Patients with sickle cell disease who develop end-stage kidney disease continue to experience poor survival - A 19-year United States Renal Data System study

Development of Polygenic Risk Score for Persistent Albuminuria in Children and Adults With Sickle Cell Anemia

Albuminuria is associated with high-risk apolipoprotein-L1 variants (APOL1 G1/G2) in patients with sickle cell anemia (SCA). However, this gene variant does not account for all chronic kidney disease (CKD) risk. We hypothesized that we could develop a polygenic risk score (PRS) for CKD in SCA, combining APOL1 G1/G2 with other candidate genes that modify SCA severity and further stratify patients into risk categories based on this risk score. Variants in APOL1, HMOX1 (rs743811), BCL11A (rs1424407), and α-thalassemia (α-3.7) were identified in children with SCA enrolled in the Sickle Cell Clinical Research and Intervention Program longitudinal cohort (SCCRIP). We individually tested the association of these variants with persistent albuminuria, tested a three-variant PRS (PRS-3) (APOL1, BCL11A (rs1424407), and α-3.7), and developed a four-variant PRS (PRS-4) after adding HMOX1 (rs743811) to PRS-3 using the summation of high-risk alleles. An adult SCA cohort from the University of Illinois, Chicago (UIC), was used for validation. Persistent albuminuria was defined as having a urine albumin-to-creatinine ratio (UACR) ≥ 30 mg/g on at least 2 of 3 consecutive measurements. In both cohorts, APOL1 risk variants increased the risk while α-thalassemia protected against persistent albuminuria. PRS-4 was significantly associated with persistent albuminuria (SCCRIP: p = 0.004; UIC: p = 0.00016). When stratifying patients into three and four risk categories based on the PRS, 58% and 86% of the high-risk (PRS-3) and 54% and 89% of very high-risk (PRS-4) categories developed persistent albuminuria cases in the SCCRIP and UIC cohorts, respectively. A PRS may identify high-risk SCA patients for albuminuria. Applying this PRS to guide the early implementation of disease modifiers and renoprotective therapies may help reduce the burden of SCA-related CKD. Trial Registration: NCT02098863.

Prevalence, Mortality, and Access to Care for Chronic Kidney Disease in Medicaid-Enrolled Adults With Sickle Cell Disease in California: Retrospective Cohort Study

BACKGROUND

Chronic kidney disease (CKD) is a significant complication in patients with sickle cell disease (SCD), leading to increased mortality.

OBJECTIVE

This study aims to investigate the burden of CKD in Medicaid-enrolled adults with SCD in California, examine differences in disease burden between male and female individuals, and assess mortality rates and access to specialized care.

METHODS

This retrospective cohort study used the California Sickle Cell Data Collection program to identify and monitor individuals with SCD. Medicaid claims, vital records, emergency department, and hospitalization data from 2011 to 2020 were analyzed. CKD prevalence was assessed based on ICD (International Classification of Diseases) codes, and mortality rates were calculated. Access to specialized care was examined through outpatient encounter rates with hematologists and nephrologists.

RESULTS

Among the 2345 adults with SCD, 24.4% (n=572) met the case definition for CKD. The SCD-CKD group was older at the beginning of this study (average age 44, SD 14 vs 34, SD 12.6 years) than the group without CKD. CKD prevalence increased with age, revealing significant disparities by sex. While the youngest (18-29 years) and oldest (>65 years) groups showed similar CKD prevalences between sexes (female: 12/111, 10.8% and male: 12/101, 11.9%; female: 74/147, 50.3% and male: 34/66, 51.5%, respectively), male individuals in the aged 30-59 years bracket exhibited significantly higher rates than female individuals (30-39 years: 49/294, 16.7%, P=.01; 40-49 years: 52/182, 28.6%, P=.02; and 50-59 years: 76/157,48.4%, P<.001). During this study, of the 2345 adults, 435 (18.5%) deaths occurred, predominantly within the SCD-CKD cohort (226/435, 39.5%). The median age at death was 53 (IQR 61-44) years for the SCD-CKD group compared to 43 (IQR 33-56) years for the SCD group, with male individuals in the SCD-CKD group showing significantly higher mortality rates (111/242, 45.9%; P=.009) than female individuals (115/330, 34.9%). Access to specialist care was notably limited: approximately half (281/572, 49.1%) of the SCD-CKD cohort had no hematologist visits, and 61.9% (354/572) did not see a nephrologist during this study's period.

