Functional tubule abnormalities such as nephrogenic diabetes insipidus result from marked reduction in vasa recta blood flow, combined with ischemic tubule injury and sickled erythrocytes in the vasa recta of the inner medulla impairing free water absorption, all causing the production of dilute urine. The concentrating defect also occurs in individuals with sickle trait. This can lead to symptoms such as polyuria and dehydration due to the low water reabsorption.Increase risk of urinary tract infection from encapsulated bacteria due to hyposplenism from spontaneous infarctions in the spleen (autosplenectomy). Additionally, papillary necrosis can increase the risk of a UTI and all infections should be dealt with promptly to prevent sickle cell crisis.Initially, hyperfiltration occurs in pediatrics and then after 30 years old, the GFR slowly declines which is proportional to the development of proteinuria. Worsening proteinuria is gradual, but a sudden onset could have a secondary cause such as nephritic syndrome from FSGS or minimal change disease, membranoproliferative glomerulonephritis, or hepatitis C.Tubular dysfunction, specifically incomplete distal renal tubular acidosis, is caused by the impaired potassium and hydrogen excretion as well as the impaired bicarbonate reabsorption. These contribute to the development of metabolic acidosis, high blood potassium and defects in uric acid excretion which, combined with increased purine synthesis in the bone marrow, results in high blood uric acid levels.Renal infarcts from total occlusion which can present with pain, vomiting, fever, and high blood pressure. Complications
Kidney complications of sickle cell disease include cortical infarcts leading to loss of function, persistent bloody urine, and perinephric hematomas.
The other contributor is glomerular hypoxia in that it releases local prostaglandins: a potent vasodilator, and nitric oxide synthase which increases renal blood flow and therefore GFR. Hemolysis also plays a role in hyperfiltration through the release of heme oxygenase-1 (HO-1) in response to kidney injury and this enzyme converts heme to biliverdin with the by-product being carbon monoxide. Biliverdin and carbon monoxide both act as antioxidants and carbon monoxide also acts as a vasorelaxant, and this causes an increase in GFR. A consistent increase in GFR can lead to proteinuria, glomerulosclerosis, and can eventually worsen progressive chronic kidney disease (CKD).Albuminuria is caused by microvascular damage in the kidneys, hemolysis and endothelial dysfunction. From the increased GFR and the ischemic injury caused by the polymerization of sickle cells, scar tissue develops in the glomeruli which reduces the ability of the glomerulus to properly filter proteins leading to proteinuria. The chronic hemolysis causes the release of iron and free hemoglobin in the kidneys. The iron builds up and leaves deposits in the kidneys, and this causes the overproduction of mesangial cells eventually leading to interstitial and glomerular fibrosis. The free plasma hemoglobin contains cytotoxic heme groups which damage renal tubular epithelial cells and the hemoglobin ends up in the filtrate causing hemoglobinuria. Though the hemoglobin can be reabsorbed in the proximal tubules through binding cubilin and megalin, in doing so it competes with albumin, so the build up of hemoglobin in the filtrate reduces albumin resorption which can worsen albuminuria.