Haemolytic Uraemic Syndrome

Question 1

Define

Answer 1

Characterised by Microangiopathic haemolytic anaemia (MAHA)

→Intravascular haemolysis and red cell fragmentation

Endothelial damage triggers:
•Thrombosis •Platelet consumption •Fibrin strand deposition Mainly in renal vasculature

The strands cause mechanical destruction of passing RBCs Thrombocytopaenia and AKI result

DEFINITION: triad of:

1. Microangiopathic haemolytic anaemia (MAHA)
2. Acute renal failure
3. Thrombocytopaenia

There are TWO forms of HUS:

• D+ = diarrhoea-associated form
• D- = no prodromal illness identified

Question 2

Causes

Answer 2

• Endothelial injury results in platelet aggregation and the release of unusually large vWF multimers and activation of platelets and the clotting cascade
• This leads to small vessel thrombosis
• The glomerular-afferent arteriole and capillaries are particularly vulnerable - they undergo fibrinoid necrosis
• This leads to renal ischaemia and acute renal failure
• The thrombi also promote intravascular haemolysis

Causes:

• 90% from E. coli strain O157

Produces a verotoxin/Shiga toxin that attacks endothelial cells

Drugs

• COCP
• Ciclosporin
• Mitomicin
• 5-fluorouracil

Others:

• Malignant hypertension
• Malignancy
• Pregnancy
• SLE
• Scleroderma

Question 3

Epidemiology

Answer 3

typically affects young children in outbreaks

(more common the sporadically) after eating uncooked meat

Question 4

Risk factors

Answer 4

Rural populations, warmer summer months, young age, contact with farm animals, older pts

Question 5

Symptoms

Answer 5

• Abdominal pain (sever colic)
• Watery diarrhoea that turns bloody 1-3 days later
• Malaise, fever, nausea, fatigue
• Renal: oliguria or anuria, haematuria

Question 6

Signs

Answer 6

General → pallor from anaemia, slight jaundice form haemolysis Generalised oedema, hypertension and retinopathy
GI → abdominal tenderness
AKI → haematuria, proteinuria

Question 7

Investigations

Answer 7

FBC

• Normocytic anaemia
• High neutrophils
• Very low platelets

U&Es

• High urea
• High creatinine
• High K+
• Low Na+

Clotting

• Normal APTT and fibrinogen levels (abnormality may indicate DIC)
• LFTs
• High unconjugated bilirubin
• High LDH from haemolysis

Blood cultures

• ABG
• Low pH
• Low bicarbonate
• Low PaCO2
• Normal anion gap

Blood Film

• Schistocytes
• High reticulocytes and spherocytes

Urine

• 1+ g protein/24 hrs
• Haematuria

Stool Samples

• MC&S
• Renal Biopsy
• Can distinguish between D+ and D- HUS