From the Guidelines
Hemolytic Uremic Syndrome (HUS) is a life-threatening condition characterized by the acute onset of microangiopathic hemolytic anemia, renal injury, and low platelet count, often occurring after an acute gastrointestinal illness, usually diarrhea.
Key Characteristics of HUS
- Microangiopathic hemolytic anemia: characterized by the destruction of red blood cells 1
- Renal injury: often leading to acute renal failure 1
- Low platelet count: thrombocytopenia 1
Causes and Associations
- Shiga toxin-producing Escherichia coli (STEC) infections: a common cause of HUS, particularly STEC O157 1
- Bloody diarrhea: often a precursor to HUS, although approximately 10% of patients with HUS do not have bloody diarrhea 1
- Acute gastrointestinal illness: a common trigger for HUS, usually within 3 weeks after onset of diarrhea 1
Diagnosis and Management
- Laboratory criteria: diagnosis of HUS is based on laboratory criteria, including hemolytic anemia, thrombocytopenia, and renal injury 1
- Monitoring: frequent monitoring of hemoglobin, platelet counts, electrolytes, and blood urea nitrogen and creatinine is recommended to detect early manifestations of HUS 1
- Peripheral blood smear: examining a peripheral blood smear for red blood cell fragments is necessary when HUS is suspected 1
From the Research
Definition of Hemolytic Uremic Syndrome (HUS)
Hemolytic Uremic Syndrome (HUS) is defined by the simultaneous occurrence of nonimmune haemolytic anaemia, thrombocytopenia, and acute renal failure, leading to the pathological lesion termed thrombotic microangiopathy, which mainly affects the kidney, as well as other organs 2. It is a thrombotic microangiopathy characterized by intravascular hemolysis, thrombocytopenia, and acute kidney failure 3.
Types of HUS
There are two primary types of HUS:
- Typical HUS, caused by Shiga toxin-producing Escherichia coli (STEC) infection, often associated with diarrhea 4, 3
- Atypical HUS (aHUS), usually caused by uncontrolled complement activation, not associated with diarrhea 4, 3, 5 Other forms of HUS can occur in the course of systemic diseases or physiopathological conditions, such as pregnancy, after transplantation, or after drug assumption 4.
Pathogenesis of HUS
The pathogenesis of HUS involves endothelial cell injury and platelet activation, although the underlying cause may differ 2. The common pathogenetic features in STEC-HUS, aHUS, and secondary HUS are simultaneous damage to endothelial cells, intravascular hemolysis, and activation of platelets leading to a procoagulative state, formation of microthrombi, and tissue damage 3. Hyperactivation of the complement system is the pathogenetic effector mechanism leading to the endothelial damage and the microvascular thrombosis in aHUS 5.
Clinical Features and Diagnosis
Clinical signs and symptoms may overlap among the different forms of HUS, but pneumococcal-HUS and aHUS have a worse prognosis compared with STEC-HUS 4, 5. Early diagnosis and identification of underlying pathogenetic mechanism allow instating specific support measures and therapies. The diagnosis of HUS is based on the presence of thrombocytopenia, nonimmune microangiopathic hemolytic anemia, and acute renal failure 2, 4, 3, 5.
Treatment and Management
The treatment of HUS depends on the underlying cause and may include supportive care, such as management of electrolyte and water imbalance, anemia, hypertension, and renal failure 4. In patients with aHUS, complement inhibition by eculizumab administration can lead to a rapid and sustained normalization of hematological parameters with improvement in long-term renal function 4, 5. Plasma infusions and plasma exchanges are effective in most cases to treat hemolysis and thrombocytopenia, and a new monoclonal anti-C5 antibody has been tested and seems to be effective in atypical HUS with abnormal complement alternate pathway activation 6.