OVERVIEW

What is Hemolytic Uremic Syndrome?

Hemolytic uremic syndrome (HUS) is a clinical syndrome caused by various etiologies and classified as a thrombotic microangiopathy. It is primarily characterized by microangiopathic hemolytic anemia, acute renal failure, and thrombocytopenia.

It predominantly affects infants, young children, and school-aged children, with over one-third of pediatric HUS cases involving neurological complications.

HUS can be categorized into typical and atypical forms. Typical cases are usually triggered by bacterial infections and often present with preceding gastrointestinal symptoms. Atypical cases frequently have a family history and are prone to recurrence.

HUS has an acute onset, and severe cases can be life-threatening. Symptomatic treatment and plasma exchange can improve survival rates. The disease is non-contagious and does not require isolation.

Is Hemolytic Uremic Syndrome Common?

HUS is uncommon and mostly occurs sporadically.

How Does HUS Differ from Thrombotic Thrombocytopenic Purpura (TTP)?

HUS and TTP share similar clinical manifestations, as both are thrombotic microangiopathies. However, in HUS, microthrombi are confined to the kidneys, whereas TTP can affect multiple organs throughout the body.

TTP is caused by abnormalities in the vWF-cleaving protease (ADAMTS13) and primarily occurs in adults. Most patients exhibit reduced ADAMTS13 activity, with more pronounced systemic symptoms—particularly neurological involvement—and a higher mortality rate.

What Are the Types of Hemolytic Uremic Syndrome?

HUS is classified into two types:

• Typical HUS: Accounts for 90% of cases and is associated with Shiga toxin-producing bacteria (e.g., pathogenic E. coli, Shigella dysenteriae). It often begins with gastrointestinal symptoms like diarrhea, hence also termed post-diarrheal HUS.

• Atypical HUS: Represents ~10% of cases with unclear etiology and no diarrheal symptoms. Possible triggers include bacterial infections, medications, or other underlying conditions.

SYMPTOMS

What clinical manifestations do patients with hemolytic uremic syndrome typically exhibit?

Patients with hemolytic uremic syndrome often present with prodromal infection symptoms and the classic triad of manifestations:

• Prodromal symptoms: 90% of patients experience prodromal symptoms, including diarrhea, abdominal pain, vomiting, and loss of appetite. The prodromal phase typically lasts from a few days to 2 weeks. The disease often manifests suddenly 5–10 days (or up to several weeks) after the prodromal phase.

• Classic triad manifestations:

  • Acute microangiopathic hemolytic anemia: Generalized weakness, jaundice (yellowing of the skin and sclera), dark urine, and pallor.

  • Disseminated intravascular coagulation: Widespread bleeding tendencies, such as skin purpura, hematemesis, melena, hematuria, and conjunctival hemorrhage.

  • Acute renal failure: Reduced urine output, oliguria, or even anuria, accompanied by generalized edema.

Severe cases may develop neurological symptoms, including lethargy, seizures, ataxia, or even coma.

What are the manifestations of mild hemolytic uremic syndrome?

Mild hemolytic uremic syndrome presents only with hemolytic anemia, elevated blood urea nitrogen, and thrombocytopenia.

What are the manifestations of severe hemolytic uremic syndrome?

Severe hemolytic uremic syndrome, in addition to hemolytic anemia, elevated blood urea nitrogen, and thrombocytopenia, is also accompanied by anuria, hypertension, seizures, and other symptoms.

Which tissues and organs are commonly affected by hemolytic uremic syndrome?

Hemolytic uremic syndrome occurs in the microvasculature, primarily affecting the kidneys.

How does hemolytic uremic syndrome typically progress?

Hemolytic uremic syndrome often has an acute onset and progresses rapidly. Classic cases present with symptoms such as diarrhea before the onset, followed by an asymptomatic period before sudden disease manifestation.

What complications are commonly associated with hemolytic uremic syndrome?

