Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Haemolytic uraemic syndrome
Paediatrics and child health · UK scope · Sources checked 27 Aug 2026 · Clinical review pending
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Evolving multisystem thrombotic microangiopathy
Pallor, bruising, reduced urine, oedema, hypertension, confusion, seizure or severe abdominal pain after diarrhoea can indicate HUS. Hyperkalaemia, pulmonary oedema, severe hypertension, neurological involvement and anuria are immediate threats.
Action: Admit urgently and contact paediatric nephrology. Establish strict fluid balance and twice-daily weight, obtain FBC, film, haemolysis markers, renal profile, blood gas, glucose and stool or rectal testing labelled suspected STEC/HUS. Treat seizures, hyperkalaemia, shock and pulmonary oedema through paediatric protocols and arrange dialysis assessment without waiting for the complete triad.
Overview
Recognise thrombotic microangiopathy after bloody diarrhoea, confirm haemolysis, thrombocytopenia and kidney injury, avoid harmful antimicrobials and antimotility drugs in suspected STEC, and escalate early for renal and neurological support.
STEC-HUS, previously called typical or diarrhoea-associated HUS, is the leading form in children. Shiga toxin from contaminated food, water, animal contact or person-to-person spread enters the circulation after gastrointestinal infection.
The toxin binds susceptible microvascular endothelium, especially in renal glomeruli, and triggers swelling, inflammation and platelet-rich microthrombi. Red cells fragment across narrowed vessels and platelets are consumed.
The gastrointestinal prodrome often begins with cramping and watery diarrhoea, which may become bloody. HUS usually develops after the bowel illness has started, when diarrhoea may appear to improve and families think the infection is ending.
Ask about urine output and colour, fluid intake, vomiting, weight, pallor, bruising, irritability, headache, vision, seizures and breathlessness. Record farm or animal exposure, undercooked minced meat, unpasteurised products, raw produce, travel and contacts with diarrhoea.
Practice
Two practice questions
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Paediatrics and child healthOriginal SBA
Bloody diarrhoea prescribing
A 3-year-old has severe abdominal cramps and bloody diarrhoea after a farm visit. The child is stable and STEC is suspected. Which medication approach is most appropriate?
Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources
Sources and review status
National guidance is shown before implementation-dependent detail. Apply principles in context and verify current guidance when a decision affects care. Source check completed 27 Aug 2026; clinical approval remains outstanding.
Examine perfusion and hydration before prescribing fluid, then assess oedema, blood pressure, respiratory status, abdominal tenderness, hepatosplenomegaly, skin bleeding and neurological function. Children can move from dehydrated to overloaded as filtration falls.
Haemolysis produces falling haemoglobin, schistocytes, raised LDH and unconjugated bilirubin, low haptoglobin and reticulocytosis, although marrow response can lag. Platelets are commonly reduced but serious spontaneous bleeding is less common than the count implies.
AKI ranges from mild creatinine elevation to anuria. Potassium, acid-base balance and fluid state can change quickly, so serial results and measured urine are more useful than a single admission panel.
Coagulation tests are often near normal in HUS, unlike disseminated intravascular coagulation. Fever, shock, prolonged clotting, very low fibrinogen and widespread bleeding increase concern for sepsis-associated consumption.
Supportive fluid management requires a phase-specific approach. Early isotonic rehydration may protect renal perfusion in a depleted child, but once oliguria or anuria is established, unmeasured maintenance fluid can cause pulmonary oedema and hypertension.
Complement-mediated atypical HUS can follow infection but is driven by uncontrolled alternative-complement activation. Absence of diarrhoea does not prove atypical disease, and preceding diarrhoea does not absolutely exclude it; recurrent, familial or unexplained cases need complement and genetic investigation.
Eculizumab or ravulizumab is specialist therapy for complement-mediated aHUS after urgent exclusion and prevention of meningococcal infection. It is not routine treatment for confirmed STEC-HUS.
