High bias and low precision for estimated versus measured glomerular filtration rate in pediatric sickle cell anemia

Evaluation of eGFR methods in a sub-Saharan African community-based pediatric population

BACKGROUND

Accurate assessment of the estimated glomerular filtration rate (eGFR) plays a pivotal role in the early detection, management, and optimal medication dosing for chronic kidney disease (CKD). However, validation of eGFR, utilizing cystatin C-based equations, is limited in African children and adolescents with CKD. We evaluate the agreement of eGFR equations incorporating both cystatin C and creatinine in this specific population.

METHODS

This community-based study assessed CKD in children (2-15 years) using cystatin C and serum creatinine. eGFR agreement with the reference was evaluated with Bland-Altman plots, ROC curves, and Lin's CCC, using the Under-25 serum creatinine-cystatin C equation as the reference standard. Pairwise ROC comparisons assess the statistical differences in estimation equation agreement.

RESULTS

Among 666 children (mean age, 7.8 ± 3.8 years; 48.6% male), CKD prevalence was 11.6% (95% CI, 9.2-14.2%). Notably, the Chehade equation, using combined biomarkers, aligned best with the reference, displaying the lowest mean deviation (- 0.59; 95% CI, - 1.19 to 0.01), superior agreement (P10, 91.0%; P30, 96.70%), and highest discriminatory power (0.989). In contrast, CKD-EPI 2012 cystatin C had the highest mean deviation (- 35.90) and lowest discriminatory power (0.79). Equations combining creatinine and cystatin C (Schwartz, Chehade, Full Age Spectrum) demonstrated strong positive Lin's CCC with CKiD U25 creatinine-cystatin C, while Bouvet showed a notably weak correlation (Lin's CCC, 0.22).

CONCLUSION

In African children with CKD, the Chehade, CKiD Under 25 creatinine-based equations, and the Full Age Spectrum equations show promise for CKD diagnosis. However, a measured GFR is essential to identifying the most accurate eGFR equation in this population.

Enuresis and Hyperfiltration in Children With Sickle Cell Disease

Nocturnal enuresis is a common symptom in children with sickle cell disease (SCD). Risk factors for development of enuresis are currently unknown. An early manifestation of SCD-associated kidney damage is glomerular hyperfiltration. We test the hypothesis that in a pediatric SCD cohort, individuals with hyperfiltration are more likely to have nocturnal enuresis when compared to children without hyperfiltration. To assess the relationship between nocturnal enuresis and hyperfiltration, we retrospectively evaluated children with SCD enrolled in the Evaluation of Nocturnal Enuresis and Barriers to Treatment among Pediatric Patients with SCD study and prospectively identified children who reported nocturnal enuresis and were enrolled in the longitudinal cohort study Sickle Cell Clinical Research and Intervention Program. Nocturnal enuresis occurred in 46.5% of Pediatric Patients with Sickle Cell Disease participants and was more frequent in participants with HbSS/HbSβ 0 thalassemia and in male participants. We did not identify an association between hyperfiltration from 3 to 5 years of age with the later development of enuresis. Severe SCD genotypes and male sex were associated with nocturnal enuresis after age 5 years. We could not identify additional renal or hematologic predictors associated with the diagnosis of nocturnal enuresis. Future studies should incorporate nonrenal risk factors into studies that predict development of enuresis.

Longitudinal Study of Glomerular Hyperfiltration in Adults with Sickle Cell Anemia: A Multicenter Pooled Analysis