Common complications of hemolytic uremic syndrome include:

• Renal insufficiency: Manifested as oliguria, anuria, and azotemia. Some patients may develop chronic renal insufficiency, with irreversible kidney damage even after symptom relief.

• Neurological complications: Lethargy, personality changes, seizures, coma, hemiplegia, ataxia, etc.

• Heart failure: Generalized edema, chest tightness, shortness of breath, and hypertension.

CAUSES

What are the possible causes of hemolytic uremic syndrome?

• Typical hemolytic uremic syndrome is caused by bacterial infections producing verotoxin (such as pathogenic Escherichia coli, Shigella dysenteriae, etc.).

• The cause of atypical hemolytic uremic syndrome is unknown, without diarrhea symptoms, and may be related to bacterial infections, medications, or other diseases.

Which groups are commonly affected by hemolytic uremic syndrome?

Hemolytic uremic syndrome is common in infants, young children, and school-aged children (under 5 years old). Approximately 90% of childhood hemolytic uremic syndrome cases are caused by Escherichia coli infections.

Is hemolytic uremic syndrome contagious?

Hemolytic uremic syndrome is not classified as an infectious disease and is not contagious.

Is hemolytic uremic syndrome hereditary?

The relationship between the causes of hemolytic uremic syndrome and genetics remains unclear, so it is not hereditary.

DIAGNOSIS

How is Hemolytic Uremic Syndrome Diagnosed?

When diagnosing hemolytic uremic syndrome (HUS), doctors primarily rely on clinical manifestations and test results, including microangiopathic hemolytic anemia, thrombocytopenia (platelet count < 150×10⁹/L), and kidney involvement (oliguria, anuria, or significantly elevated creatinine). A family history of similar HUS cases further supports the diagnosis.

What Tests Are Needed for Suspected HUS, and Why?

Common tests include complete blood count (CBC), reticulocyte count, blood biochemistry, urinalysis, coagulation function, Coomb’s test, renal ultrasound, and kidney biopsy:

• CBC: Assesses anemia and thrombocytopenia.
• Reticulocyte count: Evaluates bone marrow function and rules out aplastic anemia.
• Blood biochemistry: Checks kidney function and lactate dehydrogenase levels.
• Urinalysis: Detects hematuria, proteinuria, or urinary tract infections.
• Coagulation function: Assesses clotting disorders.
• Coomb’s test: Differentiates immune-mediated hemolytic anemia.
• Renal ultrasound: Evaluates kidney size and potential thrombosis.
• Kidney biopsy: Performed if diagnosis remains unclear.

What Should Be Noted Before a Kidney Biopsy?

Before the procedure, practice breath-holding and urinating while lying down to facilitate cooperation during/after the biopsy. Post-biopsy, absolute bed rest is required to avoid bleeding risks.

Is a Painful Kidney Biopsy Always Necessary?

Though invasive and slightly painful (tolerable for most), a biopsy carries bleeding risks. It is mainly used to exclude other kidney injuries. If HUS is confirmed, the biopsy may be omitted—consult your physician for a tailored decision.

What Diseases Mimic HUS, and How to Differentiate Them?

Due to nonspecific symptoms (anemia, thrombocytopenia, acute kidney injury), HUS may resemble:

• Thrombotic thrombocytopenic purpura (TTP): Features severe thrombocytopenia, CNS symptoms, fever, and higher mortality. ADAMTS13 deficiency is the cause—confirmed via ADAMTS13 activity testing.
• Systemic lupus erythematosus (SLE): An autoimmune disease with thrombocytopenia and kidney injury; distinguished by antinuclear antibody tests.
• Evans syndrome: Combines autoimmune hemolytic anemia and thrombocytopenia, with a positive Coomb’s test.

TREATMENT

Which department should I visit for hemolytic uremic syndrome?

It is recommended to consult the nephrology department. If hemolytic anemia is the initial symptom, you may also be referred to the hematology department.

