Sickle cell nephropathy is a type of nephropathy associated with sickle cell disease which causes kidney complications as a result of sickling of red blood cells in the small blood vessels. The hypertonic and relatively hypoxic environment of the renal medulla, coupled with the slow blood flow in the vasa recta, favors sickling of red blood cells, with resultant local infarction (papillary necrosis). Functional tubule defects in patients with sickle cell disease are likely the result of partial ischemic injury to the renal tubules. Also the sickle cell disease in young patients is characterized by renal hyperperfusion, glomerular hypertrophy, and glomerular hyperfiltration. Many of these individuals eventually develop a glomerulopathy leading to glomerular proteinuria (present in as many as 30%) and, in some, the nephrotic syndrome. Co-inheritance of microdeletions in the -globin gene (thalassemia) appear to protect against the development of nephropathy and are associated with lower mean arterial pressure and less protein in the urine. Mild increases in the blood levels of nitrogen and uric acid can also develop. Advanced kidney failure and high blood urea levels occur in 10% of cases. Pathologic examination reveals the typical lesion of "hyperfiltration nephropathy" namely, focal segmental glomerular sclerosis. This finding has led to the suggestion that anemia-induced hyperfiltration in childhood is the principal cause of the adult glomerulopathy. Nephron loss secondary to ischemic injury also contributes to the development of azotemia in these patients

Pathophysiology
The development of sickle cell nephropathy (SCN) typically occurs in childhood as seen in the appearance of hyperfiltration and proteinuria.
Both are primarily caused by the polymerization of sickle cells in the kidney microvasculature due to the low O2 tension, high osmolarity, and low acidity. This polymerization fills and occludes blood vessels such as the vasa recta in the kidneys leading to microinfarctions, leakage into surrounding tissues and potentially papillary necrosis and renal infarcts. Renal papillae are especially susceptible to damage eventually causing papillary necrosis since these vessels are only supplied with blood by the vasa recta. The sickling of the cells also contribute to two other mechanisms which are chronic hypoxia and chronic hemolysis. Hypoxia is caused from both the insufficient ability for the red blood cells to transport oxygen alongside blood vessel occlusions promoting the activation of Hypoxia Inducible Factor-1𝛂. The hypoxia also causes the over expression of endothelin-1 and functional nitric oxide deficiency and due to the chronic hemolysis, reactive oxygen species are produced leading to vasoconstriction and further medullary hypoxia. This nitric oxide deficiency alongside endothelin-1 overproduction leads to the inability to properly respond to stress and hemodynamic changes which increases the likelihood of experiencing acute kidney injury.The hyperfiltration has multiple contributing factors such as the increased cardiac output caused by the normal physiological response to anemia leading to greater renal blood flow and an increase in glomerular filtration rate (GFR). This is not the only factor because having multiple blood transfusions does not reverse this effect.