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Hemolytic Uremic Syndrome (HUS)

Hemolytic Uremic Syndrome (HUS) is a thrombotic microangiopathy characterized by the triad of microangiopathic hemolytic anemia, thrombocytopenia, and Acute Kidney Injury (AKI). It most commonly occurs after Shiga toxin-producing bacterial infection, particularly in children

ICD-10

D59.3

Specialty

Nephrology

Onset

Acute

Reviewed

August 2026
On This Page

Overview

-Hemolytic Uremic Syndrome (HUS) is a systemic thrombotic microangiopathy causing endothelial injury and formation of small-vessel thrombi.

-The major forms of Hemolytic Uremic Syndrome (HUS) are:

  • Shiga toxin-associated HUS: usually follows diarrheal illness caused by Shiga toxin-producing E. coli or Shigella.
  • Atypical HUS (aHUS): usually results from dysregulation of the alternative complement pathway and may be triggered by infection, pregnancy, medications, or other stressors.

The kidneys are particularly affected, resulting in Acute Kidney Injury (AKI).

Etiology & Risk Factors

-Etiology

–Shiga Toxin-Associated Hemolytic Uremic Syndrome (HUS)

Usually follows infection with:

  • Shiga toxin-producing Escherichia coli (E. coli)
  • Shigella dysenteriae

Shiga toxin causes endothelial injury, particularly in the renal microvasculature.

-Atypical Hemolytic Uremic Syndrome (HUS)

Results from uncontrolled activation of the alternative complement pathway, usually due to genetic or acquired complement abnormalities.

 

-Risk Factors:

  • Recent bloody diarrhea
  • Shiga toxin-producing bacterial infection
  • Young children
  • Complement pathway abnormalities
  • Pregnancy or postpartum state
  • Certain medications
  • Previous episode of aHUS

Pathophysiology

Shiga toxin or complement dysregulation → endothelial injury → platelet activation and microvascular thrombosis → red blood cell fragmentation → microangiopathic hemolytic anemia + thrombocytopenia → renal microvascular injury → reduced GFR → Acute Kidney Injury (AKI)

Clinical Presentation

-Symptoms:

  • loody diarrhea, particularly in typical HUS
  • Abdominal pain
  • Nausea and vomiting
  • Fatigue
  • Pallor
  • Reduced urine output
  • Dark urine
  • Headache
  • Confusion in severe disease

 

-Signs:

  • Pallor
  • Petechiae or bruising
  • Oliguria
  • Edema
  • Hypertension
  • Signs of dehydration following diarrheal illness
Hemolytic Uremic Syndrome (HUS) Overview
Hemolytic Uremic Syndrome (HUS) Overview

History Taking

-Ask about:

  • Recent diarrhea, especially bloody diarrhea
  • Abdominal pain and vomiting
  • Recent food exposure or outbreaks
  • Reduced urine output
  • Dark urine
  • Fatigue and pallor
  • Bleeding or bruising
  • Neurological symptoms
  • Recent infections
  • Medication history
  • Pregnancy or postpartum status

Physical Examination

-General Examination

  • Pallor
  • Blood pressure
  • Hydration status
  • Edema
  • Petechiae or bruising

 

-System-Specific Examination:

  • Abdominal tenderness
  • Assessment of urine output
  • Neurological examination for encephalopathy or seizures
  • Cardiopulmonary examination for fluid overload

Investigations

-Complete Blood Count

Essential for diagnosis:

  • Low platelet count

  • Anemia

 

-Peripheral Blood Film

Important finding:

  • Schistocytes

 

-Biochemistry / Specific Tests

  • Serum creatinine and eGFR

  • Serum urea

  • Serum electrolytes

  • Serum potassium

  • Serum bicarbonate

  • LDH — elevated

  • Haptoglobin — reduced

  • Indirect bilirubin — elevated

  • Reticulocyte count — elevated

  • Direct antiglobulin test — usually negative

  • Urinalysis

  • Urine protein assessment

 

-Specific microbiological testing:

  • Stool culture

  • Shiga toxin testing or molecular assay when appropriate

 

-Imaging

Not routinely required for diagnosis.

