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Introduction Among the risk factors for venous thromboembolism (VTE) are inheritance of the sickle cell gene and antiphospholipid syndrome. Antiphospholipid antibodies are elevated in sickle cell disease but there is little information on its levels in sickle cell trait. The prevalence of anticardiolipin antibodies and association with VTE is equally not known in the Nigerian population. Methods A case control study involving 50 consecutive patients with Doppler confirmed venous thromboembolism at the University College Hospital Ibadan and 50 apparently healthy individuals. Haemoglobin electrophoresis was carried out using cellulose acetate membrane. IgG and IgM anticardiolipin antibodies were assayed by ELISA. Results The mean age of the patients was 58.7±18.5years, range of 21-89 years, there were 21 males (42%). Majority of the patients (42 (84%)) had deep venous thrombosis while five (10%) patients presented with pulmonary embolism, one had both deep venous thrombosis and pulmonary embolism. A patient had portal vein thrombosis and another, an intracardiac clot. Sedentary lifestyles, hypertension and concomitant malignancy were the most prevalent risk factors (34% each) (figure I). Both sedentary lifestyle and cancer were significantly associated with VTE (p Conclusion The prevalence of sickle cell trait and anticardiolipin levels did not differ between VTE patients and healthy controls. Age, hypertension, sedentary lifestyle and malignancies were identified risk factors in our cohort of patients. Larger prospective studies may be helpful in determining the influence of sickle cell trait and antiphospholipid antibodies in venous thromboembolism. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

More recent evidence however suggests the likelihood of four independent mutations of the sickle cell gene in different populations; three of which occurred in Africa. The trans-Atlantic slave trade accounted for the gene movement from Africa to the Caribbean and United States of America and lately migration has resulted in the introduction of the gene to the United Kingdom and other parts of Europe. The incidence of SCD in England (1:200 births) is increasing and the high prevalence is due to the high percentage of births to mothers of West African origin.

Alpha-thalassemia and the BCL11A rs1427407 T allele are commonly observed in sickle cell anemia (SCA) patients and are associated with reduced hemolysis and higher hemoglobin F levels, respectively. We investigated whether a high-risk genetic profile, defined as SCA patients who did not inherit either α-thalassemia or the BCL11A rs1427407 T allele, had stronger associations with clinical and laboratory variables than the individual genetic components in the University of Ibadan cohort (n=249). We then replicated our findings in SCA cohorts from the University of Illinois at Chicago (UIC)(n=260) and Walk-Treatment of Pulmonary Hypertension and Sickle cell disease with Sildenafil Therapy (Walk-PHaSST)(n=387). High-risk was associated with higher reticulocytes (15.0% vs. 7.8%, P=0.08) and stroke history (6% vs. 1%, P=0.02) than standard risk patients and these associations were more significant than the individual genetic components in the University of Ibadan cohort. These findings were replicated in high-risk patients from UIC and Walk-PHaSST for reticulocytes (UIC: 13.5% vs. 11.8%, P=0.03; Walk-PHaSST: 9.6% vs. 8.2%, P=0.0003) and stroke history (UIC: 32% vs. 22%, P=0.07; Walk-PHaSST: 14% vs. 7%, P=0.01). On combined analysis, high-risk had strong associations with increased markers of hemolysis (hemoglobin β= -0.29, 95%CI: -0.50 to -0.09; P=0.006; reticulocyte% β=2.29, 95%CI: 1.31 to 3.25; P=1x10-5) and stroke history (OR=2.0, 95%CI: 1.3 to 3.0; P=0.0002), but no association with frequent vaso-occlusive crises (≥3/year). A high-risk genetic profile is associated with increased hemolysis and stroke history in three independent cohorts. This profile may help identify patients to prioritize for hydroxyurea and for closer monitoring strategies for stroke.

