In Africa, a High Proportion of Adults with HbSC Meet American Society of Hematology's Eligibility Criteria for Severe Sickle Cell Disease and Starting Hydroxyurea Therapy in a Clinical Trial Setting

Introduction: Sickle cell disease (SCD), HbSC, is the second most frequent hemoglobinopathy after HbSS. Worldwide, an estimated 54,736 babies are delivered annually with HbSC disease, with the highest HbC gene frequency in West Africa (Piel et al.2013). A retrospective study at the Ghana Institute of Clinical Genetics [(GICG), a sickle cell clinic] reported that 40% of the 3,000 SCD patients attending the clinic yearly are HbSC (Asare et al.2018). HbSC disease usually results in a comparatively milder form of SCD. However, rates of maternal-fetal morbidity, retinopathy, avascular necrosis (AVN) of the hip, priapism, and chronic kidney disease are increased (Powars et al.2002; Oppong et al.2018). While microalbuminuria is lower in HbSC than HbSS, it still occurs in >23% of adults (Drawz et al.2016). In addition, thrombosis, silent cerebral infarction, sensorineural hearing loss, and pulmonary hypertension may be higher than previously suspected (Sathi et al.2019). Unlike HbSS, hydroxyurea is not routinely recommended for HbSC patients because they are all perceived to have a milder phenotype, with improved life expectancy. Thus, HbSC individuals are often excluded from randomized controlled trials in children and adults with SCD (Luchtman-Jones et al.2016).

Given the high proportion of adults with HbSC in Ghana, who may benefit from hydroxyurea therapy, we tested the hypothesis that at least 5% of adults with HbSC will meet the ASH criteria for severe disease and treatment. Data indicating that a significant proportion of adults with HbSC are eligible for hydroxyurea could potentially support pilot safety trials to determine the optimal hydroxyurea dose to ameliorate symptoms while limiting toxicity. Data can also facilitate government health policy decisions to subsidize hydroxyurea costs.

Methodology: We conducted a medical chart review of all adults with HbSC disease (total: 639; 18-45years) who attended the SCD clinic, GICG (January 1, 2019, to December 31, 2019). We identified a comparison group of 639 adults with HbSS, age, and gender-matched to the HbSC patients from the same clinic. Severe complications were defined as a history of ≥3 sickle cell-associated moderate to severe pain episodes/year, a history of severe acute chest syndrome (ACS), and severe symptomatic chronic anemia that interferes with daily activities or quality of life (Hydroxyurea and Transfusion Therapy for the Treatment of Sickle Cell Disease.2014). We defined acute pain episode as new onset of pain that lasts at least 4 hours, for which there is no explanation other than vaso-occlusion, which requires therapy with parenteral opioids in a medical setting (Ballas et al.2010). Severe symptomatic chronic anemia was defined as a drop in hemoglobin by ≥2g/dL below the steady state. Data were analyzed using SPSS version 23 and summarized as simple descriptive statistics. Study endpoints were the proportion of individuals with SCD who met the definition of severe disease and were eligible for hydroxyurea. We also calculated the pain and ACS incidence rates.

Results: The 639 HbSC participants had a mean age of 30.8years during the one-year study period, which was identical to that of the HbSS group. At least 8.5% of HbSC adults had ≥three acute pain episodes/ year, while 1.6% had ACS. No HbSC patient had severe symptomatic chronic anemia . In total, 10.0%(64/639) of patients with HbSC disease met the eligibility criteria for hydroxyurea therapy, compared to 24.1%(154/639) of patients with HbSS, p=<0.001. The pain and ACS incidence rates for the HbSC and HbSS individuals were [74.6; 95% CI(67.9-81.3) and 2.3; 95% CI(1.2-3.5)] events per 100 patient-years vs. [123.0; 95% CI(114.4-131.6) and 5.6; 95% CI(3.8-7.5)] events per 100 patient-years respectively. Also, 1.1%(7/639), 7.7%(49/639), 0.5%(4/639), and 4.4%(11/252) of patients with HbSC had papillary necrosis, AVN, stroke, and priapism, respectively while 8.5%(54/639) of patients with HbSS had proteinuria, Table 1. Only 0.9%(HbSC) and 2.3%(HbSS) took hydroxyurea during the study period.

Conclusion: Based on ASH's evidence-based guidelines, in a large SCD clinic at an academic medical center in Ghana, 10.0% of HbSC adults meet the criteria for shared decision-making to consider starting hydroxyurea therapy in a clinical trial setting. The optimal dose of hydroxyurea that maximizes benefit and minimizes toxicity in adults with HbSC is yet to be determined.

Figure 1

View largeDownload slide

Figure 1

View largeDownload slide

Close modal