Soheir S Adam

D-dimer antigen: current concepts and future prospects.

The D-dimer antigen is a unique marker of fibrin degradation that is formed by the sequential action of 3 enzymes: thrombin, factor XIIIa, and plasmin. First, thrombin cleaves fibrinogen producing fibrin monomers, which polymerize and serve as a template for factor XIIIa and plasmin formation. Second, thrombin activates plasma factor XIII bound to fibrin polymers to produce the active transglutaminase, factor XIIIa. Factor XIIIa catalyzes the formation of covalent bonds between D-domains in the polymerized fibrin. Finally, plasmin degrades the crosslinked fibrin to release fibrin degradation products and expose the D-dimer antigen. D-dimer antigen can exist on fibrin degradation products derived from soluble fibrin before its incorporation into a fibrin gel, or after the fibrin clot has been degraded by plasmin. The clinical utility of D-dimer measurement has been established in some scenarios, most notably for the exclusion of VTE. This article consists of 2 sections: in the first, the dynamics of D-dimer antigen formation is discussed and an overview of commercially available D-dimer assays is provided. The second section reviews available evidence for the clinical utilization of D-dimer antigen measurement in VTE, as well as emerging areas of D-dimer utilization as a marker of coagulation activation in other clinical settings.

Comparative Effectiveness of Warfarin and New Oral Anticoagulants for the Management of Atrial Fibrillation and Venous Thromboembolism: A Systematic Review

BACKGROUND New oral anticoagulants (NOACs), including direct thrombin inhibitors (DTIs) and factor Xa (FXa) inhibitors, are emerging alternatives for prophylaxis and treatment of atrial fibrillation (AF) and venous thromboembolism (VTE). PURPOSE To compare the benefits and harms of NOACs versus warfarin for AF and VTE. DATA SOURCES MEDLINE, EMBASE, and the Cochrane Database of Systematic Reviews from January 2001 through July 2012; U.S. Food and Drug Administration (FDA) database for adverse event reports. STUDY SELECTION English-language, randomized, controlled trials (RCTs) comparing NOACs with warfarin for management of AF or VTE and observational studies and FDA reports on adverse effects. DATA EXTRACTION Two independent reviewers abstracted data and rated study quality and strength of evidence. DATA SYNTHESIS Six good-quality RCTs compared NOACs (2 DTI studies, 4 FXa inhibitor studies) with warfarin. In AF, NOACs decreased all-cause mortality (risk ratio [RR], 0.88 [95% CI, 0.82 to 0.96]); in VTE, NOACs did not differ for mortality or VTE outcomes. Across indications, adverse effects of NOACs compared with warfarin were fatal bleeding (RR, 0.60 [CI, 0.46 to 0.77]), major bleeding (RR, 0.80 [CI, 0.63 to 1.01]), gastrointestinal bleeding (RR, 1.30 [CI, 0.97 to 1.73]), and discontinuation due to adverse events (RR, 1.23 [CI, 1.05 to 1.44]). Subgroup analyses suggest a higher risk for myocardial infarction with DTIs than with FXa inhibitors. Bleeding risk for NOACs may be increased in persons older than 75 years or those receiving warfarin who have good control. LIMITATION There were no head-to-head comparisons of NOACs and limited data on harms. CONCLUSION New oral anticoagulants are a viable option for patients receiving long-term anticoagulation. Treatment benefits compared with warfarin are small and vary depending on the control achieved by warfarin treatment. PRIMARY FUNDING SOURCE Department of Veterans Affairs.

Comparative Effectiveness of New Oral Anticoagulants and Standard Thromboprophylaxis in Patients Having Total Hip or Knee Replacement: A Systematic Review

BACKGROUND Pharmacologic thromboprophylaxis reduces the risk for venous thromboembolism after total hip replacement (THR) or total knee replacement (TKR). New oral anticoagulants (NOACs), including direct thrombin inhibitors and factor Xa inhibitors, are emerging options for thromboprophylaxis after these procedures. PURPOSE To compare the benefits and risks of NOACs versus standard thromboprophylaxis for adults having THR or TKR. DATA SOURCES MEDLINE, EMBASE, and the Cochrane Database of Systematic Reviews from January 2009 through March 2013. STUDY SELECTION English-language systematic reviews. DATA EXTRACTION Two independent reviewers abstracted data and rated study quality and strength of evidence. DATA SYNTHESIS Six good-quality systematic reviews compared NOACs with low-molecular-weight heparin (LMWH) for thromboprophylaxis after THR or TKR. Risk for symptomatic deep venous thrombosis, but not risk for death or nonfatal pulmonary embolism, was reduced with factor Xa inhibitors compared with LMWH (4 fewer events per 1000 patients). Conversely, the risk for major bleeding increased (2 more events per 1000 patients). Outcomes of dabigatran did not significantly differ from those of LMWH. Indirect evaluation of NOACs by common comparison with LMWH showed nonsignificantly reduced risks for venous thromboembolism with rivaroxaban compared with dabigatran (risk ratio [RR], 0.68 [95% CI, 0.21 to 2.23]) and apixaban (RR, 0.59 [CI, 0.26 to 1.33]) but increased major bleeding. New oral anticoagulants have not been compared with warfarin, aspirin, or unfractionated heparin. LIMITATIONS Head-to-head comparisons among NOACs were not available. Efficacy is uncertain in routine clinical practice. CONCLUSION New oral anticoagulants are effective for thromboprophylaxis after THR and TKR. Their clinical benefits over LMWH are marginal and offset by increased risk for major bleeding. PRIMARY FUNDING SOURCE U.S. Department of Veterans Affairs.