Background. Despite a large body of evidence that hydroxyurea is effective for sickle cell anemia (SCA), utilization with the "maximum tolerated dose" regimen has been low.1 Hydroxyurea therapy for SCA increases hemoglobin F, reduces pain crises, acute chest syndrome and blood transfusions, and possibly increases survival.2 The increase in hemoglobin F with hydroxyurea is related to the plasma level achieved, which depends on the dose.3 Hydroxyurea is typically initiated at 15 mg/kg/day followed by dose escalations up to 35 mg/kg/day if tolerated - the "maximum tolerated dose" approach used in the seminal Multicenter Study of Hydroxyurea (MSH) in the 1990's.4 With this approach, neutropenia and thrombocytopenia are limitations to achieving maximal dose and frequent blood count monitoring is required.These considerations limit the use of hydroxyurea in areas of the world where frequent blood monitoring is not feasible, and they also cause primary care providers in the US to hesitate to prescribe the medication. Methods. We recently reported a trial of hydroxyurea (500 mg/day orally) in 48 adults with SCA in Ibadan, Nigeria - a "fixed low-dose" approach.5 In the present report, we compare hematologic responses in 38 per protocol patients from the Ibadan study (received at least five of the planned six 4-weekly supplies of hydroxyurea)5 to the responses in 152 patients in the MSH study.6 Results. Baseline hematologic values for the two studies are shown in Table 1. Over the first 12 to 14 weeks of hydroxyurea, responses in hemoglobin, mean corpuscular volume (MCV), and platelets were similar in the two studies (Figure 1). At end-of-study (24 weeks Ibadan and 104 weeks MSH) responses in hemoglobin F and complete blood count were similar, except that the decline in neutrophil count in the Ibadan cohort was significantly less than the decline in MSH after the Bonferroni correction for multiple comparisons (Table 1and Figure 2). At this time the median (range) dose of hydroxyurea per body weight was 10 (7-14) mg/kg per day in the 38 Ibadan patients versus 20 (2.5-35) mg/kg per day in the 119 patients who remained on hydroxyurea in the MSH study.6 We performed a review of the medical records in the Ibadan patients. There were seven acute non-infectious complications in the 38 patients while taking fixed low-dose hydroxyurea for 24 weeks (admission for pain or acute chest syndrome) versus 17 while being observed off hydroxyurea for 24 weeks (pain, acute chest syndrome, need for blood transfusion, heart failure or death) (Table 2). Incidence of infections was similar during 24 weeks of fixed low-dose hydroxyurea and during 24 weeks of observation off hydroxyurea (Table 2). Discussion. These findings suggest that a "fixed low-dose" regimen may have substantial clinical benefit. Such a regimen would have a low chance of inducing cytopenias, would be straightforward for primary care providers to prescribe and would be ideal to test in combination therapy regimens for SCA. It would also be cost-efficient and affordable, especially for patients in low and middle-income countries where access to health insurance is lacking. We propose that the clinical efficacy of "fixed low-dose" hydroxyurea for SCA should be investigated further. We believe that a randomized comparison of the efficacy and safety of the "fixed low-dose" and "maximum tolerated dose" regimens should be a high priority. References Stettler N, McKiernan CM, Melin CQ, Adejoro OO, Walczak NB. Proportion of adults with sickle cell anemia and pain crises receiving hydroxyurea. JAMA 2015;313:1671-2. Platt OS. Hydroxyurea for the treatment of sickle cell anemia. N Engl J Med 2008;358:1362-9. Charache S, Dover GJ, Moore RD, et al. Hydroxyurea: effects on hemoglobin F production in patients with sickle cell anemia. Blood 1992;79:2555-65. Charache S, Terrin ML, Moore RD, et al. Effect of hydroxyurea on the frequency of painful crises in sickle cell anemia. Investigators of the Multicenter Study of Hydroxyurea in Sickle Cell Anemia. N Engl J Med 1995;332:1317-22. Tayo BO, Akingbola TS, Saraf SL, et al. Fixed Low-Dose Hydroxyurea for the Treatment of Adults with Sickle Cell Anemia in Nigeria. Am J Hematol 2018. Charache S, Barton FB, Moore RD, et al. Hydroxyurea and sickle cell anemia. Clinical utility of a myelosuppressive "switching" agent. The Multicenter Study of Hydroxyurea in Sickle Cell Anemia. Medicine (Baltimore) 1996;75:300-26. Disclosures Hsu: Global Blood Therapeutics: Research Funding; Astra Zeneca: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Ironwood: Research Funding; Emmi: Consultancy; Hilton Publishing: Consultancy; Gerson Lehman Group: Consultancy; Guidepoint: Consultancy.

