Jun Teruya

Antiplatelet Effect of Aspirin in Patients With Cerebrovascular Disease

Background and Purpose— Aspirin is used commonly to prevent ischemic strokes and other vascular events. Although aspirin is considered safe and effective, it has limited efficacy with a relative risk reduction of 20% to 25% for ischemic stroke. We sought to determine if aspirin as currently used is having its desired antiplatelet effects. Methods— We ascertained patients with cerebrovascular disease who were taking only aspirin as an antiplatelet agent. Platelet function was evaluated using a platelet function analyzer (PFA-100). PFA test results were correlated with aspirin dose, formulation, and basic demographic factors. Results— We ascertained 129 patients, of whom 32% were taking an enteric-coated aspirin preparation and 32% were taking low-dose (≤162 mg/d) aspirin. For the entire cohort, 37% of patients had normal PFA-100 results, indicating normal platelet function. For the patients taking low-dose aspirin, 56% had normal PFAs compared with 28% of those taking ≥325 mg/d of aspirin, while 65% of patients taking enteric-coated aspirin had normal PFAs compared with 25% taking an uncoated preparation (P <0.01 for both comparisons). Similar results were obtained if PFA results were analyzed using mean closure times (low-dose aspirin, 183 sec; high-dose aspirin, 233 sec; enteric-coated, 173 sec; uncoated, 235 sec; P <0.01 for comparisons). Older patients and women were less likely to have a therapeutic response to aspirin, independent of aspirin dose or formulation. Conclusions— A significant proportion of patients taking low-dose aspirin or enteric-coated aspirin have normal platelet function as measured by the PFA-100 test. If these results correlate with clinical events, they have broad implications in determining how aspirin is used and monitored.

Global Hemostasis Testing Thromboelastography: Old Technology, New Applications

Thromboelastography (TEG) as a method of assessing global hemostatic and fibrinolytic function has existed for more than 60 years. Improvements in TEG technology have led to increased reliability and thus increased usage. The TEG has been used primarily in the settings of liver transplant and cardiac surgery, with proven utility for monitoring hemostatic and fibrinolytic derangements. In recent years, indications for TEG testing have expanded to include managing extracorporeal membrane oxygenation (ECMO) therapy, assessing bleeding of unclear etiology, and assessing hypercoagulable states. In addition, TEG platelet mapping has been utilized to monitor antiplatelet therapy. Correlation between TEG platelet mapping and other platelet function tests such as the PFA-100 or platelet aggregation studies, however, has not been evaluated fully for clinical outcomes, and results may not be comparable. In general, the advantages of the TEG include evaluation of global hemostatic function using whole blood, a quick turn-around-time, the possibility of both point-of-care-testing and performance in central laboratories, the ability to detect hyperfibrinolysis, monitoring therapy with recombinant activated factor VII, and detection of low factor XIII activity. Potential applications include polycythemia and dysfibrinogenemia. Disadvantages of TEG include a relatively high coefficient of variation, poorly standardized methodologies, and limitations on specimen stability of native whole blood samples. In the pediatric setting, an additional advantage of the TEG is a relatively small sample volume, but a disadvantage is the difference in normal ranges between infants, especially newborns, and adults. In summary, TEG is an old concept with new applications that may provide a unique perspective on global hemostasis in various clinical settings.

Parameters of Thromboelastography in Healthy Newborns

Thromboelastography (TEG) aids in monitoring a patients global hemostatic system by measuring the rate of clot formation, clot strength, and stability. The usefulness of TEG in pediatric settings, especially with neonates, is limited owing to a lack of neonatal reference values. In this study, neonatal TEG reference intervals were developed and results correlated with other coagulation test parameters. Samples were from women who delivered a neonate after at least 34 weeks of gestation in normal pregnancies. From the recovered placenta, cord blood from the umbilical vein or artery was collected within 30 minutes after delivery and tested. Neonatal TEG reaction time (time clot formation begins), clot firmness (shear elastic modulus strength), and platelet function analysis closure times were significantly lower than those in adult ranges (P< .001). When compared with the values for children, TEG reaction time, angle, coagulation index, clot firmness value, and clot kinetics (time from clot formation to time amplitude reaches 20 mm) were significantly different (P< .001) among neonates. TEG can be used to interpret the data for newborns by using reference values obtained in the present study.

