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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Caused by severe ADAMTS13 deficiency (<10%) — autoimmune (antibodies against ADAMTS13) or congenital. Ultra-large VWF multimers aggregate platelets in microvasculature
- Classic pentad: thrombocytopenia, microangiopathic haemolytic anaemia (MAHA), neurological signs, renal impairment, fever — full pentad present in <10%, do NOT wait for all features
- Blood film: SCHISTOCYTES (fragmented red cells) = MAHA. NORMAL coagulation screen (unlike DIC)
- HAEMATOLOGICAL EMERGENCY: untreated mortality >90%. Treatment: plasma exchange (PEX) within hours + steroids + caplacizumab
- NEVER give platelet transfusions in TTP — can worsen microvascular thrombosis ("fuel on the fire")
Overview
Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy (TMA) caused by severe deficiency of the von Willebrand factor-cleaving protease ADAMTS13 (<10% activity). Without ADAMTS13, ultra-large VWF multimers accumulate and cause spontaneous platelet aggregation in the microvasculature, leading to microvascular thrombosis, consumption thrombocytopenia, and mechanical haemolysis (MAHA). The majority of cases are acquired autoimmune (anti-ADAMTS13 antibodies); congenital TTP (Upshaw-Schulman syndrome) is very rare.
Epidemiology
TTP is rare, with an incidence of approximately 3-6 per million per year. It predominantly affects adults (peak age 30-50 years) and is more common in women (3:1) and in Black populations. Triggers include infections, pregnancy, drugs (quinine, ticlopidine), autoimmune disease (SLE), and post-transplant. Without treatment, mortality exceeds 90%; with plasma exchange, survival is >80%.
Clinical Features
Symptoms
Fatigue, pallor, jaundice (MAHA + thrombocytopenia)
Confusion, headache, seizures, focal neurological deficits (cerebral microvascular thrombosis)
Petechiae and purpura (thrombocytopenia)
Abdominal pain, nausea, diarrhoea
Dark urine (haemoglobinuria from intravascular haemolysis)
Fever (present in ~30%)
Signs
Fluctuating neurological signs — confusion, dysarthria, visual disturbance, coma
Petechiae, purpura, bruising
Jaundice
Pallor
Fever
Investigations
First-line
FBCThrombocytopenia (often <30 × 10⁹/L) + anaemia (haemolysis)
Blood filmSCHISTOCYTES (fragmented red cells) — ESSENTIAL finding. Polychromasia (reticulocytosis). Must request URGENT blood film in suspected TTP
Coagulation screen (PT, APTT, fibrinogen)NORMAL — this distinguishes TTP from DIC (where PT/APTT are prolonged and fibrinogen is low)
LDH, haptoglobin, reticulocytes, bilirubinRaised LDH (markedly — often >1000), low haptoglobin, raised reticulocytes, raised unconjugated bilirubin — confirms MAHA
Second-line
ADAMTS13 activity<10% = TTP (send BEFORE starting plasma exchange but do NOT delay treatment while awaiting result). ADAMTS13 inhibitor level to confirm autoimmune aetiology
DAT (Coombs)NEGATIVE — haemolysis is mechanical (schistocytes), not autoimmune
U&Es, creatinineMild renal impairment common; severe AKI suggests HUS rather than TTP
Specialist
PLASMIC scoreClinical prediction score for ADAMTS13 deficiency: platelets <30, haemolysis markers, no active cancer, no SCT, MCV <90, INR <1.5, creatinine <176 µmol/L. High score predicts ADAMTS13 <10%
Management
BSH Guidelines on TTP (2023)1
Emergency — do NOT delay
- TTP is a HAEMATOLOGICAL EMERGENCY — start treatment on clinical suspicion (do not wait for ADAMTS13 result)
- Plasma exchange (PEX): daily until platelet count normalises (>150 × 10⁹/L for ≥2 days). Removes autoantibodies and ultra-large VWF, replaces ADAMTS13
- If PEX unavailable immediately: give FFP infusion as a bridge
2
Immunosuppression
- Corticosteroids: methylprednisolone 1 g IV daily for 3 days, then oral prednisolone 1 mg/kg
- Rituximab (anti-CD20): now given early in acute TTP to reduce relapse. Reduces autoantibody production
3
Caplacizumab
- Anti-VWF nanobody — prevents VWF-platelet interaction
- Accelerates platelet recovery, reduces organ damage and mortality
- Continue for 30 days after last PEX — reduces relapse rate significantly
4
Critical: do NOT give platelet transfusions
- Platelet transfusion in TTP is DANGEROUS — provides substrate for further microvascular thrombosis ("fuel on the fire")
- Only exception: life-threatening haemorrhage (extremely rare scenario)
Complications
- Stroke: Cerebral microvascular thrombosis — the major cause of acute mortality
- Myocardial ischaemia: Cardiac microvascular thrombosis — troponin often elevated
- Relapse: Occurs in ~30-50% of autoimmune TTP — ADAMTS13 monitoring guides management
- Chronic cognitive impairment: Subclinical brain injury even in treated patients
UKMLA Exam Tips
- 1Schistocytes + thrombocytopenia + NORMAL coagulation = TTP (or HUS). If coagulation abnormal = DIC
- 2NEVER give platelet transfusions in TTP — classic exam warning. It worsens microvascular thrombosis
- 3Plasma exchange is the definitive treatment — reduces mortality from >90% to <20%
- 4Do NOT wait for ADAMTS13 result before starting PEX — treat on clinical suspicion
- 5TTP vs HUS: TTP = neuro features predominate, mild renal. HUS = severe AKI predominates, less neuro (especially in children post-diarrhoeal HUS from Shiga toxin/E. coli O157)
- 6ADAMTS13 <10% = TTP. Normal ADAMTS13 with MAHA + thrombocytopenia = consider other TMAs (complement-mediated, drug-induced)
practicetest your knowledge on ttpApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — haematology and beyond.
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