Background: The vast majority of births with sickle cell anemia occur in Africa 1 and early-life mortality, generally before age five years, is as high as 90% 2,3. Hydroxyurea was approved for sickle cell anemia by the US FDA in 1998 but is not commonly used in Africa due to fear of toxicity, lack of awareness and limited availability. Hemoglobin F is a protective factor that decreases severity of sickle cell anemia, and hydroxyurea treatment leads to an increase in hemoglobin F. In the US, hydroxyurea is typically initiated at a dose of 15 mg/kg followed by dose escalations of up to 35 mg/kg if tolerated with a goal of maximal tolerated dose and maximal response in hemoglobin F. Neutropenia and thrombocytopenia are the usual limitations to achieving maximal dose. In the landmark Multicenter Study of Hydroxyurea, the clinical response to hydroxyurea correlated strongly with a reduction in the neutrophil count as well as an increase in the fetal hemoglobin concentration as reflected in percentage of F cells. A striking decrease in pain crises was observed in the first three months of therapy, before dose escalation and before maximal increase in hemoglobin F levels 4. Furthermore, hydroxyurea in the range of 10-15.9 mg/kg/day was reportedly effective in decreasing the frequency of pain episodes in children and adolescents in Oman 5, and hydroxyurea 10 mg/kg/day decreased pain episodes in children and adults with sickle cell anemia in India 6. From these perspectives, we reasoned that a fixed dose of hydroxyurea 10 mg/kg/day is reasonable to investigate in the African setting where the safety in relationship to the resources and infectious exposures is not known. Methods: We assigned 48 sickle cell anemia patients to hydroxyurea 500 mg/day for 24 weeks to determine safety and efficacy; 28 had high-risk disease based on hemoglobin F Results: The median (interquartile range) age was 25 (22-27) years and the median hydroxyurea dose 9.8 (9.1-10.4) mg/kg per day. The patients complied with treatment for a median of 20 (16-24) weeks. Four (8.3%) developed a pre-specified adverse outcome: clinical malaria (N=2), thrombocytopenia in combination with malaria (N=1), pulmonary tuberculosis (N=1). During therapy the median hemoglobin increased by 9.0 g/L, mean corpuscular volume by 11.2 fL and body weight by 3.0 kg while median white blood cells declined by 2600 per uL and platelets by 127,000 per uL (P Conclusion: Our results suggest that low, fixed-dose dose hydroxyurea for sickle cell anemia in Nigeria is associated with a low adverse outcome rate and with improvements in blood counts, hemoglobin F and body weight. The effects on vaso-occlusive episodes and on the risks of recrudescent tuberculosis and malaria-associated thrombocytopenia should be assessed in further studies. Acknowledgment: Supported by a grant from the Doris Duke Foundation. References 1. Williams TN, Obaro SK. Sickle cell disease and malaria morbidity: a tale with two tails. Trends Parasitol 2011;27:315-20. 2. Grosse SD, Odame I, Atrash HK, Amendah DD, Piel FB, Williams TN. Sickle cell disease in Africa: a neglected cause of early childhood mortality. Am J Prev Med 2011;41:S398-405. 3. Makani J, Cox SE, Soka D, et al. Mortality in sickle cell anemia in Africa: a prospective cohort study in Tanzania. PLoS One 2011;6:e14699. 4. Charache S, Barton FB, Moore RD, et al. Hydroxyurea and sickle cell anemia. Clinical utility of a myelosuppressive "switching" agent. The Multicenter Study of Hydroxyurea in Sickle Cell Anemia. Medicine (Baltimore) 1996;75:300-26. 5. Sharef SW, Al-Hajri M, Beshlawi I, et al. Optimizing Hydroxyurea use in children with sickle cell disease: low dose regimen is effective. Eur J Haematol 2013. 6. Patel DK, Mashon RS, Patel S, Das BS, Purohit P, Bishwal SC. Low dose hydroxyurea is effective in reducing the incidence of painful crisis and frequency of blood transfusion in sickle cell anemia patients from eastern India. Hemoglobin 2012;36:409-20. Disclosures Ezekekwu: American Society of Hematology: Other: The Visitor training program was sponsored by ASH. Hsu: AstraZeneca steering committee for HESTIA trial: Research Funding. Gordeuk: Emmaus Life Sciences: Consultancy.