Urinary albumin excretion is associated with pulmonary hypertension in sickle cell disease: potential role of soluble fms-like tyrosine kinase-1.

Background:  Pulmonary hypertension (PHT) is reported to be associated with measures of renal function in patients with sickle cell disease (SCD). The purpose of this exploratory study was to determine the relationship between albuminuria and both clinical and laboratory variables in SCD.

Surgical and Obstetric Outcomes in Adults with Sickle Cell Disease

BACKGROUND Sickle cell disease patients are more likely than the general population to undergo surgery and usually do so at a younger age. Female sickle cell disease patients also have special gynecological and obstetric issues related to their disease. METHODS We collected data through standardized clinical report forms, patient interviews, and medical records from 509 adult sickle cell disease patients. Logistic regression was used to estimate the association between multiple variables and each of the surgery types. We also determined the prevalence and outcomes of pregnancy in 284 women with sickle cell disease in this population. RESULTS Almost 50% of patients aged 18-27 years had had a cholecystectomy. Mean corpuscular hemoglobin, total bilirubin, and lactate dehydrogenase were significantly higher in the postcholecystectomy group; 9.5% of 504 individuals had undergone splenectomy. Hematocrit, body mass index, and red blood cell count were significantly higher in the postsplenectomy group. Hip replacement had been performed in 9.2% of individuals, with the prevalence increasing as early as the fourth decade and continuing to increase through the sixth decade of life. A history of pregnancy was present in 190 women (67%). Of 410 pregnancies, only 53.9% resulted in live births, 16.6% were voluntarily terminated, and 29.5% were complicated by miscarriage, still birth, or ectopic implantation. CONCLUSIONS Sickle cell disease continues to have a strong effect on the mean age for common surgeries and impacts pregnancy outcomes. We conclude that this population has a unique surgical and obstetric history that should be further studied to provide insight into potentially more effective preventive approaches to end-organ damage.

Impact of sickle hemoglobinopathies on pregnancy-related venous thromboembolism

OBJECTIVE The aim of the study is to examine the relationship between sickle cell trait (Hb AS) and other sickle hemoglobinopathies and the risk of thromboembolism during pregnancy or the puerperium. STUDY DESIGN Retrospective cohort study of African American women receiving prenatal care from 1991 to 2006. Sickle cell status was ascertained by routine hemoglobin electrophoresis. Venous thromboembolism (VTE) was defined as one or more episodes of deep venous and/or pulmonary thromboembolism during pregnancy or the puerperium according to discharge diagnoses based on International Classification of Diseases, Ninth Revision codes. RESULTS Among 22,140 women with hemoglobin (Hb) AA status, 20 women (0.09%) experienced pregnancy-related VTE compared with 3 women (0.15%) of 2,037 women with Hb AS; relative risk (RR) for the association with AS status = 1.6; 95% confidence interval (CI) 0.5 to 5.5. Of 103 women, 3 women (2.9%) with sickle cell disease conditions (Hb SS, Hb SC, or Hb S,beta-thalassemia) experienced thromboembolism. Compared with women with Hb AA status, the RR = 32.2, 95% CI 9.7 to 107. CONCLUSION Sickle cell trait may be associated with a modest increase in VTE in the setting of pregnancy; sickle cell disease conditions are strongly associated with this rare but potentially fatal outcome.