Renal ultrasound may be used when assessing kidney size, obstruction, or other complications.

 

-Special / Confirmatory Tests

  • Shiga toxin testing for suspected infection-associated HUS

  • Complement studies in suspected atypical HUS

  • Genetic testing for complement pathway abnormalities when appropriate

ADAMTS13 activity should be urgently assessed when thrombotic thrombocytopenic purpura (TTP) is a significant differential diagnosis.

Diagnosis

-Diagnosis of Hemolytic Uremic Syndrome (HUS) is based on the characteristic combination of:

Microangiopathic hemolytic anemia + thrombocytopenia + Acute Kidney Injury (AKI)

-Supportive findings include:

  • Schistocytes
  • Elevated LDH
  • Low haptoglobin
  • Increased indirect bilirubin
  • Increased creatinine
  • Proteinuria or hematuria
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Management

1. First-Line / Emergency Management

  • Urgent hospital admission

  • Careful fluid and electrolyte management

  • Treat severe hyperkalemia

  • Manage severe hypertension

  • Treat pulmonary edema

  • Initiate dialysis when indicated

  • Monitor neurological and cardiovascular complications

 

2. Definitive Treatment

Shiga Toxin-Associated HUS

Treatment is primarily supportive:

  • Maintain appropriate fluid and electrolyte balance

  • Manage Acute Kidney Injury (AKI)

  • Dialysis when required

  • Manage hypertension and complications

-Atypical HUS

Complement inhibition with eculizumab or ravulizumab is the key disease-specific treatment when aHUS is diagnosed or strongly suspected.

 

3. Medical Treatment

  • Careful IV fluid management according to volume status

  • Antihypertensive therapy

  • Red blood cell transfusion when clinically indicated

  • Dialysis for severe kidney failure or standard indications

  • Eculizumab or ravulizumab for appropriate patients with aHUS

Routine platelet transfusion is generally avoided unless there is significant bleeding or an invasive procedure requiring it.

 

4. Surgical / Procedural Treatment

No routine surgical treatment.

Renal replacement therapy may be required for severe Acute Kidney Injury (AKI).

 

5. Supportive Management

  • Strict fluid balance

  • Monitor urine output

  • Frequent electrolyte monitoring

  • Monitor platelet count and hemolysis markers

  • Control blood pressure

  • Avoid nephrotoxic medications

Complications

  • Severe Acute Kidney Injury (AKI)
  • Kidney failure
  • Hyperkalemia
  • Metabolic acidosis
  • Hypertension
  • Fluid overload
  • Pulmonary edema
  • Neurological complications
  • Seizures
  • Encephalopathy
  • Thrombosis
  • Pancreatitis

Prognosis

Most children with Shiga toxin-associated Hemolytic Uremic Syndrome (HUS) recover with appropriate supportive care, although severe cases may require temporary dialysis. A proportion develop persistent hypertension, proteinuria, or Chronic Kidney Disease (CKD). Atypical HUS has a higher risk of recurrence and progressive kidney failure without appropriate complement-targeted treatment.

Key Points / Clinical Pearls

  • Hemolytic Uremic Syndrome (HUS) is a thrombotic microangiopathy.
  • The classic triad is microangiopathic hemolytic anemia, thrombocytopenia, and Acute Kidney Injury (AKI).
  • Shiga toxin-producing E. coli is the most common cause of typical HUS.
  • HUS often follows a diarrheal illness, particularly bloody diarrhea.
  • Shiga toxin causes endothelial injury and microvascular thrombosis.
  • Schistocytes are an important peripheral blood film finding.
  • LDH is elevated and haptoglobin is typically reduced.
  • Stool testing can identify Shiga toxin-producing organisms.
  • ADAMTS13 testing helps distinguish HUS from TTP.
  • Atypical HUS results from dysregulation of the alternative complement pathway.
  • Severe cases may develop hyperkalemia, metabolic acidosis, hypertension, and fluid overload.
  • Supportive treatment is the mainstay for Shiga toxin-associated HUS.
  • Dialysis may be required for severe Acute Kidney Injury (AKI).