Most STEC-HUS children recover, including many who need temporary dialysis. Long-term risks include hypertension, proteinuria and reduced kidney function, so discharge planning includes renal follow-up even after blood counts normalise.
Key points
HUS is the triad of microangiopathic haemolytic anaemia, thrombocytopenia and acute kidney injury; the components may evolve sequentially rather than appear together.
Most childhood UK cases follow Shiga toxin-producing E. coli gastroenteritis, often abdominal pain and diarrhoea that becomes bloody several days before pallor and oliguria.
Send stool or, if unavailable, a rectal swab labelled suspected STEC or HUS for culture and toxin/PCR testing; a negative late sample does not exclude the syndrome.
First-line blood tests are FBC with serial platelets, blood film for schistocytes, reticulocytes, bilirubin, LDH, haptoglobin, creatinine, electrolytes, bicarbonate, glucose and coagulation screen.
A direct antiglobulin test is usually negative in microangiopathic haemolysis and helps distinguish immune haemolytic anaemia when the picture is uncertain.
Do not give antibiotics for suspected STEC gastroenteritis unless infection specialists identify a separate compelling indication; UKHSA warns they may increase HUS risk.
Do not use loperamide or other antimotility agents in suspected STEC or bloody diarrhoea because toxin and organism retention may worsen disease.
First-line treatment is meticulous supportive care: careful volume assessment, measured isotonic replacement before oliguria when depleted, then input matched to losses once AKI develops.
Aetiology
01
Shiga toxin infection
STEC acquired through contaminated food, water, animals, soil or close contact causes most childhood HUS episodes.
02
Complement dysregulation
Pathogenic variants or antibodies affecting alternative-complement control produce recurrent or severe atypical HUS, sometimes after an infection trigger.
03
Secondary microangiopathy
Pneumococcal infection, medicines, transplantation, autoimmune disease and malignant hypertension can produce a related secondary thrombotic microangiopathy syndrome.
Pathophysiology
1
Endothelial toxin injury
Absorbed Shiga toxin damages susceptible small-vessel endothelium, particularly within the renal glomerular capillary beds of children.
2
Platelet microthrombi
Activated endothelium recruits and consumes circulating platelets, creating widespread microvascular thrombi that obstruct organ perfusion and function.
3
Mechanical red-cell fragmentation
Erythrocytes crossing narrowed fibrin-rich vessels shear into circulating schistocytes, causing progressive non-immune intravascular haemolytic anaemia in children.
4
Renal microvascular ischaemia
Glomerular and arteriolar obstruction reduces filtration, causing oliguria, salt retention, hypertension and progressive uraemic biochemical disturbance.
5
Complement amplification
Alternative-complement activation intensifies microvascular endothelial injury, especially in genetically susceptible children with severe complement-mediated atypical disease.
Clinical features and red flags
Diarrhoeal sequence
Identify abdominal cramps, watery then bloody diarrhoea followed days later by pallor, bruising, oedema or reduced urine.
Haemolytic phenotype
Look for pallor, jaundice, tachycardia and dark urine, then confirm falling haemoglobin and fragmented cells.
Platelet consumption
Petechiae or bruising may occur, but thrombocytopenia is often found through serial FBC before major bleeding.
Renal deterioration
Trend weight, urine output, pressure, creatinine, potassium, bicarbonate and respiratory state at short intervals.
Neurological involvement
Repeat alertness, behaviour, headache, vision and seizure assessment because CNS disease can evolve quickly.
Atypical-HUS clues
Consider recurrence, family history, no STEC evidence, disproportionate severity, complement abnormality or incomplete recovery.
Red flags requiring action
Reduced urine, rising weight, oedema, hypertension or breathlessness after bloody diarrhoea suggests evolving AKI and fluid overload.
Marked pallor, jaundice, petechiae or bruising with falling haemoglobin and platelets indicates active microangiopathic haemolysis.