CONCLUSIONS

This study provides robust estimates of CKD prevalence and mortality among Medicaid-enrolled adults with SCD in California. The findings highlight the need for improved access to specialized care for this population and increased awareness of the high mortality risk and progression associated with CKD.

Beyond pulmonary embolism: Alternative diagnosis and incidental findings on CT pulmonary angiography in sickle cell disease

BACKGROUND

Sickle cell disease (SCD) is a genetic hematological disorder associated with severe complications, such as vaso-occlusive crises, acute chest syndrome (ACS), and an increased risk of thromboembolic events, including pulmonary embolism (PE). The diagnosis of PE in SCD patients presents challenges due to the overlapping symptoms with other pulmonary conditions. Our previous study revealed that nearly 96% of computed tomography pulmonary angiography (CTPA) scans in SCD patients were negative for PE, highlighting a gap in understanding the significance of CTPA findings when PE is absent.

METHODS

In this retrospective follow-up study conducted at the Salmaniya Medical Complex in Bahrain, we examined SCD patients with HbSS genotypes who underwent CTPA from January 1, 2018, to December 31, 2021, for suspected PE, but the results were negative. The aim of this study was to identify alternative diagnoses and incidental findings from CTPA scans. Experienced radiologists reviewed the CTPA images and reports to assess potential alternative diagnoses and incidental findings, incorporating an additional analysis of chest X-rays to evaluate the diagnostic value of CTPA. Incidental findings were classified based on their location and clinical significance.

RESULTS

Among the 230 evaluated SCD patients (average age 39.7 years; 53% male) who were CTPA negative for PE, 142 (61.7%) had identifiable alternative diagnoses, primarily pneumonia (49.1%). Notably, 88.0% of these alternative diagnoses had been previously suggested by chest radiographs. Furthermore, incidental findings were noted in 164 (71.3%) patients, with 11.0% deemed clinically significant, necessitating immediate action, and 87.8% considered potentially significant, requiring further assessment. Notable incidental findings included thoracic abnormalities such as cardiomegaly (12.2%) and an enlarged pulmonary artery (11.3%), as well as upper abdominal pathologies such as hepatomegaly (19.6%), splenomegaly (20.9%), and gallstones (10.4%).

CONCLUSION

This study underscores the limited additional diagnostic yield of CTPA for identifying alternative diagnoses to PE in SCD patients, with the majority of diagnoses, such as pneumonia, already suggested by chest radiographs. The frequent incidental findings, most of which necessitate further evaluation, highlight the need for a cautious and tailored approach to using CTPA in the SCD population.

Blood pressure thresholds for the diagnosis of hypertensive disorders of pregnancy in sickle cell disease

In this retrospective cohort study of singleton pregnancies in people with sickle cell disease (SCD) delivered at two academic centres between 1990 and 2021, we collected demographic and SCD-related data, pregnancy outcomes, and the highest systolic and diastolic blood pressure (SBP and DBP) at seven time periods. We compared the characteristics of subjects with new or worsening proteinuria (NWP) during pregnancy to those without. We then constructed receiver operating characteristic (ROC) curves to determine the blood pressure (BP) that best identifies those with NWP. The SBP or DBP thresholds which maximized sensitivity and specificity were 120 mmHg SBP (sensitivity: 55.2%, specificity: 73.5%) and 70 mmHg DBP (sensitivity: 27.6%, specificity: 67.7%). The existing BP threshold of 140/90 mmHg lacked sensitivity in both genotype groups (HbSS/HbSβ0 : SBP = 21% sensitive, DBP = 5.3% sensitive; HbSS/HbSβ+ : SBP = 10% sensitive, DBP = 0% sensitive). Finally, percent change in SBP, DBP and MAP were all poor tests for identifying NWP. Existing BP thresholds used to diagnose hypertensive disorders of pregnancy (HDP) are not sensitive for pregnant people with SCD. For this population, lowering the BP threshold that defines HDP may improve identification of those who need increased observation, consideration of early delivery and eclampsia prophylaxis.

