTEM results are independent predictors of exercise-induced alterations of plasmic and platelet function. This might help to explain interindividual differences in exercise-induced alterations of hemostasis.

The role of cellular microparticles in platelet-related hemostasis measured using Platelet Function Analyzer-100

Department of Laboratory Medicine, Seoul National University College of Medicine, Seoul, Korea Correspondence to Han-Ik Cho, MD, Department of Laboratory Medicine, Seoul National University College of Medicine, Seoul National University Hospital, 28, Yongon-dong, Chongno-gu, Seoul 110-744, Republic of Korea Tel: +82 2 920 2542; fax: +82 2 3672 8697; e-mail: [email protected]

Expression of Platelet Surface Receptors and Early Changes in Platelet Function in Patients with STEMI Treated with Abciximab and Clopidogrel versus Clopidogrel Alone

Platelets play a crucial role in the pathogenesis of acute coronary syndromes (ACS). The efficacy of antiplatelet treatment is pivotal in the success of percutaneous coronary intervention (PCI) performed in patients with ACS. The aim of the study was to investigate the effects of clopidogrel with or without abciximab on the expression of platelet surface receptors and platelet function in patients with ST-segment elevation myocardial infarction (STEMI) undergoing PCI. Thirty patients with STEMI were included in the study. During acute primary coronary intervention, patients received aspirin (acetylsalicylic acid) and clopidogrel in a loading dose of 300mg. Clopidogrel was the only antiplatelet therapy used by nine patients (group B). Twenty-one patients (group A) received additional abciximab. Blood samples were collected and analyzed twice: before and up to 22 hours after administration of antiplatelet therapy. The platelet aggregation was established as primary platelet-related hemostasis (closure time [CT] assessed using the PFA100 system). The absolute number of platelet surface antigens as CD41a, CD42a, CD42b, CD61, and CD62P were determined by flow cytometry analysis. The study revealed a statistically significant increase in CT induced by adenosine diphosphate and adrenaline (epinephrine) +130 seconds (p < 0.0001) and +94 seconds (p < 0.0001), respectively, in group A patients post-therapy. While in group B the parameters of CT did not change after treatment. In addition, the absolute number of CD41a antigens (glycoprotein [GP] IIb/IIIa) increased significantly after treatment in group A. No significant changes were observed after treatment in the expression of CD62P (P-selectin) antigens in either treatment group. There was a significant reduction in the percentage of CD62P-positive platelets in group B after antiplatelet therapy. The absolute number of GP IIb/IIIa receptors increases and platelets are not activated up to 12 hours after cessation of abciximab therapy. Treatment of STEMI patients undergoing PCI with a loading dose of clopidogrel reduces the percentage of active platelets but does not influence the CT.

Incidence of Aspirin 'Resistance' as Determined Using the PFA-100 in Pediatric Patients with Arterial Ischemic Stroke.

A significant benefit of aspirin (ASA) has been demonstrated in the prevention of arterial thrombotic events in high-risk adult patients. Despite ASA therapy, recurrence of thromboembolic events, or treatment failure, has been reported in 10–20% of patients, and this has been termed ASA 'resistance'. This term has also been applied to the failure of ASA to affect ASA-dependent laboratory tests. As there is little information on ASA 'resistance' in children, we examined the efficacy of ASA treatment on platelets from pediatric stroke patients using the PFA-100. Pediatric arterial ischemic stroke afflicts 2–3 children per 100,000 per year, and is associated with recurrent arterial ischemic stroke or transient ischemic attack in 20–40% of cases. Current treatment includes ASA prophylaxis (3 – 5 mg/kg/day) to inhibit platelet function and prevent recurrence, but it is not known whether this ASA dosing regimen is adequate to inhibit platelet function. Our study population consisted of 95 consecutive children with an index arterial ischemic stroke at mean age 5.9 ± 4.8 yrs (range: 0.1 – 17.0 yrs) on active ASA therapy (2.9 ± 1.2 mg/kg/day). Citrated blood samples were obtained at mean age 9.8 ± 4.8 yrs (range: 0.9 – 19 yrs), and were used to measure primary, platelet-related hemostasis in the high-shear PFA-100 system; closure times (CTs) were determined with the collagen/epinephrine cartridge that is sensitive to ASA's inhibition of thromboxane A2 formation via platelet cyclo-oxygenase 1. The mean CT for all 95 patients was 244 ± 68.1 sec, which is greater than 163 sec, the upper limit of the normal range that we have previously determined for healthy children. The majority of patients, 75/95 (79%), had prolonged CTs (172 sec to > 300 sec), indicating inhibition of platelet function by ASA, and they were thus responsive to ASA therapy. 45 of the 75 ASA responders (63%) had CTs > 300 sec, i.e. CTs greater than the maximum test time of 300 sec, demonstrating aperture non-closure. The remaining 20/95 patients (21%) were ASA 'resistant', as they did not respond to ASA therapy, having CTs (93 – 163 sec) within the normal range. Mean ASA dosage did not differ between ASA responders (2.8 ± 1.2 mg/kg/day) and ASA 'resistant' patients (3.0 ± 1.4 mg/kg/day). 6 of the ASA 'resistant' patients had their ASA dosage increased, and on repeat PFA-100 testing, 5/6 showed increased CTs > 163 sec. In conclusion, in children with arterial ischemic stroke, the majority, 79%, demonstrate inhibition of platelet function, as determined using the PFA-100, by ASA therapy at a mean dose of 2.9 mg/kg/day. The reason for the lack of inhibition of platelet function in 21% of pediatric patients, whether increased ASA dosage or alternative anti-platelet agents (e.g. clopidogrel) should be used in ASA 'resistant' patients, and the relationship between ASA 'resistance' and recurrence of arterial thrombotic events in children require further studies.