Irritability, confusion, seizure, focal deficit or reduced consciousness
Investigations
01First-line: serial FBC and blood filmFirst stepFirst line
Why
Detect anaemia, thrombocytopenia and fragmented red cells as the triad evolves.
Interpretation and limitations
Schistocytes with falling haemoglobin and platelets supports microangiopathy; one early normal count does not exclude later HUS.
Raised LDH and unconjugated bilirubin, low haptoglobin and reticulocytosis support haemolysis; direct antiglobulin testing is usually negative.
03Renal profile, gas and urinalysis
Why
Grade AKI, electrolyte, acid-base and urinary consequences.
Interpretation and limitations
Rising creatinine, potassium or weight and falling urine output determine monitoring and dialysis urgency.
04Reference infection test: stool or rectal STEC assay
Why
Detect Shiga toxin genes and culture the outbreak organism for public-health action.
Interpretation and limitations
Label suspected STEC or HUS explicitly; a negative late result does not exclude a compatible clinical syndrome.
05Complement, ADAMTS13 and genetic testing
Differential diagnosis
01
Sepsis with DIC
Shock, prolonged clotting, low fibrinogen and diffuse bleeding favour disseminated coagulation, although sepsis and HUS can overlap.
02
Thrombotic thrombocytopenic purpura
Severe ADAMTS13 deficiency causes thrombotic microangiopathy with prominent neurological disease and relatively less renal-predominant organ injury.
03
Acute glomerulonephritis
Glomerular haematuria, oedema and hypertension without fragmented haemolysis or platelet consumption suggests an inflammatory nephritic disease process.
04
Immune haemolytic anaemia
A positive direct antiglobulin test, circulating spherocytes and preserved platelets support antibody-mediated red-cell destruction rather than microangiopathy.
05
IgA vasculitis
Palpable purpura with normal platelets, joint symptoms and abdominal pain distinguishes small-vessel vasculitis from consumptive microangiopathy.
Management
01Bloody diarrhoeaIdentify children at HUS riskFirst stepA child has severe or bloody diarrhoea, especially under age 5 years.+
1Send stool or rectal swab explicitly labelled suspected STEC and assess hydration, blood pressure, weight and urine output.
2Obtain baseline FBC, film and renal profile when admitted, systemically unwell or clinically concerning, then arrange serial review.
3Avoid antibiotics and antimotility medicines unless a separate specialist-defined indication overrides the STEC risk.
02Evolving triadEscalate before all components appearEscalationAnaemia, thrombocytopenia or AKI develops after diarrhoeal illness.+
1Admit and contact paediatric nephrology, notify the health protection team and institute enteric precautions.
2
Complications
01
Severe acute kidney injury
Oliguria and anuria produce hyperkalaemia, acidosis, uraemia, hypertension and clinically important fluid overload requiring temporary dialysis support.
02
Neurological injury
Microangiopathy, hypertension and metabolic disturbance can cause irritability, seizures, encephalopathy, stroke or severe cerebral oedema in children.
03
Pancreatic involvement
Microvascular injury can produce abdominal pain, acute pancreatitis, hyperglycaemia and occasionally ongoing insulin-dependent diabetes mellitus after recovery.
04
Cardiac involvement
Hypertension, fluid overload, ischaemia and electrolyte disturbance can cause heart failure, dangerous arrhythmia or myocardial dysfunction.
05
Chronic renal sequelae
Persistent proteinuria, hypertension, hyperfiltration injury or reduced eGFR may emerge after an apparently complete initial haematological recovery.
Monitoring and follow-up
Record urine output at least hourly in unstable or oliguric children and weigh at least twice daily during evolving HUS.
Repeat FBC, platelets, film and LDH to establish whether microangiopathic haemolysis is accelerating or resolving.
Trend potassium, bicarbonate, creatinine, glucose, calcium and phosphate at a frequency determined by renal instability.
Measure blood pressure frequently with an appropriate cuff and repeat neurological observations after every significant change.
Assess respiratory effort, saturation and signs of fluid overload after transfusion or any fluid prescription change.
