Hemolytic uremic syndrome (HUS) !

HUS is a serious complication, mostly in young children after bloody diarrhoea, in which tiny clots damage the kidneys, destroy red cells and use up platelets.

Updated 2026-11-01

Structures involved

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Microorganisms that cause it

Why it happens

What it is

A thrombotic microangiopathy defined by the triad of microangiopathic haemolytic anaemia, thrombocytopenia and acute kidney injury. The typical form follows bloody diarrhoea caused by Shiga toxin-producing Escherichia coli (STEC) and is the leading cause of acute kidney failure in young children.

Who gets it

Mostly affects children under 5 years. Up to about 1 in 10 people with STEC infection develop HUS. Argentina has one of the highest childhood rates in the world and treats it as a notifiable public-health problem; in Colombia and the rest of Latin America it is less often reported, but STEC from undercooked beef, raw milk and unsafe water is a recognised risk. Atypical (complement-mediated) HUS is rare and can occur at any age.

Causes

Typical (STEC-HUS, about 90% of children): Shiga toxin-producing E. coli, classically serotype O157:H7; less often Shigella dysenteriae type 1
Pneumococcal HUS: invasive Streptococcus pneumoniae infection (pneumonia with empyema, meningitis)
Atypical HUS: genetic or acquired dysregulation of the alternative complement pathway (e.g. factor H, factor I or MCP variants, anti-factor H antibodies)
Secondary causes: some drugs (calcineurin inhibitors, some chemotherapy agents), transplantation, pregnancy, malignant hypertension, cobalamin C defect

Risk factors

Age under 5 years (and older adults) with STEC infection
Eating undercooked ground beef, raw (unpasteurised) milk or dairy, contaminated raw vegetables or sprouts
Drinking or swimming in unsafe water; contact with farm animals
Person-to-person spread in households and day-care centres
Use of antibiotics or antimotility drugs during STEC diarrhoea, which is associated with a higher risk of HUS
Family history of HUS (atypical form)

Pathophysiology

STEC colonises the colon and releases Shiga toxin, which crosses into the blood and binds the Gb3 receptor, abundant on glomerular endothelium. The toxin halts protein synthesis and injures endothelial cells, triggering platelet-rich microthrombi in small vessels of the kidney (and sometimes brain, gut and pancreas). Red cells are sheared as they pass the damaged vessels (schistocytes), platelets are consumed, and reduced glomerular blood flow causes acute kidney injury. In atypical HUS, uncontrolled complement activation produces the same endothelial damage without an infection trigger.

Classification

Typical HUS: STEC-associated, preceded by diarrhoea (D+ HUS)
Pneumococcal HUS: neuraminidase exposes the Thomsen-Friedenreich antigen; direct Coombs test often positive
Atypical HUS: complement-mediated, no diarrhoeal prodrome, relapsing course
Secondary HUS: drugs, transplantation, pregnancy, systemic disease

Symptoms and signs

Prodrome of abdominal cramps and diarrhoea, often bloody, with little or no fever
About 5 to 10 days after the diarrhoea starts: sudden pallor, tiredness and irritability
Reduced urine output or no urine (oliguria or anuria), sometimes dark or bloody urine
Swelling (oedema) and high blood pressure
Petechiae or bruising from low platelets, usually without major bleeding
Mild jaundice; enlarged liver or spleen on examination

Diagnosis

Clinical: Suspected in a child with recent bloody diarrhoea who becomes pale, swollen and passes little urine. The examination checks hydration, blood pressure, weight, oedema, petechiae, abdominal signs and neurological status.
Tests: Complete blood count: anaemia and platelets below 150,000/µL. Peripheral smear with schistocytes. Haemolysis markers: high LDH and indirect bilirubin, low haptoglobin, raised reticulocytes; direct Coombs test negative (positive in pneumococcal HUS). Coagulation times usually normal, which helps separate it from DIC. Rising creatinine and urea, electrolytes (hyperkalaemia, acidosis), urinalysis with haematuria and proteinuria. Stool culture and testing for Shiga toxin or its genes (PCR). In atypical cases: complement C3, ADAMTS13 activity to exclude TTP, and genetic studies.
Imaging: Not required for diagnosis. Kidney ultrasound may show enlarged, echogenic kidneys and rules out obstruction; abdominal ultrasound assesses colitis or intussusception; brain MRI if there are neurological signs.