Can hemolytic uremic syndrome resolve on its own?

Hemolytic uremic syndrome does not resolve on its own and requires prompt hospital treatment.

How is hemolytic uremic syndrome specifically treated?

• Typical hemolytic uremic syndrome may resolve spontaneously, with treatment primarily focused on symptomatic and supportive care, including maintaining water-electrolyte and acid-base balance, intravenous nutrition, fluid replacement, and blood transfusion.

• Atypical hemolytic uremic syndrome requires plasma exchange, corticosteroids, or immunosuppressive therapy in addition to symptomatic and supportive care. Plasma exchange therapy requires deep venous catheterization and an adequate plasma supply. During corticosteroid and immunosuppressive therapy, the body's resistance may decrease, so infection prevention and protective measures are essential. If symptoms such as oliguria, anuria, hyperkalemia, or progressive elevation of creatinine occur, hemodialysis is necessary, which also requires deep venous catheterization. Once kidney function and urine output recover, the catheter can be removed, and hemodialysis can be discontinued.

Does hemolytic uremic syndrome require hospitalization?

Hemolytic uremic syndrome is a critical condition and requires hospitalization for treatment.

What are the common side effects of medications for hemolytic uremic syndrome?

Commonly used medications for hemolytic uremic syndrome include:

• Corticosteroids may cause infections, osteoporosis, induction or aggravation of peptic ulcers, central obesity, moon face, striae, hypokalemia, diabetes, pancreatitis, and poor wound healing.

• Cyclophosphamide may cause bone marrow suppression, hair loss, gastrointestinal reactions, hemorrhagic cystitis, and cardiotoxicity.

Can hemolytic uremic syndrome be completely cured?

Most patients with hemolytic uremic syndrome can be cured, but a small number may experience irreversible kidney damage and require lifelong dialysis.

DIET & LIFESTYLE

What should patients with hemolytic uremic syndrome pay attention to in their diet?

Patients with hemolytic uremic syndrome should pay attention to dietary hygiene and avoid unclean food. If complicated by renal insufficiency, a low-salt, low-fat, high-quality protein diet is required, with eggs being the most common source of high-quality protein.

What should patients with hemolytic uremic syndrome pay attention to in daily life?

Patients with hemolytic uremic syndrome are advised to wash hands frequently and maintain personal hygiene. Engage in about 30 minutes of daily exercise, combining aerobic and strength training at moderate intensity without overexertion. Ensure adequate sleep each day and practice self-regulation when experiencing high stress or emotional tension.

Do patients with hemolytic uremic syndrome need follow-up examinations after treatment? How?

Individuals who have had hemolytic uremic syndrome are recommended to undergo annual check-ups, including complete blood count, blood biochemistry, urinalysis, and urinary system ultrasound.

Does hemolytic uremic syndrome affect fertility?

Recovery from hemolytic uremic syndrome does not affect fertility.

Can patients with hemolytic uremic syndrome fly, engage in strenuous exercise, or travel to high-altitude areas?

After recovery, patients with hemolytic uremic syndrome can fly, participate in strenuous exercise, and travel to high-altitude regions.

How should family members care for a patient with hemolytic uremic syndrome?

Patients who have recovered from hemolytic uremic syndrome generally do not require special care.

PREVENTION

Can Hemolytic Uremic Syndrome be prevented? How to prevent it?

Typical Hemolytic Uremic Syndrome is associated with bacterial infections. Maintaining personal hygiene, frequent handwashing, and avoiding unclean food can help prevent it to some extent.

How to prevent recurrence of Hemolytic Uremic Syndrome?

For typical Hemolytic Uremic Syndrome, maintaining personal hygiene, frequent handwashing, and avoiding unclean food can help reduce the risk of recurrence.

For atypical Hemolytic Uremic Syndrome, patients should continue oral steroids or immunosuppressants during recovery, gradually tapering the dosage and maintaining a low dose for a period. Do not reduce or stop medication without medical guidance.