After discharge, monitor blood pressure, urinalysis, proteinuria and eGFR because renal sequelae can follow apparent recovery.
Follow public-health clearance and exclusion advice for the child and relevant high-risk contacts.
Special situations
The triad evolves
A child may have normal platelets early, so serial blood counts are essential after high-risk bloody diarrhoea.
Diarrhoea may be improving
HUS often becomes apparent as gastrointestinal symptoms recede, making new pallor or oliguria especially important.
Low platelets rarely need platelets
Treat the child and bleeding risk, not the count alone, because transfused platelets may enter ongoing microthrombi.
Fluid strategy changes quickly
Early dehydration may justify replacement, but established oliguria turns the same volume into hypertension and pulmonary oedema.
STEC status has public-health consequences
Specific specimen labelling, clinical notification and contact advice help prevent nursery, household and foodborne spread.
Common pitfalls
01
Do not wait for simultaneous anaemia, thrombocytopenia and AKI before escalating a compatible evolving illness.
02
Do not omit a stool or rectal specimen because diarrhoea has stopped.
03
Do not prescribe antibiotics or loperamide routinely for suspected STEC bloody diarrhoea.
04
Do not give full maintenance fluid automatically after oliguria develops.
05
Do not transfuse platelets for the number alone without bleeding, procedure or specialist indication.
06
Do not assume all diarrhoea-associated HUS is harmless after dialysis ends.
07
Do not miss neurological change by attributing irritability only to hospital distress.
08
Do not forget clinical notification to the health protection team.
Do not transfuse platelets solely for a low count; reserve them for clinically important bleeding or an invasive procedure after specialist discussion because platelet consumption is ongoing.
Transfuse red cells for clinically significant or symptomatic anaemia using the paediatric transfusion plan, with close attention to potassium and fluid volume.
Dialysis is used for refractory hyperkalaemia, acidosis, pulmonary oedema, uraemic complications or uncontrolled fluid overload; the decision is not based on urea or creatinine alone.
Notify suspected HUS to the local health protection team on clinical suspicion, apply enteric infection control, and obtain exposure history including farms, animals, food, water, nursery and household cases.
indicates central nervous system involvement and requires intensive monitoring.
Potassium elevation, severe acidosis, pulmonary oedema, uraemic symptoms or anuria requires immediate nephrology and critical-care assessment for kidney replacement therapy.
HUS without preceding diarrhoea, recurrent episodes, family history, very early onset or persistent complement abnormality raises concern for complement-mediated atypical HUS.
Fever with neurological signs, profound coagulopathy or shock requires simultaneous assessment for sepsis, meningitis and disseminated intravascular coagulation.
Why
Distinguish complement-mediated atypical HUS, TTP and other microangiopathies when presentation is atypical.
Interpretation and limitations
Specialists guide sampling before plasma or complement therapy where possible; treatment must not await every result in life-threatening disease.
3Use supportive transfusion, fluid and kidney-replacement decisions based on physiology rather than waiting for diagnostic completeness.
03FluidAdapt to the renal phaseDiarrhoea, dehydration and falling filtration coexist.+
1Correct genuine early hypovolaemia with carefully reassessed isotonic fluid before significant oliguria when indicated.
2Once oliguric, prescribe input from measured losses and insensible need, avoiding automatic full maintenance and potassium-containing fluid.
3EscalationUse dialysis rather than repeated fluid or diuretic escalation for refractory overload, pulmonary oedema, hyperkalaemia, acidosis or uraemia.
04AtypicalInvestigate complement-mediated diseaseSTEC is unsupported, disease recurs or the course is unusually severe or persistent.+
1Send complement, ADAMTS13 and genetic or antibody investigations through the specialist thrombotic-microangiopathy pathway.
2Exclude pneumococcal, autoimmune, transplant, medicine and malignant-hypertension causes.
3Start specialist complement inhibition promptly when complement-mediated aHUS is sufficiently suspected, with required meningococcal prevention and infection counselling.