Hemolytic-uremic syndrome

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Hemolytic-uremic syndrome

Hematological system

Hematological system

Hematological system

Hematological system


Hemolytic-uremic syndrome


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USMLE® Step 1 questions

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Hemolytic-uremic syndrome

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USMLE® Step 1 style questions USMLE

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A 9-year-old boy is brought to the emergency department by his parents due to prolonged bleeding following a tooth extraction earlier in the day. Past medical history is noncontributory. Temperature is 37.5°C (99.5°F), pulse is 88/min, respirations are 14/min, and blood pressure is 112/62 mmHg. Physical exam shows gingival bleeding and petechiae. Laboratory testing is obtained, and the results are shown below.  
Laboratory value  Result
 Hemoglobin  12 g/dL 
 Hematocrit  40% 
 Platelet count  95,000/mm3  
 Leukocyte count  9,000/mm3  
Coagulation studies  
 Prothrombin time (PT)  12 seconds 
 Activated partial thromboplastin time (aPTT)  29 seconds 
 Bleeding time*  15 minutes 
*Reference Range: 2-7 minutes  

Which of the following conditions is the patient at greatest risk of developing?   

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Enterohemorrhagic Escherichia coli (EHEC) p. 130, 143, 176

hemolytic-uremic syndrome p. 434

Hemolytic-uremic syndrome (HUS)

Escherichia coli p. , 143, 176

exotoxins p. 130

platelet disorders p. 434

schistocytes in p. 424

Pediatric patients

hemolytic-uremic syndrome p. 434


‘Hemo’ refers to the blood, ‘lytic’ refers to breaking down, and ‘uremic’ refers to increased urea levels in the blood.

And this helps explain hemolytic uremic syndrome because the two main effects are destruction of red blood cells and the declining function of the kidney causing uremia - both of which result from tiny blood clots that form in tiny blood vessels - predominantly in the kidneys.

Classically, especially in children, hemolytic uremic syndrome is triggered by a bout of bloody diarrhea.

When that happens, it’s called diarrhea-positive or D positive hemolytic syndrome, sometimes shortened to HUS or simply typical HUS.

Escherichia coli or E. coli is usually the culprit, and children often pick it up through contaminated food or drink, like contaminated beef or unpasteurised milk from an infected cow.

The particular strain of E.coli responsible for hemolytic uremic syndrome is known as enterohemorrhagic E. coli or EHEC, serotype O157:H7.

These numbers and letters refer to the specific antigens on the surface of the bacteria.

‘157’ refers to the O-antigen present in the lipopolysaccharide cell wall and ‘7’ refers to the H-antigen located on the flagella of the bacteria.

Other strains of E. coli as well as other bacteria can also cause hemolytic uremic syndrome, but E. coli O157:H7 is the most common culprit.

After entering the digestive tract, E. coli O157:H7 attaches to the intestinal wall and secretes a toxin called Shiga-like toxin.

The toxin gets its name due to its structural similarity with shiga toxin produced by Shigella dysenteriae, another bacteria that causes bloody diarrhea and subsequent hemolytic uremic syndrome.

So that toxin gets absorbed by intestinal blood vessels and is then picked up by immune cells like eosinophils, basophils and neutrophils.

From there, the toxin is carried on the surface of these cells to the site of blood filtration - which is the glomerular capillaries of the kidney.


Hemolytic-uremic syndrome (HUS) is a serious condition that's characterized by microangiopathic hemolytic anemia, thrombocytopenia, and renal failure. It is usually caused by E. coli O157:H7 infection and presents with fever, jaundice, stomach cramps, vomiting, and diarrhea. A person with HUS may also have a rash, red or purple dots on the skin, and tiredness.


  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Pathogenesis of Atypical Hemolytic Uremic Syndrome" Journal of Atherosclerosis and Thrombosis (2019)
  6. "Shiga Toxin-Associated Hemolytic Uremic Syndrome: A Narrative Review" Toxins (2020)
  7. "Pediatric Atypical Hemolytic Uremic Syndrome Advances" Cells (2021)

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