Clinical meaning
Hemolytic uremic syndrome (HUS) is a life-threatening condition characterized by a triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. The most common form, typical HUS, is triggered by infection with Shiga toxin-producing Escherichia coli (STEC), particularly serotype O157:H7. This bacterium colonizes the intestinal mucosa and releases Shiga toxin (Stx), which enters the bloodstream and binds to globotriaosylceramide (Gb3) receptors concentrated on the surface of renal glomerular endothelial cells. Once internalized, Shiga toxin inhibits protein synthesis by cleaving ribosomal RNA, causing direct endothelial cell injury and death. The damaged endothelium triggers a cascade of thrombotic microangiopathy: platelets aggregate on the injured vascular surfaces forming microthrombi within small arterioles and capillaries, particularly in the renal glomeruli. These microthrombi partially occlude the vessel lumen, creating turbulent blood flow that mechanically shears red blood cells as they pass through the narrowed vessels, producing fragmented red blood cells called schistocytes. This mechanical destruction of red blood cells is the hallmark of microangiopathic hemolytic anemia. The platelet consumption in forming microthrombi leads to thrombocytopenia, while the occlusion of renal microvessels produces ischemic injury to the glomeruli and tubules, resulting in acute kidney injury with oliguria or anuria. In children, HUS is the most common cause of acute kidney injury requiring dialysis. Atypical HUS (aHUS) is a distinct condition caused by dysregulation of the complement system, specifically uncontrolled activation of the alternative complement pathway due to genetic mutations in complement regulatory proteins such as factor H, factor I, or membrane cofactor protein. This complement-mediated form causes ongoing endothelial damage without a preceding STEC infection and tends to relapse. Treatment for aHUS includes eculizumab (Soliris), a monoclonal antibody that blocks C5 cleavage and terminal complement activation. The practical nurse must recognize the HUS triad, monitor renal function closely, implement strict intake and output measurement, and understand that antibiotic use during STEC infection is contraindicated as it can increase Shiga toxin release and worsen HUS risk.