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🧬 Haemolytic Uraemic Syndrome (HUS)

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Urology

⚠️ Important: HUS is often triggered by E. coli 0157:H7 producing Shiga toxin. Antibiotics 🚫 and antimotility drugs 🚫 should be avoided as they worsen outcomes. Mortality is highest in the elderly, due to intravascular haemolysis 🩸, thrombocytopenia 🩸, and acute kidney injury (AKI) ⚡. Severe cases may require plasma exchange 🔄 or haemofiltration 💧.

📖 Overview

HUS = triad of microangiopathic haemolytic anaemia (MAHA) 🩸, thrombocytopenia 🩸, and acute kidney injury (AKI) ⚡.
RBC fragmentation → anaemia; platelet consumption → bleeding risk; renal microthrombi → AKI.

🧬 Aetiology

Most common in children (after diarrhoea 💩) or elderly (with AKI).
Verocytotoxin-producing E. coli (VTEC), esp. strain 0157:H7 🦠.
Adults: may follow drug exposure (e.g. ciclosporin, quinine).
Familial HUS: deficiency of Factor H (a complement regulator) ➡️ uncontrolled complement activation.

⚙️ Pathophysiology

Shiga toxin damages endothelium → renal microvascular thrombosis 🧱.
Platelet activation + aggregation → thrombocytopenia 🩸.
Shear stress in narrowed vessels → RBC fragmentation ✂️ (schistocytes).

📊 Classification: Diarrhoea vs No Diarrhoea

D+ HUS (95%): Diarrhoea-associated, typically post-E. coli infection in children 👧. ADAMTS13 levels usually normal.
D- HUS (5%): Atypical form (aHUS) due to complement dysregulation 🌀. Affects all ages; often recurrent and more severe.

Haemolytic Uremic Syndrome (HUS) is characterised by the triad of microangiopathic haemolytic anaemia, thrombocytopenia, and acute kidney injury (AKI). It can be classified into typical (D+), atypical (D−), and secondary forms.

Type of HUS	Trigger / Cause	Key Clinical Features	Investigations	Management
Typical HUS (D+)	Post-diarrhoeal illness, usually bloody diarrhoea Most commonly E. coli O157:H7 (Shiga toxin–producing) Also Shigella dysenteriae	Mainly affects children <5 years Preceding gastroenteritis Haemolytic anaemia, thrombocytopenia, AKI	FBC: schistocytes, low Hb, thrombocytopenia Raised urea, creatinine Stool PCR / culture for Shiga toxin	Supportive: fluids, dialysis if needed Avoid antibiotics & antimotility drugs (↑ toxin release) Most children recover fully
Atypical HUS (D−)	Complement pathway dysregulation (genetic mutations, autoantibodies) No diarrhoeal prodrome	Any age (children & adults) Recurrent, chronic course Progressive renal dysfunction	Complement levels (low C3, normal C4) Genetic testing (e.g. factor H, I, MCP) Exclude STEC infection	Supportive (dialysis, BP control) Eculizumab (anti-C5 monoclonal Ab) Plasma exchange in some cases
Secondary HUS	Secondary to another condition: Pregnancy (esp. postpartum) Drugs (e.g. ciclosporin, tacrolimus, chemotherapy) Autoimmune disease (SLE, antiphospholipid syndrome) Malignancy, bone marrow transplant	Variable age History of underlying trigger Similar triad: MAHA, thrombocytopenia, AKI	Exclude STEC & complement defects Investigate underlying condition (autoantibodies, pregnancy screen, drug history)	Treat underlying cause Supportive care Eculizumab may help in some complement-mediated secondary cases

⚠️ UK Clinical Pearls

🧪 Notifiable disease: STEC/E. coli O157 must be reported to public health.
👶 Children: HUS is the leading cause of AKI in children in the UK – urgent paediatric nephrology input required.
💉 Transfusions: Red cells often needed; avoid platelet transfusion unless life-threatening bleeding.
📊 Monitoring: Daily U&E, FBC, BP, and strict fluid balance are essential.
🌱 Prognosis: Mortality <5% in children with D+ HUS; poorer in atypical/secondary forms (risk of ESRD).

🧾 Causes of Atypical HUS (D-)

💊 Medications: Mitomycin C, Ticlopidine, Cyclosporine, Tacrolimus, Quinine
Combination chemotherapy 💉
Radiotherapy ☢️ or congenital causes 🧬
Malignancy: prostate, gastric, pancreatic cancers 🎗️
Connective tissue disease: scleroderma, antiphospholipid syndrome 🤲

🔍 Differential Diagnosis

DIC vs HUS: DIC shows abnormal coagulation (↑ PT/APTT, ↓ fibrinogen). HUS → coagulation profile remains normal ✅.

⚡ Clinical Features

Prodrome: gastroenteritis with bloody diarrhoea 💩.
Signs: jaundice 🟡, pallor 😓, bruising/petechiae 🔴.
Red/brown urine ⚫, rash, hypertension 📈, uraemia 🧪.
Mostly children, but also seen in adults (esp. aHUS).

🔬 Investigations

FBC: Anaemia (Hb < 8 g/dL), thrombocytopenia 📉.
Blood film: Schistocytes ✂️, polychromasia.
Biochemistry: ↑ LDH, ↑ unconjugated bilirubin, ↓ haptoglobin.
Coagulation profile: PT/APTT/fibrinogen normal (distinguishes from DIC ✅).
Stool culture: Look for E. coli 0157:H7 🦠.
Kidney biopsy: Consider if diagnosis uncertain or severe disease 🧾.
ADAMTS13: Typically normal in HUS (reduced in TTP).

🩺 Management

Immediate care: Specialist unit transfer 🚑. Avoid antibiotics 🚫, antimotility drugs 🚫, and routine platelet transfusions 🚫.
Renal support: Dialysis required in ~50% of AKI cases 💧. Up to 85% recover renal function in D+ HUS ✅.
Plasma exchange: Daily plasmapheresis with FFP is treatment of choice in severe/atypical HUS 🔄.
Adjuncts: If refractory, consider agents like eculizumab 💉 (complement inhibitor, esp. for aHUS). Steroids are not effective 🚫.
Supportive: Manage hypertension 💊, anaemia (transfusion if necessary), fluids ⚖️.
Prognosis: Most children recover 🌱, but atypical HUS has poorer outcomes and high recurrence risk ⚠️.

📚 References

PLEASE NOTE LEGAL ADVICE: The contents are under continuing development and improvements and may contain errors of omission or fact. Feedback vital and always welcome at drokane at gmail.com. This is not to be used for the assessment, diagnosis or management of patients. It should not be regarded as medical advice. It is only for educational purposes. Please adhere to your local protocols. If you are unwell please seek healthcare advice from your doctor. This does not replace senior or specialist advice. If you do not accept this then please do not use the website. If you need medical advice, please consult a doctor or other appropriate medical professional. If you are a medical professional and you need advice then speak to your senior or colleagues.

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