Abstract: We included two trials with 215 participants. One trial was published in 2011 and included 193 children aged 9 months to 18 months, and compared treatment with hydroxyurea to placebo. The second trial was published in 1998 and included 22 adults with normal blood pressure and microalbuminuria and compared ACEI to placebo. We rated the quality of evidence as low to very low across different outcomes according to GRADE methodology. This was due to trials having: a high or unclear risk of bias including attrition and detection bias; indirectness (the available evidence was for children aged 9 months to 18 months in one trial and a small and select adult sample size in a second trial); and imprecise outcome effect estimates of significant benefit or harm. Hydroxyurea versus placebo We are very uncertain if hydroxyurea reduces or prevents progression of kidney disease (assessed by change in glomerular filtration rate), or reduces hyperfiltration in children aged 9 to 18 months, mean difference (MD) 0.58 (95% confidence interval (CI) -14.60 to 15.76 (mL/min per 1.73 m²)) (one study; 142 participants; very low-quality evidence). In children aged 9 to 18 months, hydroxyurea may improve the ability to concentrate urine, MD 42.23 (95% CI 12.14 to 72.32 (mOsm/kg)) (one study; 178 participants; low-quality evidence). Hydroxyurea may make little or no difference to SCD-related serious adverse events including: incidence of acute chest syndrome, risk ratio (RR) 0.39 (99% CI 0.13 to 1.16); painful crisis, RR 0.68 (99% CI 0.45 to 1.02); and hospitalisations, RR 0.83 (99% CI 0.68 to 1.01) (one study, 193 participants; low-quality evidence). No deaths occurred in the trial. Quality of life was not reported. ACEI versus placebo We are very uncertain if ACEI reduces proteinuria in adults with SCD who have normal blood pressure and microalbuminuria, MD -49.00 (95% CI -124.10 to 26.10 (mg per day)) (one study; 22 participants; very low-quality evidence). We are very uncertain if ACEI reduce or prevent kidney disease as measured by creatinine clearance. The authors state that creatinine clearance remained constant over six months in both groups, but no comparative data were provided (very low-quality evidence). All-cause mortality, serious adverse events and quality of life were not reported. In young children aged 9 months to 18 months, we are very uncertain if hydroxyurea improves glomerular filtration rate or reduces hyperfiltration, but it may improve young children's ability to concentrate urine and may make little or no difference on the incidence of acute chest syndrome, painful crises and hospitalisations. We are very uncertain if giving ACEI to adults with normal blood pressure and microalbuminuria has any effect on preventing or reducing kidney complications. This review identified no trials that looked at red cell transfusions nor any combinations of interventions to prevent or reduce kidney complications. Due to lack of evidence this review cannot comment on the management of either children aged over 18 months or adults with any known genotype of SCD. We have identified a lack of adequately-designed and powered studies, and no ongoing trials which address this critical question. Trials of hydroxyurea, ACEI or red blood cell transfusion in older children and adults are urgently needed to determine any effect on prevention or reduction kidney complications in people with SCD.

Plain-language summary: We found two randomised controlled trials which enrolled a total of 215 participants. One trial, published in 2011, was conducted in 193 infants aged 9 months to 18 months and compared the drug hydroxyurea to placebo. The second trial, published in 1998, was conducted in 22 adults with normal blood pressure and microalbuminuria (an increase of protein in the urine) and compared captopril (a drug used to treat high blood pressure) to placebo. Both trials received government funding. In infants aged 9 months to 18 months, hydroxyurea may increase the ability to produce normal urine, but we are very uncertain if it has any effect on the glomerular filtration rate (network of filters in the kidney that filter waste from the blood). Hydroxyurea may make little or no difference on the incidence of SCD-related serious complications (including acute chest syndrome, painful crises and hospitalisations). We are very uncertain if giving captopril to adults with SCD who have normal blood pressure and early signs of kidney damage (microalbuminuria) reduces progression of kidney damage. Quality of life was not reported in either trial. The evidence for all outcomes was rated as low- to very low-quality due to trials being at high risk of bias and because there were a small number of trials and a small number of participants included in the trials.