Synthesis and antiplatelet activity of thioaryloxyacids analogues of clofibric acid

The thiophene-, benzothiazole- and pyridine-thioaryloxyacids analogues of clofibric acid were synthesized and their antiplatelet activity was screened. Some compounds exhibited antiaggregating properties. The platelet-related haemostasis was measured on a PFA-100® analyzer using bull blood.

High clotting factor activities and enhanced platelet-related haemostasis in a patient with recurrent episodes of thrombotic–thrombocytopenic purpura: additional risk factors for onset and recurrence?

High clotting factor activities and enhanced platelet-related haemostasis in a patient with recurrent episodes of thrombotic–thrombocytopenic purpura: additional risk factors for onset and recurrence?

The hepoxilin stable analogue, PBT-3, inhibits primary, platelet-related hemostasis in whole blood measured in vitro with the PFA-100

Hepoxilins are hydroxy epoxide metabolites of arachidonic acid formed through a coupled reaction involving 12(S)-lipoxygenase and the putative enzyme, hepoxilin synthase, that transforms 12S-HPETE into the hepoxilins (Fig. 1) (see Refs. [1–3] for reviews). Hepoxilins possess a variety of biological actions in vitro as well as in vivo including insulin release from pancreatic islets, potentiation of vascular contraction, blockade of neurotransmitter release, regulation of cell volume and they provoke skin vascular permeability. Because the native hepoxilins are unstable chemically, a new family of stable analogues, PBTs, designed to have chemical and biological stability suitable for in vivo studies, were prepared by total chemical synthesis [4] (Fig. 1). In fact, one of the analogues, PBT-1, potently inhibits lung fibrosis in vivo evoked by bleomycin [5]. Another of the analogues, PBT-3, selectively blocked heparin-primed human platelet aggregation evoked by ADP [6] and inhibited platelet aggregation evoked by collagen with blockade of thromboxane A2 formation [7]. PBT-3 potently antagonized the thromboxane receptor [7].

Xenon does not affect human platelet function in vitro.

We sought to determine whether xenon affects platelet glycoprotein expression and platelet-related hemostasis in vitro at a clinically relevant concentration. Human whole blood was stimulated with either adenosine diphosphate or the thrombin receptor agonist peptide (TRAP)-6 after incubation with 65% xenon. Halothane at 2 minimum alveolar anesthetic concentration was used as a positive control. Platelet function and activation were evaluated with two-color flow cytometry. The expression of the platelet glycoproteins GPIIb/IIIa, GPIb, and P selectin were detected with fluorochrome-conjugated monoclonal antibodies. In vitro measurement of platelet-related hemostasis under conditions of high shear stress was performed in citrated whole blood with a platelet function analyzer (PFA-100((R))) by using collagen/epinephrine and collagen/adenosine diphosphate cartridges. Xenon did not affect basal or agonist-induced expression of platelet membrane glycoproteins, activation-dependent conformational changes of the GPIIb/IIIa receptor, expression of P selectin, or PFA closure times. In contrast, halothane reduced TRAP-6-induced activation of the GPIIb/IIIa complex. Furthermore, collagen/epinephrine-induced PFA closure time was significantly prolonged. These results demonstrate that xenon does not affect the unstimulated or agonist-induced platelet glycoprotein expression, activation of GPIIb/IIIa, or platelet-related hemostasis.

