Leg ulcers are a serious complication of Sickle Cell Disease (SCD), often linked to a hemolytic phenotype that includes priapism, pulmonary hypertension (PH) and renal disease. In the SCD pathogenesis, hemolysis and ischemia-reperfusion injuries lead to white blood cell (WBC), platelet and endothelial cell activation, pro-inflammatory cytokine production and subsequent activation of coagulation that tips the balance towards a prothrombotic and inflammatory state. Decreased levels of the naturally occurring anticoagulants (NOACs): protein C (PC), protein S (PS), antithrombin III (ATIII), have been observed in patients with SCD in steady state, with some reports stating no differences between steady state and crisis. This occurs due to decreased production, increased consumption, or a combination of both. However, the definite mechanisms have not yet been elucidated. Factor V Leiden (FVL) and prothrombin G20210A mutations are rare in African Americans and in patients with SCD. We speculated that patients with leg ulcers would have a more pronounced pro-thrombotic phenotype than patients who never developed them.
127 adults with and without SCD leg ulcers were evaluated at steady state in the prospective cross-sectional INSIGHTS study - Insights into Microbiome and Environmental Contributions to Sickle Cell Disease and Leg Ulcers (ClinicalTrials.gov Identifier NCT02156102). At the time of enrollment, a clinical examination and a comprehensive past medical history were completed. Routine blood work including a full coagulation profile and analysis of blood clotting genetic mutations (thrombophilia genetic tests) were obtained. Laboratory results were compared between groups with and without leg ulcers using Chi-square or Fisher exact tests. Multivariable logistic regression analysis was conducted to test whether deep venous thrombosis (DVT) and pulmonary embolism (PE), clinical surrogates of a prothrombotic phenotype, were associated with the decreased NOACs (PC, PS), or leg ulcer.
The study cohort consisted of 109 adults with Hb SS, 10 with Hb SC, 5 with Hb S beta thalassemia zero, and 3 with Hb S beta thalassemia plus. Of these, there were 35 subjects with leg ulcers. NOACs were found to be decreased in the sub-group of subjects with leg ulcers. Among those with leg ulcers, 49% had functional PC levels that were below the normal range, compared to 27% of those without leg ulcers (p=0.022) 74% had functional PS levels below the normal range, compared to 51% of study patients without leg ulcers (p=0.018); 23% had AT III levels below the normal range, compared to 17% of SCD patients without leg ulcers (p=0.482); and 29% tested positive for lupus anticoagulant (LA), compared to 25% of SCD patients without leg ulcers (p=0.682). Among the leg ulcer cohort, none of the subjects had the prothrombin gene mutation, while 3 subjects without leg ulcers were heterozygous for it. None of the subjects in our cohort had FVL mutation. The multivariable analysis showed that none of PC, PS, or leg ulcer was significantly associated with either DVT or PE.
In SCD patients with leg ulcers, PC and PS levels are significantly lower than in SCD patients without leg ulcers. Additionally, in SCD patients with leg ulcers, there is a trend towards decreased levels of AT III and increased LA positivity. FVL and prothrombin gene mutations were rare in our cohort, consistent with the general population. The above findings did not correlate clinically with a history of DVT/PE in the same population.
Our results of decreased NOACs confirm previous reports from our group that demonstrated similar findings. Of greater significance, however, is our finding that sickle cell patients with leg ulcers have further decreased levels of the NOACs compared to their counterparts without leg ulcers. This finding lends credence to the hypothesis that sickle cell patients with leg ulcers have a procoagulant phenotype (Am J Hematol. 2011 Aug; 86: 705-8, Am J Hematol. 2014 Jan; 89: 1-6). Whether this translates to an increased risk of thromboembolic events remains uncertain. From our findings, it may not be the case for DVTs and PEs. However, further studies evaluating other clinical manifestations such as priapism, PH, stroke, avascular necrosis, and retinopathy, are still needed. Future directions include further correlation with the above-mentioned manifestations to provide a more comprehensive picture.
Minniti:Bluebird Bio: Other: Adjudicating Committee; Global Blood Therapeutics: Research Funding; Bayer: Research Funding; Teutona: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees.
Asterisk with author names denotes non-ASH members.