Sickle cell trait and the risk of venous thromboembolism among blacks

Hormonal contraception, sickle cell trait, and risk for venous thromboembolism among African American women

OBJECTIVE

We evaluated the effect of oral and other hormonal contraceptive (HC) use on venous thromboembolism risk among African American women and investigated whether the association was modified by the sickle cell trait.

STUDY DESIGN

We report the findings of a case-control study that included 60 African American women with an idiopathic, first episode of venous thromboembolism and 196 African American controls.

RESULTS

The odds of current HC use compared with noncurrent use contrasting cases and controls is 3.8 (95% confidence interval [CI], 1.7-8.1; P < .001). Among subjects with sickle cell trait, the odds ratio is higher (odds ratio [OR], 6.7; 95% CI, 1.0-43) than the odds ratio among subjects without sickle cell trait (OR, 2.6; 95% CI, 1.1-6.2), but the difference is not statistically significant.

CONCLUSION

This study provides persuasive evidence that hormonal contraceptive use increases venous thromboembolism risk among African American women and that the increase in risk may be larger among women with sickle cell trait.

Complications associated with sickle cell trait: a brief narrative review

Sickle cell trait occurs in approximately 300 million people worldwide, with the highest prevalence of approximately 30% to 40% in sub-Saharan Africa. Long considered a benign carrier state with relative protection against severe malaria, sickle cell trait occasionally can be associated with significant morbidity and mortality. Sickle cell trait is exclusively associated with rare but often fatal renal medullary cancer. Current cumulative evidence is convincing for associations with hematuria, renal papillary necrosis, hyposthenuria, splenic infarction, exertional rhabdomyolysis, and exercise-related sudden death. Sickle cell trait is probably associated with complicated hyphema, venous thromboembolic events, fetal loss, neonatal deaths, and preeclampsia, and possibly associated with acute chest syndrome, asymptomatic bacteriuria, and anemia in pregnancy. There is insufficient evidence to suggest an independent association with retinopathy, cholelithiasis, priapism, leg ulcers, liver necrosis, avascular necrosis of the femoral head, and stroke. Despite these associations, the average life span of individuals with sickle cell trait is similar to that of the general population. Nonetheless, given the large number of people with sickle cell trait, it is important that physicians be aware of these associations.

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.

Venous sinus thrombosis leading to stroke in a patient with sickle cell disease on hydroxyurea and high hemoglobin levels: treatment with thrombolysis

A 21-year-old man with homozygous sickle cell disease maintained on hydroxyurea for 1 year developed thrombosis of the superior sagittal, right transverse, and right sigmoid dural sinuses with a large venous infarct. He was successfully treated with endovascular thrombolysis. Investigation did not reveal any inherited or acquired hypercoagulable state. This patient however had consistently elevated hemoglobin levels both at the time of the initial event and on follow up. One year later he developed symptomatic avascular necrosis of the right hip. High hemoglobin levels resulting from hydroxyurea therapy may have contributed to development of complications in this patient.

Effects of strenuous exercise on autonomic nervous system activity in sickle cell trait carriers

This study compared the nocturnal autonomic nervous system (ANS) activity in seven sickle cell trait (SCT) carriers and six subjects with normal hemoglobin in response to exercise Sympathetic and parasympathetic indices of nocturnal ANS were measured in the two groups before and 24 and 48 h after a strenuous exercise consisting of the repetition of three maximal exercise bouts. Global ANS activity decreased 24 h after exercise in both groups and was lower before as well as after exercise in SCT carriers. Indices of parasympathetic activity were lower in SCT carriers at all times, indicating a persistent sympatho-vagal imbalance. Exercise did not cause a rebound in parasympathetic activity in either group, but a rebound was noted for sympathetic index values two days after exercise in SCT group only. The ANS activity was generally lower, and the sympatho-vagal imbalance greater, in SCT carriers compared with control subjects irrespective of exercise and could increase the risk for medical complications in this population.

The role of the hematologist/oncologist in the care of patients with vascular anomalies

Pediatric hematologist/oncologists have a critical role in the diagnosis and management of patients who have complex vascular anomalies. They provide the clinical and medical skills needed to diagnose, treat, and manage these patients. Hematologist/oncologists also provide support for clinical trials and drug development to further treatment options for these patients.

Sickle Cell Trait, Oral Contraceptives, and the Risk of Venous Thromboembolism

We recently reported that sickle-cell trait (SCT) is a risk factor for venous thromboembolism (VTE) among African Americans (1). Since current usage of oral contraceptives (OC’s) is an established risk factor for VTE in women of European descent, we investigated the joint effect of OC’s and SCT on VTE risk in the Genetic Attributes and Thrombosis Epidemiology (GATE) study. This case-control study included 57 African American women with an idiopathic, first deep-vein thrombosis and/or pulmonary embolism and 185 controls between the ages of 18 and 49. Subjects were genotyped at codon 6 (E&gt;V) for the hemoglobin S mutation and were interviewed about OC usage. The distribution of cases and controls according to current OC use and SCT is displayed below: The odds ratio of VTE among OC users versus women not currently using OC’s is 2.7 (95% CI: 1.4, 5.1; P = 0.003). However, among subjects with SCT, the odds ratio for OC use is considerably higher (OR = 7.0; 1.1, 45; P = 0.04) than is the odds ratio for OC use among women without SCT (OR = 2.1; 1.0, 4.3; P = 0.05), although the difference in these two odds ratios is not statistically significant (P &gt; 0.20). Nonetheless, the findings indicate that overall, current OC use is a strong risk factor for VTE among African American women. The observation that there is synergy between current OC use and SCT provides some additional support for the finding that SCT is a risk factor for VTE. However, a limitation of this analysis is small numbers and the resultant imprecision. Replication of these findings is thus required before causation can be established.

Current OC use and Sickle Cell Trait SCT OC Case Control Odds Ratio No No 31 138 1.0 No Yes 15 32 2.1 Yes No 4 12 1.5 Yes Yes 7 3 10.4

Hypercoagulability in Sickle Cell Disease: New Approaches to an Old Problem

Patients with sickle cell disease (SCD) exhibit high plasma levels of markers of thrombin generation, depletion of natural anticoagulant proteins, abnormal activation of the fibrinolytic system, and increased tissue factor expression, even in the non-crisis steady state. In addition, platelets and other cellular elements are chronically activated in the non-crisis state. Despite an abundance of evidence for coagulation and platelet activation, it remains uncertain whether these changes contribute to the pathophysiology of SCD or are, rather, simple epiphenomena. With the occurrence of macrovascular thrombotic complications in SCD, as well as the recognition that soluble CD40 ligand is biologically active in SCD, coagulation and platelet activation may indeed play a role in SCD pathophysiology. Defining a role for hypercoagulability in SCD requires further understanding of its pathogenesis. Furthermore, the conduct of well-controlled clinical trials using anticoagulants and antiplatelet agents and using a variety of clinical endpoints is warranted.