Glomerular hyperfiltration is common in young sickle cell anemia patients and precedes development of overt kidney disease. In this multicenter pooled cohort, we characterized hyperfiltration and its decline to normal range in adult patients. Glomerular filtration rate (GFR) was estimated using the creatinine-based 2009 CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation omitting race adjustment and the 2021 CKD-EPI equation. Using CKD-EPI–2009, 506 patients had baseline estimated GFR (eGFR) ≥90 mL/min per 1.73 m², median age of 24 (interquartile range [IQR], 19-34) years and 5.17 years of follow-up. The prevalence of hyperfiltration (eGFR ≥140 and ≥130 mL/min per 1.73 m² for men and women, respectively) was 38.3%. Using CKD-EPI–2009, baseline hyperfiltration was less likely with older age (odds ratio [OR], 0.78; 95% confidence interval [CI], 0.73-0.83; P < .0001), male sex (OR, 0.32; 95% CI, 0.18-0.58; P = .0002), and higher weight (OR, 0.96; 95% CI, 0.94-0.99; P = .001). Using CKD-EPI–2021, hyperfiltration was similarly less likely with older age (OR, 0.75; 95% CI, 0.70-0.81; P < .0001), male sex (OR, 0.24; 95% CI, 0.13-0.44; P < .0001), and higher weight (OR, 0.97; 95% CI, 0.95-0.99; P = .004). In patients with baseline hyperfiltration, eGFR declined to normal values at a median age of 26.2 years. Using CKD-EPI–2009, this decline was associated with male sex (HR, 2.20; 95% CI, 1.26-3.87; P = .006), systolic blood pressure (hazard ratio [HR], 1.02; 95% CI, 1.01-1.04; P = .01), and hydroxyurea use (HR, 1.74; 95% CI, 1.002-3.03; P = .05). Using CKD-EPI–2021, decline of eGFR to normal was only associated with male sex (HR, 3.39; 95% CI, 2.01-5.69; P < .0001). Decline to normal eGFR range from hyperfiltration occurs earlier in males, those on hydroxyurea, and with higher systolic blood pressure.

The nephropathy of sickle cell trait and sickle cell disease

Sickle cell syndromes, including sickle cell disease (SCD) and sickle cell trait, are associated with multiple kidney abnormalities. Young patients with SCD have elevated effective renal plasma flow and glomerular filtration rates, which decrease to normal ranges in young adulthood and subnormal levels with advancing age. The pathophysiology of SCD-related nephropathy is multifactorial - oxidative stress, hyperfiltration and glomerular hypertension are all contributing factors. Albuminuria, which is an early clinical manifestation of glomerular damage, is common in individuals with SCD. Kidney function declines more rapidly in individuals with SCD than in those with sickle cell trait or in healthy individuals. Multiple genetic modifiers, including APOL1, HMOX1, HBA1 and HBA2 variants are also implicated in the development and progression of SCD-related nephropathy. Chronic kidney disease and rapid decline in estimated glomerular filtration rate are associated with increased mortality in adults with SCD. Renin-angiotensin-aldosterone system inhibitors are the standard of care treatment for albuminuria in SCD, despite a lack of controlled studies demonstrating their long-term efficacy. Multiple studies of novel therapeutic agents are ongoing, and patients with SCD and kidney failure should be evaluated for kidney transplantation. Given the high prevalence and severe consequences of kidney disease, additional studies are needed to elucidate the pathophysiology, natural history and treatment of SCD-related nephropathy.

Reliability of different estimated glomerular filtration rate as measures of renal function in children with sickle cell disease

BACKGROUND

There is no reliable marker for detecting early renal disease in early children with sickle cell disease (SCD). Estimation of glomerular filtration rate (eGFR) as derived from the height/plasma creatinine formula is dependent on the accuracy of the creatinine analytical method used. The aim of this study was to evaluate different equations for eGFR.

METHODS

Children aged 5-16 years recruited. mGFR was obtained using plasma disappearance of Inutest/Iohexol, serum creatinine (SCr) was measured either by standard laboratory method or by tandem mass spectrometry (MSMS). Estimated GFR was then calculated either by "Bedside Schwartz method" or by the full-age spectrum (FAS) equation.

FINDINGS

A total of 79 patients (mean age 9.8 ± 4.0 years). A revised eGFR constant was calculated for Schwartz equation from the slope of the plot of height/plasma creatinine versus mGFR. Mean values for mGFR (132.7 ± 32.1 ml/min/1.73m²) and eGFR methods compared: eGFR from standard SCr was significantly higher (144.2 ± 37.3 ml/min/1.73m², p = 0.008). The MSMS eGFR showed the lowest SD (SD = 27.5), while both FAS eGFR and FAS-height eGFR showed the highest correlation coefficient (r = 0.67).

INTERPRETATION

eGFR calculation based on height and SCr determined with MSMS traceable creatinine is more reliable than Schwartz formula using jaffe/enzymatic methods in SCD children.