Evaluation of Heparin Assay for Coagulation Management in Newborns Undergoing ECMO

The objective was to identify the usefulness of heparin level by anti-factor Xa (anti-Xa) assay vs activated partial thromboplastin time (PTT) or activated clotting time (ACT) in neonates undergoing extracorporeal membrane oxygenation (ECMO). A retrospective record review of 21 patients in the neonatal intensive care unit (mean ECMO initiation age, 2 days; range, 0-4 days; male/female ratio, 1:1) undergoing ECMO from 2006 to 2008 was performed. Linear regression correlations between anti-Xa, PTT, and ACT were determined by extrapolating PTT and ACT therapeutic ranges that corresponded with the ECMO heparin target range of 0.3 to 0.6 U/mL. Pearson correlation coefficients between heparin levels and PTT (-0.903 to 0.984), PTT less than 40 seconds after correction using PTT-heparinase (-0.903 to 1.000), and ACT (-0.951 to 0.891) in this patient population were widely variable. Inconsistency of PTT and ACT therapeutic ranges corresponding to heparin levels of 0.3 to 0.6 U/mL prompts a multifactorial approach to ECMO management because no single laboratory test can be used to determine appropriate anticoagulation management.

Lupus Anticoagulant Assays: Questions Answered and to Be Answered

CONTEXT Lupus anticoagulants are antibodies with heterogenous specificities to phospholipids. They have been associated with clinical syndromes consisting of thrombosis and recurrent fetal loss. OBJECTIVE To address questions about the laboratory assay aspects of lupus anticoagulants. This review is intended for clinicians managing lupus anticoagulant testing in clinical laboratories. DATA SOURCES Published literature on lupus anticoagulants, with emphasis on laboratory assay methods. CONCLUSIONS Although there are published criteria for confirming the presence of a lupus anticoagulant, there is no consensus on assay methods for lupus anticoagulant testing. The mixing study is a useful screening test for lupus anticoagulants, but it may have limited utility. Clinical context may necessitate the performance of factor assays in addition to lupus anticoagulant testing to rule out factor deficiency or factor-specific inhibitor. Additionally, the presence of different anticoagulants may affect the reliability of lupus anticoagulant assays. Lupus anticoagulants are an independent risk factor for thrombosis. It may be useful to use different assays when there is clinical suspicion for a lupus anticoagulant. When testing for lupus anticoagulants, clinicians must carefully consider the clinical context because factor assays may also be indicated.

Free hemoglobin increases von Willebrand factor-mediated platelet adhesion in vitro: implications for circulatory devices.

Intravascular hemolysis occurs in patients on extracorporeal membrane oxygenation. High levels of free acellular adult hemoglobin (free HbA) are associated with clotting in this mechanical device that can result in thrombotic complications. Adsorption of fibrinogen onto the surface of biomaterial correlates with platelet adhesion, which is mediated by von Willebrand factor (VWF). Because free Hb interacts with VWF, we studied the effect of hemoglobin (Hb) on platelet adhesion to fibrin(ogen) under conditions of different hydrodynamic forces. This effect was investigated using purified human HbA and fibrinogen, extracellular matrix, collagen, or purified plasma VWF as surface-coated substrates to examine flow-dependent platelet adhesion. Antibodies and VWF-deficient plasma were also used. Free Hb (≥50 mg/dL) effectively augmented platelet adhesion, and microthrombi formation on fibrin(ogen), extracellular matrix, and collagen at high shear stress. The effect of free Hb was effectively blocked by anti-glycoprotein Ibα (GPIbα) antibodies or depletion of VWF. Unexpectedly, free Hb also promoted firm platelet adhesion and stable microthrombi on VWF. Lastly, we determined that Hb interacts directly with the A1 domain. This study is the first to demonstrate that extracellular Hb directly affects the GPIbα-VWF interaction in thrombosis, and describes another mechanism by which hemolysis is connected to thrombotic events.

Red cell exchange does not appear to increase the rate of allo- and auto-immunization in chronically transfused children with sickle cell disease.

Allo‐ and auto‐antibody development is a well recognized complication of chronic red cell transfusion (RCT) in sickle cell disease (SCD). Limited matching of Rh (C, c, D, E, e) and K red cell antigens reduces the incidence of immunization.

Bioengineered Factor IX Molecules with Increased Catalytic Activity Improve the Therapeutic Index of Gene Therapy Vectors for Hemophilia B

Although the desire to develop gene therapy for hemophilia B is high, safety remains a concern. Therefore, improving the therapeutic index of gene therapy vectors is an important goal. Thus, we evaluated the use of three bioengineered factor IX (FIX) variants with improved catalytic activity in the context of the helper-dependent adenoviral vector. The first vector expressed R338A-FIX, an FIX variant with the arginine at position 338 changed to an alanine, which resulted in a 2.9-fold higher specific activity (IU/mg) compared with the wild-type FIX. The second vector expressed FIX(VIIEGF1), a variant with the EGF-1 domain replaced with the EGF-1 domain from FVII, which resulted in a 3.4-fold increase in specific activity. The third expressed R338A + FIX(VIIEGF1), a novel variant containing both aforementioned modifications, which resulted in a 12.6-fold increase in specific activity. High-level, long-term, and stable expression of these three variants was observed in hemophilia B mice with no evidence of increased thrombogenicity compared with wild-type FIX. Thus, these bioengineered FIX variants can increase the therapeutic index of gene therapy vectors by permitting administration of lower doses to achieve the same therapeutic outcome. Furthermore, these variants may also be valuable for recombinant FIX protein replacement therapy.