Introduction: Chronic hemolysis occurs in sickle cell anemia as a result of recurrent sickling and other abnormalities of the red blood cells including eryptosis. Exuberant reticulocytosis is anticipated to partially compensate for the resultant anemia. Sickle cell anemia patients may also have aplastic crisis, bone marrow (BM) infarction and erythropoietin deficiency which could lead to reticulocytopenia despite the anemia. High degree of reticulocytosis among asymptomatic infants with sickle cell anemia has been associated with an increased risk of death or stroke during childhood. Assessment of BM function in sickle cell anemia is important due to potential complications associated with both under-activity and hyperactivity. This study aimed at evaluating the erythropoietic function of the BM in steady state sickle cell anemia using corrected reticulocyte counts. Methods: This study was carried out at the hematology clinic in the University College Hospital, Ibadan. HbSS patients in steady state were recruited from the hematology clinic. Local ethical committee approval was obtained and all participants gave written informed consent. Patients with M. tuberculosis, Hepatitis B, HIV and P. falciparum infection were excluded. Peripheral blood samples were analyzed using Sysmex Ki-X21 for complete blood count (CBC) and standard point of care for serum electrolytes and liver function tests. The glomerular filtration rates were calculated using the Cockcroft-Gault formula. Reticulocyte counts were determined manually using fresh samples from K2 EDTA bottles and methylene blue stain. Two drops of stain were mixed with two to four volumes of anticoagulated blood and incubated at 37ºC for 15 minutes. Afterwards, the cells were re-suspended and blood films were made. Corrected reticulocyte count and reticulocyte production index were calculated. Participants were categorized according to corrected reticulocyte counts of greater than or less than 2.5%. Univariate and multivariate analyses were performed to determine variables associated with corrected reticulocyte count Results: 92 HbSS patients were recruited with a mean (SD) age of 19.6 (5.8) years. There was no correlation between age and eGFR (p-value: 0.227). Median (range) reticulocyte count, corrected reticulocyte count and reticulocyte production index were 5.5 (0.5 - 29.9), 3.3 (0.1 - 17.1) and 1.7 (0.2 - 8.6) respectively. 40 (43.5%) patients had corrected reticulocyte count 2.5%. Those corrected reticulocyte count 2.5% (Table 1). CBC parameters were not different when compared between both groups. Results of multivariate logistic regression analysis carried out showed that only AST was independently linked with corrected reticulocyte count Table 1. Factors Associated with Low Reticulocyte Count Corrected count2.5% p-Value Age (Mean, SD) 21.4 (6.3) 18.4 (5.0) 0.013 Gender (N, %) Male 22 (55.0) 28 (53.8) 0.912 Female 18 (45.0) 24 (46.2) Height (Mean, SD) 1.6 (0.1) 1.5 (0.1) 0.041 BMI (Mean, SD) 18.7 (3.1) 18.7 (3.0) 0.753 GFR (Mean, SD) 64.3 (37.7) 66.4 (29.3) 0.453 Bilirubin (Mean, SD) 1.7 (1.1) 1.9 (2.6) 0.674 AST (Mean, SD) 22.5 (13.5) 14.5 (6.6) 0.006 ALT (Mean, SD) 13.4 (7.7) 14.4 (11.1) 0.876 Table 2. Independent Predictors of Corrected Reticulocyte Count Conclusion: Despite corrected reticulocyte count Disclosures No relevant conflicts of interest to declare.