Natural history and variability in albuminuria in pediatric and murine sickle cell anemia

It is critical to characterize the natural history of albuminuria in patients with sickle cell anemia (SCA); however, these data are currently lacking and affecting evidence-based guidelines. We performed a natural history study of the development of pediatric albuminuria. We identified participants with hemoglobin SS/SB0 thalassemia ≥5 years with albumin to creatinine ratio (ACR) measurements performed at a steady-state clinic visit. Participants were characterized as either persistent, intermittent, or never albuminuria. We determined the prevalence of persistent albuminuria, use of ACR ≥100 mg/g as a predictor, and variation in ACR measurements. We mirrored this study to determine the variation in albuminuria measurements in the SCA murine model. Among 355 participants with HbSS/SB0 thalassemia with 1728 ACR measurements, we identified 17% with persistent and 13% with intermittent albuminuria. Thirteen percent of participants with persistent albuminuria developed an abnormal ACR before 10 years of age. A single ACR measurement ≥100 mg/g was associated with 55.5 times (95% confidence interval, 12.3-527) higher odds of having persistent albuminuria. Among participants with ACR ≥100 mg/g, we identified significant variability in the results of repeated measurements. The median ACR at the initial and next measurements were 175.8 mg/g (interquartile range [IQR], 135-242) and 117.3 mg/g (IQR, 64-292). The human variability in ACR was mirrored by ∼20% variability in albuminuria in murine model. This evidence suggests adopting standards for repeating ACR measurements, consider screening for ACR before 10 years of age, and using an ACR >100 mg/g as a risk factor for progression. Pediatric and murine renoprotective clinical trials need to consider the high variability in repeated ACR measurements.

Machine Learning Predicts Acute Kidney Injury in Hospitalized Patients with Sickle Cell Disease

INTRODUCTION

Acute kidney injury (AKI) is common among hospitalized patients with sickle cell disease (SCD) and contributes to increased morbidity and mortality. Early identification and management of AKI is essential to preventing poor outcomes. We aimed to predict AKI earlier in patients with SCD using a machine-learning model that utilized continuous minute-by-minute physiological data.

METHODS

A total of6,278 adult SCD patient encounters were admitted to inpatient units across five regional hospitals in Memphis, TN, over 3 years, from July 2017 to December 2020. From these, 1,178 patients were selected after filtering for data availability. AKI was identified in 82 (7%) patient encounters, using the 2012 Kidney Disease Improving Global Outcomes (KDIGO) criteria. The remaining 1,096 encounters served as controls. Features derived from five physiological data streams, heart rate, respiratory rate, and blood pressure (systolic, diastolic, and mean), captured every minute from bedside monitors were used. An XGBoost classifier was used for classification.

RESULTS

Our model accurately predicted AKI up to 12 h before onset with an area under the receiver operator curve (AUROC) of 0.91 (95% CI [0.89-0.93]) and up to 48 h before AKI with an AUROC of 0.82 (95% CI [0.80-0.83]). Patients with AKI were more likely to be female (64.6%) and have history of hypertension, pulmonary hypertension, chronic kidney disease, and pneumonia than the control group.

CONCLUSION

XGBoost accurately predicted AKI as early as 12 h before onset in hospitalized SCD patients and may enable the development of innovative prevention strategies.

Sickle Cell Disease and CKD: An Update

BACKGROUND

Sickle cell disease is an inherited red blood cell disorder that affects approximately 100,000 people in the USA and 25 million people worldwide. Vaso-occlusion and chronic hemolysis lead to dysfunction of vital organ systems, with the kidneys being among the most commonly affected organs.

SUMMARY

Early renal manifestations include medullary ischemia with the loss of urine-concentrating ability and hyperfiltration. This can be followed by progressive damage characterized by persistent albuminuria and a decline in the estimated glomerular filtration rate. The risk of sickle nephropathy is greater in those with the APOL1 G1 and G2 kidney risk variants and variants in HMOX1 and lower in those that coinherit α-thalassemia. Therapies to treat sickle cell disease-related kidney damage focus on sickle cell disease-modifying therapies (e.g., hydroxyurea) or those adopted from the nonsickle cell disease kidney literature (e.g., renin-angiotensin-aldosterone system inhibitors), although data on their clinical efficacy are limited to small studies with short follow-up periods. Kidney transplantation for end-stage kidney disease improves survival compared to hemodialysis but is underutilized in this patient population.

KEY MESSAGES

Kidney disease is a major contributor to early mortality, and more research is needed to understand the pathophysiology and develop targeted therapies to improve kidney health in sickle cell disease.