Coinfection with Staphylococcus aureus increases risk of severe coagulopathy in critically ill children with influenza A (H1N1) virus infection.

Objectives:H1N1 influenza with coinfections has been implicated to have high morbidity and mortality. We hypothesized that critically ill children with 2009 H1N1 and coinfections are at a higher risk of developing disseminated intravascular coagulation. Design:The chart review included demographics, length-of-stay, severity of illness score (Pediatric Risk of Mortality III acute physiology score), clinical laboratories, and outcomes at hospital day 90 data. Patients were classified as having methicillin-sensitive or -resistant Staphylococcus aureus, other, or no coinfections. Setting:Single-center pediatric intensive care unit. Patients:Sixty-six consecutive patients with 2009 H1N1 and influenza A infection. Interventions:None. Main Results:There were 12, 22, and 32 patients with methicillin-sensitive or -resistant Staphylococcus aureus, other, and no coinfections, respectively. Pediatric critical care unit length-of-stay was 11, 10, and 5.5 days (median), and survival at day 90 was 83%, 96%, and 91% in patients with methicillin-sensitive or -resistant Staphylococcus aureus, other, and no coinfections. Patients with methicillin-sensitive or -resistant Staphylococcus aureus coinfections compared to patients with other, and no coinfections had higher Pediatric Risk of Mortality III acute physiology scores (14 [6–25] vs. 7 [2–10], p = .052 and 6 [2.5–10], p = .008; median [interquartile range]), higher D-dimer (16.1 [7.9–19.3] vs. 1.6 [1.1–4], p = .02 and 2.3 [0.8–8.7] µg/mL, p = .05), longer prothrombin time (19.3 [15.4–25.9] vs. 15.3 [14.8–17.1], p = .04 and 16.6 [14.7–20.4] secs, p < .39) at admission, and lower day-7 platelet counts (90K [26–161K] vs. 277K [98–314], p = .03 and 256K [152–339]/mm3, p < .07). Patients with methicillin-sensitive or -resistant Staphylococcus aureus coinfections compared to patients without coinfections were more likely to be sicker with Pediatric Risk of Mortality III acute physiology score >10 vs. <10 (relative risk 2.4; 95% confidence interval 1.2–4.7; p = .035) and have overt disseminated intravascular coagulation (relative risk 4.4; 95% confidence interval 1.3–15.8, p = .025). Conclusions:During the 2009–2010 H1N1 pandemic, pediatric patients with influenza A and methicillin-sensitive or -resistant Staphylococcus aureus coinfections were sicker and more likely to develop disseminated intravascular coagulation than patients with other or no coinfections.

A practical approach to pediatric patients referred with an abnormal coagulation profile.

CONTEXT Workup for prolonged prothrombin time (PT) and activated partial thromboplastin time (PTT) is a frequent referral to a Hematology and Coagulation Laboratory. Although the workup should be performed in a timely and cost-effective manner, the complete laboratory assessment of the coagulation state has not been standardized. OBJECTIVE To determine which clinical and laboratory data are most predictive of a coagulopathy and to formulate the most efficient strategy to reach a diagnosis in patients referred for abnormal coagulation profiles. DESIGN Retrospective case review. Medical records of 251 patients referred for prolonged PT and/or PTT to our Hematology Service between June 1995 and December 2002 were reviewed. RESULTS The study included 135 males and 116 females with a mean age of 7.0 years. A personal history of bleeding was reported in 137 patients, and a family history of bleeding was reported in 116 patients. Fifty-one patients (20%) had a coagulopathy (ie, a bleeding risk). Factors predictive of a bleeding risk were a positive family history of bleeding (P < .001) and a positive personal history of bleeding (P = .001). Of 170 patients with findings of normal PT and PTT values on repeat testing, 14 were subsequently diagnosed with a coagulopathy. Two of these patients reported no positive personal or family history of bleeding. CONCLUSIONS Coagulopathy was identified in 20% of the children referred for abnormal PT and/or PTT. In the absence of a personal or family history of bleeding, a normal PT and/or PTT on repeat testing has a negative predictive value of more than 95%.