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ITP vs TTP vs HUS for MRCP Part 1

TL;DR

Platelet Disorders: ITP vs. TTP vs. HUS MRCP Part 1 is a core exam topic requiring rapid differentiation between isolated thrombocytopenia and thrombotic microangiopathies. ITP presents with isolated platelet destruction, while TTP and HUS involve haemolysis and organ dysfunction. Recognising neurological features (TTP), renal failure (HUS), and isolated thrombocytopenia (ITP) is key to scoring marks quickly.


Why this matters

Platelet disorders are a frequent testing domain in MRCP Part 1, often appearing as short clinical vignettes where rapid pattern recognition is essential. The exam expects you to distinguish between immune-mediated thrombocytopenia (ITP) and thrombotic microangiopathies (TTP/HUS) with confidence.

Errors in differentiation are common and costly—not just in exams but in clinical practice. Missing TTP, for example, delays life-saving plasma exchange.

For a structured overview of the exam, see the MRCP Part 1 overview.


Core sections

1. The Big Picture: Key Differences

All three conditions involve thrombocytopenia, but the mechanism and urgency differ:

  • ITP → autoimmune platelet destruction (benign but symptomatic)

  • TTP/HUS → thrombotic microangiopathy (life-threatening)

2. High-yield comparison table

Feature

ITP

TTP

HUS

Mechanism

Autoimmune platelet destruction

ADAMTS13 deficiency → vWF aggregation

Endothelial damage (Shiga toxin)

Platelets

↓↓↓

↓↓↓

↓↓↓

Hb

Normal

↓ (haemolysis)

↓ (haemolysis)

Blood film

Normal

Schistocytes

Schistocytes

Neurology

No

Prominent

Rare

Renal

No

Mild

Severe

Fever

No

Often

Sometimes

Treatment

Steroids

Plasma exchange

Supportive

3. The 5 most tested subtopics

(1) Pathophysiology

  • ITP: IgG antibodies target platelets → splenic destruction

  • TTP: ADAMTS13 deficiency → accumulation of ultra-large vWF multimers

  • HUS: Endothelial injury, typically from E. coli O157:H7 toxin

(2) Clinical presentation

  • ITP:

    • Petechiae, purpura

    • No systemic illness

  • TTP:

    • Neurological symptoms (confusion, seizures)

    • Fever + thrombocytopenia + haemolysis

  • HUS:

    • Preceded by diarrhoeal illness

    • Acute kidney injury

(3) Laboratory features

  • ITP: isolated thrombocytopenia

  • TTP/HUS:

    • Schistocytes

    • ↑ LDH

    • ↑ indirect bilirubin

    • Negative Coombs test

(4) Management priorities

  • ITP:

    • First-line: corticosteroids

    • IVIG if severe

  • TTP:

    • Plasma exchange (urgent)

    • Steroids ± rituximab

  • HUS:

    • Supportive care

    • Dialysis if needed

(5) Exam trigger phrases

  • “Isolated thrombocytopenia” → ITP

  • “Confusion + haemolysis” → TTP

  • “Child + diarrhoea + renal failure” → HUS

4. 10 High-yield points for MRCP Part 1

  1. TTP is a medical emergency

  2. Plasma exchange is first-line in TTP

  3. ADAMTS13 deficiency defines TTP

  4. HUS follows Shiga toxin-producing E. coli

  5. Schistocytes indicate microangiopathic haemolysis

  6. ITP has normal clotting studies

  7. Neurological features → think TTP

  8. Renal failure → think HUS

  9. Platelet transfusion is avoided in TTP

  10. Coombs test is negative in TTP/HUS


Practical examples / mini-cases

Case

A 28-year-old woman presents with confusion, fever, and bruising. Blood tests show Hb 7.9 g/dL, platelets 18 ×10⁹/L, raised LDH, and schistocytes.

What is the most appropriate immediate management?

A) Platelet transfusionB) IV antibioticsC) Plasma exchangeD) Oral steroids

Answer: C) Plasma exchange

Explanation: This is classic TTP—thrombocytopenia, haemolysis, and neurological symptoms. Plasma exchange is life-saving and should not be delayed.


Common pitfalls (5 bullets)

  • Confusing ITP with TTP due to thrombocytopenia alone

  • Missing schistocytes on blood film

  • Giving platelet transfusions in TTP

  • Ignoring neurological symptoms

  • Prescribing antibiotics in HUS


Practical study-tip checklist

Medical student preparing for MRCP Part 1 studying platelet disorders and thrombocytopenia

FAQs

1. How do you differentiate TTP from HUS?

TTP presents with prominent neurological features, while HUS is characterised by severe renal failure, often following diarrhoea.

2. Is platelet transfusion safe in TTP?

No. It may worsen thrombosis and is avoided unless there is life-threatening bleeding.

3. What is the first-line treatment for ITP?

Oral corticosteroids are first-line, with IVIG used in severe cases.

4. Why avoid antibiotics in HUS?

They may increase toxin release from E. coli, worsening endothelial injury.

5. What is the key diagnostic clue for TTP?

Thrombocytopenia with haemolysis and neurological symptoms is highly suggestive.


Ready to start?

Platelet disorders are high-yield and frequently tested. Strengthen your preparation with the MRCP Part 1 overview and sharpen your exam skills using Free MRCP MCQs today.


Sources

 
 
 

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