What is sickle cell nephropathy (SCN)?

Updated: Sep 12, 2019
  • Author: Phuong-Thu Pham, MD, FASN; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

Answer

Hemolysis, vaso-occlusion, and ischemia-reperfusion injury are the clinical hallmarks of sickle cell disease (SCD). The renal manifestations of SCD range from various tubular and glomerular functional abnormalities to gross anatomic alterations of the kidneys.

The hypoxic, acidotic, and hyperosmolar environment of the inner medulla are known to promote sickling of red blood cells (RBCs) with resultant impairment in renal medullary blood flow, ischemia, microinfarction, and papillary necrosis. [1] Hematuria commonly occurs due to vascular obstruction and RBC extravasation into the collecting system or due to papillary necrosis.

The underlying mechanisms of renal injury or sickle cell nephropathy (SCN) relate mainly to hypoxia and ischemia. The clinical manifestations are determined by the predominant site of tubular involvement. RBC sickling and congestion in the vasa recta leads to ischemia and associated impairment of solute reabsorption by the ascending limb of the loop of Henle and impairs urinary concentrating ability. More distal tubular dysfunction may impair renal acidification and potassium secretion, leading to an incomplete form of distal renal tubular acidosis and hyperkalemia.  

Patients with SCD generally have lower blood pressure compared with their healthy unaffected counterparts, and hypertension is seen in only 2-6% of patients. [2] The low incidence of hypertension is attributed to reduced vascular reactivity, compensatory systemic vasodilatation associated with microvascular disturbances from sickling of RBCs and thrombotic complications, elevated levels of prostaglandins and nitric oxide, and possibly renal sodium and water wasting associated with suboptimal medullary concentrating activity.  Blood pressures in the range defined as normal for the general population may thus represent hypertension in patients with SCD.

In patients with SCD, supranormal renal hemodynamics—including increased renal blood flow, renal plasma flow, and glomerular filtration rate—occur as early as infancy, but decrease with age. Such alterations in renal hemodynamics lead to increased renal growth and glomerular enlargement. Grossly, the kidneys appear hypertrophied, with a characteristic smooth, capsular surface. [3] Renal function is usually normal during adolescence but frequently becomes subnormal as chronic kidney disease progresses. The kidneys eventually shrink, and the capsular surface becomes grossly distorted and scarred. [3, 4]


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