Cocoa inhibits platelet activation and function

Epidemiologic studies have shown inverse associations between dietary polyphenols and mortality from coronary heart disease. However, the basis for this protective association is uncertain. Food polyphenols reportedly have antioxidant properties and decrease platelet function in vitro. This study sought to evaluate whether consumption of a polyphenol-rich cocoa beverage modulates human platelet activation and primary hemostasis. Peripheral blood was obtained from 30 healthy subjects before and 2 and 6 h after ingestion of a cocoa beverage (n = 10), a caffeine-containing control beverage (n = 10), or water (n = 10). Platelet activation was measured in terms of expression of activation-dependent platelet antigens and platelet microparticle formation by using fluorescent-labeled monoclonal antibodies and flow cytometry. Primary platelet-related hemostasis was measured with a platelet function analyzer. Ex vivo epinephrine- or ADP-stimulated expression of the fibrinogen-binding conformation of glycoprotein IIb-IIIa was lower 2 and 6 h after consumption of cocoa than before consumption. Cocoa consumption also decreased ADP-stimulated P-selectin expression. In contrast, epinephrine-induced platelet glycoprotein IIb-IIIa expression increased after consumption of the caffeine-containing beverage but not after water consumption. Platelet microparticle formation decreased 2 and 6 h after cocoa consumption but increased after caffeine and water consumption. Primary hemostasis in response to epinephrine in vitro was inhibited 6 h after cocoa consumption. The caffeine-containing beverage inhibited ADP-induced primary hemostasis 2 and 6 h after consumption. Cocoa consumption suppressed ADP- or epinephrine-stimulated platelet activation and platelet microparticle formation. Cocoa consumption had an aspirin-like effect on primary hemostasis.

Use of the PFA-100 in the assessment of primary, platelet-related hemostasis in a pediatric setting.

The platelet function analyzer, PFA-100, has been designed to provide an in vitro measure of primary hemostasis simply, quickly, quantitatively, and accurately to aid in the routine screening of patients with potential hemorrhagic risk due to abnormal platelet plug formation. The system measures the closure time (CT), or the time taken for platelets in a sample of anticoagulated blood to form a plug that occludes a microscopic aperture cut into a membrane coated with collagen and either epinephrine or ADP. The high shear stresses produced in the analyzer lead to platelet plug formation that is greatly dependent on von Willebrand's factor (vWF). In this article, we detail the system itself and describe our initial studies using the PFA-100 to assess primary hemostasis in pediatric populations. Normal ranges have been established for healthy children and neonates. CTs for healthy children are independent of the needle gauge (21G or 23G) used for blood sampling. They are similar to CTs for healthy adults, but neonates have significantly shorter CTs, likely due to increased levels of vWF. Children with hemophilia have normal CTs, whereas seven out of eight patients with von Willebrand's disease (vWD) have abnormally long CTs. CT reproducibility between duplicate samples is excellent. Our preliminary results indicate that the PFA-100 will be useful in the evaluation of primary hemostasis in children, as well as in adults.

The Platelet Function Analyzer (PFA-100): a novel in-vitro system for evaluation of primary haemostasis in children.

The PFA-100 system provides an in-vitro method of assessing primary platelet-related haemostasis by measuring the time (the closure time, or CT) taken for a platelet plug to occlude a microscopic aperture cut into a membrane coated with collagen and either epinephrine or ADP. We used the system to establish normal ranges for CTs in healthy children, adults and neonates. Mean CTs of healthy children were independent of the needle gauge used (21G or 23CG) for blood sampling; they were very similar to the mean CTs of healthy adults, but longer than mean CTs of healthy neonates. Although children with haemophilia had normal CTs, the PFA-100 system was found to be potentially useful in screening for von Willebrand disease in children.

Preliminary data from a field trial of the PFA-100 system.

The PFA-100 system (Dade International Inc., Miami, FL) is a platelet function analyzer, the design of which is based on the technology of the Thrombostat 4000 VDG, Seeon, Germany. It was developed to measure primary, platelet dependent hemostasis in citrated whole blood in vitro. A first pilot study was conducted with the instrument to assess performance characteristics. Healthy subjects (normals) who had not ingested any medications, and patients (abnormals) with primary, platelet-related hemostasis defects, which included users of aspirin, were studied with two test cartridges; collagen/ADP and collagen/epinephrine. Before the study certain variables were tested that ascertained that blood drawn into either 3.8% or 3.2% sodium citrate containing vacutainers (rather than syringes) could be used for testing. Tests must be performed within a five-hour time span from drawing to testing, and blood must be kept at room temperature. Normal reference values were 77-133 seconds closure times for collagen/ADP and 98-185 seconds for collagen/epinephrine. Precision testing revealed a CV of < 10% for within-day and between-day (five days) analyses on collagen/ADP cartridges and a CV of 5-14% for both runs on the collagen/epinephrine cartridges. No clinically important differences were found between measurements in the two positions of the instrument, although one follows the other.(ABSTRACT TRUNCATED AT 250 WORDS)