Hyperkalemia and Metabolic Acidosis Occur at a Higher eGFR in Sickle Cell Disease

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.

Importance of Metabolic Acidosis as a Health Risk in Chronic Kidney Disease

Human kidneys are well adapted to excrete the daily acid load from diet and metabolism in order to maintain homeostasis. In approximately 30% of patients with more advanced stages of CKD, these homeostatic processes are no longer adequate, resulting in metabolic acidosis. Potential deleterious effects of chronic metabolic acidosis in CKD, including muscle wasting, bone demineralization, hyperkalemia, and more rapid progression of CKD, have been well cataloged. Based primarily upon concerns related to nutrition and bone disease, early Kidney Disease Outcomes Quality Initiative guidelines recommended treating metabolic acidosis with alkali therapy targeting a serum bicarbonate ≥22 mEq/L. More recent guidelines have suggested similar targets based upon potential slowing of CKD progression. However, appropriately powered, long-term, randomized controlled trials to study efficacy and safety of alkali therapy for these outcomes are largely lacking. As a result, practice among physicians varies, underscoring the complexity of treatment of chronic metabolic acidosis in real-world CKD practice. Novel treatment approaches and rigorous phase 3 trials may resolve some of this controversy in the coming years. Metabolic acidosis is an important complication of CKD, and where it "falls" in the priority schema of CKD care will depend upon the generation of strong clinical evidence.