The kidney in sickle cell anemia.

New insights into the physical chemistry and molecular epidemiology of sickle cell anemia have improved our understanding of the pathophysiology of the associated nephropathy, the predictors of this complication, and genetic and other factors that may modify it. In this article, we analyze the current clinicopathologic knowledge with reference to the predilection to nephropathy and the protection from hypertension, as well as the altered renal physiology of the sickle cell state that underlies both these phenomena. In the early stages of sickle cell anemia, the kidney is characterized by impaired function of the renal medulla, as evidenced by reduced capacity to concentrate, acidify, and excrete potassium into the urine. Meanwhile, the cortex functions supranormally, as evidenced by increased renal plasma flow and glomerular filtration rate, proximal tubular function, and urinary diluting capacity. In addition to the complications of hematuria and papillary necrosis, renal insufficiency supervenes in a subgroup of patients. The morphology of the glomerulopathy generally differs between children and adults; in the latter group there is a particularly poor prognosis and markedly shortened life expectancy. Renal replacement therapy has nonetheless been successful. Although hypertension may be found at this stage, it is extremely rare before the onset of significant renal impairment. The possible mechanism of this protection is discussed, with a focus on the compelling need for further investigation in light of the newly gained basic understanding of this hematorenal syndrome.