Effectiveness of Intermittent Pneumatic Compression Devices for Venous Thromboembolism Prophylaxis in High-Risk Surgical Patients: A Systematic Review

BACKGROUND Thromboprophylaxis regimens include pharmacologic and mechanical options such as intermittent pneumatic compression devices (IPCDs). There are a wide variety of IPCDs available, but it is uncertain if they vary in effectiveness or ease of use. This is a systematic review of the comparative effectiveness of IPCDs for selected outcomes (mortality, venous thromboembolism [VTE], symptomatic or asymptomatic deep vein thrombosis, major bleeding, ease of use, and adherence) in postoperative surgical patients. METHODS We searched MEDLINE (via PubMed), Embase, CINAHL, and Cochrane CENTRAL from January 1, 1995, to October 30, 2014, for randomized controlled trials, as well as relevant observational studies on ease of use and adherence. RESULTS We identified 14 eligible randomized controlled trials (2633 subjects) and 3 eligible observational studies (1724 subjects); most were conducted in joint arthroplasty patients. Intermittent pneumatic compression devices were comparable to anticoagulation for major clinical outcomes (VTE: risk ratio, 1.39; 95% confidence interval, 0.73-2.64). Limited data suggest that concurrent use of anticoagulation with IPCD may lower VTE risk compared with anticoagulation alone, and that IPCD compared with anticoagulation may lower major bleeding risk. Subgroup analyses did not show significant differences by device location, mode of inflation, or risk of bias elements. There were no consistent associations between IPCDs and ease of use or adherence. CONCLUSIONS Intermittent pneumatic compression devices are appropriate for VTE thromboprophylaxis when used in accordance with current clinical guidelines. The current evidence base to guide selection of a specific device or type of device is limited.

Coagulation activation in sickle cell trait: an exploratory study

Recent epidemiologic data suggest that sickle cell trait (HbAS; AS) is a risk factor for venous thromboembolism. We conducted an exploratory study of healthy subjects with AS under baseline conditions to determine whether a chronic basal hyperactivation of coagulation exists, and if so, what mechanism(s) contribute to this state. Eighteen healthy AS individuals were compared to 22 African‐American controls with a normal haemoglobin profile (HbAA; AA) and 17 patients with sickle cell disease (HbSS; SS). Plasma thrombin‐antithrombin complexes and D‐dimer levels were elevated in AS relative to AA patients (P = 0·0385 and P = 0·017, respectively), and as expected, were much higher in SSversusAA (P < 0·0001 for both). Thrombin generation in platelet poor plasma was indistinguishable between AA and AS subjects, whereas a paradoxical decrease in endogenous thrombin potential was observed in SS (P ≤ 0·0001). Whole blood tissue factor was elevated in SS compared to AA (P = 0·005), but did not differ between AA and AS. Plasma microparticle tissue factor activity was non‐significantly elevated in AS (P = 0·051), but was clearly elevated in SS patients (P = 0·004) when compared to AA controls. Further studies in larger cohorts of subjects with sickle cell trait are needed to confirm the results of this preliminary investigation.

Potential role for statins in sickle cell disease

The complex pathophysiology of sickle cell disease (SCD) is remarkably similar to that observed in other chronic vascular diseases and involves multiple biologic pathways triggered by ischemia reperfusion injury, coagulation activation, and inflammation. Statins are potent lipid‐lowering agents commonly used to reduce the risk of cardiovascular disease. Independent of their lipid lowering effect, statins have been shown to down‐regulate inflammatory mediators and endothelial adhesion molecules, reduce tissue factor expression and restore nitric oxide bioavailability. The pleiotropic effects of statins make these agents attractive therapeutic candidates for SCD. This article reviews available evidence for the potential role of statins in SCD. Pediatr Blood Cancer 2013; 60: 550–557.

iPSC modeling of severe aplastic anemia reveals impaired differentiation and telomere shortening in blood progenitors.

Aplastic Anemia (AA) is a bone marrow failure (BMF) disorder, resulting in bone marrow hypocellularity and peripheral pancytopenia. Severe aplastic anemia (SAA) is a subset of AA defined by a more severe phenotype. Although the immunological nature of SAA pathogenesis is widely accepted, there is an increasing recognition of the role of dysfunctional hematopoietic stem cells in the disease phenotype. While pediatric SAA can be attributable to genetic causes, evidence is evolving on previously unrecognized genetic etiologies in a proportion of adults with SAA. Thus, there is an urgent need to better understand the pathophysiology of SAA, which will help to inform the course of disease progression and treatment options. We have derived induced pluripotent stem cell (iPSC) from three unaffected controls and three SAA patients and have shown that this in vitro model mimics two key features of the disease: (1) the failure to maintain telomere length during the reprogramming process and hematopoietic differentiation resulting in SAA-iPSC and iPSC-derived-hematopoietic progenitors with shorter telomeres than controls; (2) the impaired ability of SAA-iPSC-derived hematopoietic progenitors to give rise to erythroid and myeloid cells. While apoptosis and DNA damage response to replicative stress is similar between the control and SAA-iPSC-derived-hematopoietic progenitors, the latter show impaired proliferation which was not restored by eltrombopag, a drug which has been shown to restore hematopoiesis in SAA patients. Together, our data highlight the utility of patient specific iPSC in providing a disease model for SAA and predicting patient responses to various treatment modalities.