Curriculum · Hematology
Haemolytic uraemic syndrome
What it is
Hemolytic uremic syndrome is a triad of microangiopathic hemolytic anemia, thrombocytopenia and acute renal failure. It is common in children after E. coli 0157:H7 infection, which makes a Shiga-like toxin. Three types are named: typical HUS from Shiga toxin, atypical HUS which is complement-mediated, and secondary HUS. In the scheme of acute kidney injury it belongs to intrinsic renal failure, which is most commonly acute tubular necrosis and less commonly acute glomerulonephritis, and hemolytic uremic syndrome is given there as an example.
Causes and risk
The infection is often from undercooked beef. Shiga toxin damages the endothelium; platelets adhere and microthrombi form; red cells fragment as they pass through and become schistocytes; and the microthrombi block renal vessels, so acute kidney injury follows. In short, endothelial injury gives microthrombi, which give RBC destruction and a fall in platelets. Atypical HUS is complement-mediated. Secondary HUS follows some other cause, including a drug.
How it presents
It is preceded by bloody diarrhea, and in children that is the usual opening. Then come:
- Pallor, lethargy and irritability
- Hypertension from renal involvement
- Seizures or encephalopathy in severe cases
Two worked cases show how far apart the ages can be. A previously healthy 5-year-old girl is brought to ER with bloody diarrhea, pallor, and fatigue; her heart rate is 130 with a blood pressure of 145/101; on examination she is irritable with dry mucous membranes; and her laboratory data show a WBC of 17,000, hemoglobin of 8, platelet count of 65, BUN of 25, and creatinine of 282 umol/L. A young male with a previous episode of bloody diarrheal illness presents with fatigue, lightheadedness, gum bleeding and dark urine, and on examination is pale, jaundiced and with scattered bruising. Note what the second case adds: the jaundice and dark urine of hemolysis, and the gum bleeding and bruising of a low platelet count.