Differential diagnosis

Thrombotic thrombocytopenic purpura (ADAMTS13 activity below 10%, more neurological signs, mostly adults)
Disseminated intravascular coagulation (prolonged coagulation times, low fibrinogen)
Immune thrombocytopenia or Evans syndrome (no kidney injury; Coombs positive in Evans)
Acute kidney injury from dehydration in gastroenteritis (no haemolysis or schistocytes)
Intussusception, inflammatory bowel disease or bacterial dysentery as causes of bloody diarrhoea
Sepsis, malignant hypertension and systemic lupus erythematosus

Goal of treatment

Support the patient through the acute phase: keep fluid and electrolyte balance, correct severe anaemia, control blood pressure, replace kidney function when needed and detect extrarenal complications early, while avoiding interventions that may worsen the disease.

Treatment

Acute: Supportive care in hospital, often in a paediatric unit with access to dialysis. Early isotonic intravenous fluids during STEC diarrhoea may protect the kidneys; once oliguria sets in, fluids are restricted and matched to losses.
Acute: Red cell transfusion for severe anaemia. Platelet transfusion is generally avoided unless there is active bleeding or a procedure, because it may add to microthrombi.
Procedure: Kidney replacement therapy (peritoneal dialysis or haemodialysis) for anuria, refractory hyperkalaemia, acidosis, fluid overload or uraemia.
Medical: Antihypertensive drugs for high blood pressure. In STEC diarrhoea, antibiotics and antimotility agents are generally avoided. Atypical HUS is treated with complement C5 inhibitors (such as eculizumab); plasma exchange is used when TTP or complement disease is suspected and the inhibitor is not available.
Follow-up: Nursing priorities: strict intake and output, daily weight, frequent blood pressure, neurological checks, electrolytes and blood counts; contact precautions and hand hygiene to prevent spread to others.

Complications

Need for acute dialysis (about half of children with typical HUS)
Chronic kidney disease, proteinuria and hypertension years later
Seizures, coma or stroke from central nervous system involvement
Haemorrhagic colitis with bowel necrosis, perforation or later strictures
Pancreatitis and diabetes mellitus; heart involvement (myocardial dysfunction)
Fluid overload, pulmonary oedema and life-threatening hyperkalaemia
Death, mostly in the acute phase

Prognosis

Most children with typical HUS recover kidney function with good supportive care, but acute mortality is around 3 to 5% and up to a quarter keep long-term sequelae (proteinuria, hypertension, reduced kidney function), so follow-up for years is advised. Atypical HUS tends to relapse and had a poor outlook before complement inhibitors.

Prevention

Cook ground meat thoroughly until it is no longer pink inside
Drink and use only pasteurised milk and dairy products
Handwashing with soap after using the toilet or changing nappies and before preparing food
Separate raw and cooked food, safe drinking water and washed vegetables
Exclusion of affected children from day care until stool tests are negative, as set by local public-health rules

Test yourself

Think of the answer, then tap the question to see it.

What is the classic triad of hemolytic uremic syndrome?

Microangiopathic haemolytic anaemia (with schistocytes), thrombocytopenia and acute kidney injury.

Which organism and toxin cause most childhood HUS?

Shiga toxin-producing E. coli, classically O157:H7, usually after bloody diarrhoea from undercooked beef or raw milk.

Which test result helps distinguish HUS from DIC?

In HUS the coagulation times (PT, aPTT) and fibrinogen are usually normal; in DIC they are abnormal.

How is HUS distinguished from TTP?

TTP has severely reduced ADAMTS13 activity (below 10%), occurs mostly in adults and has more neurological involvement; HUS shows more severe kidney injury.

Why are antibiotics and antimotility drugs generally avoided in STEC diarrhoea?

They are associated with greater toxin release or absorption and a higher risk of progressing to HUS.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Hemolytic-uremic syndrome (MedlinePlus Medical Encyclopedia (U.S. National Library of Medicine), 2026); E. coli (World Health Organization, 2018); Síndrome urémico hemolítico - SUH - (Ministerio de Salud de la Nación (Argentina), 2026).

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Representative model, for educational purposes only.

Kidneys highlighted on the Durgical 3D model