Microangiophathic haemolytic anaemia (MAHA) & Thrombotic thrombcytopenic purpura (TTP) (BSH 2012)


Incidence of acute idiopathic TTP:  6 per million per year in UK

Untreated mortality:                         >90%


TTP Pathophysiology


Congenital deficiency of ADAMTS13, or acquired autoantibodies against ADAMTS13


ADAMTS13 – a metalloproteinase responsible for cleaving ultra large VWF multimers (ULVWF)


In the absence of ADAMTS13, ULWVF causes spontaneous platelet aggregation under conditions of high shear stress, e.g. microvasculature, brain, heart, kidneys.

Thrombocytopenia results from consumption within platelet-rich thrombi

Anaemia results from mechanical fragmentation of red cells through partly occluded vessels.


TTP Clinical Features


Classic Pentad – Fever, Thrombocytopenia, Renal Failure, Fluctuating neurology & MAHA



33% No Neurological Signs

Fever and renal impairment may not be prominent




FBC                             – median plt count 10-30 & Hb 80-100 at diagnosis

Film                             – thrombocytopenia, schistocytes

Haemolysis markers – haptoglobins, Retic, LDH, Normal DAT

Coag screen               – normal

Trop T                        – raised in 50%, poor prognostic sign


ADAMTS13 Assays

  • <5% +/- presence of an inhibitor confirms the diagnosis

  • TTP vs HUS – A level of <5% has 90% specificity for TTP

  • Activity, Antigen and Autoantibody assays available.

  • Activity assays based on the failure of patient plasma to degrade VWF multimers


Other Ix of MAHA/TMA


Pregnancy Test

Infection         – HIV, Hep B, Hep C

AI                    – TFT, Autoantibody screen

Cardiac           – ECG, Echo

Neuro             – CT/MRI Brain

Malignancy    – CT CAP, tumour markers


Differential Diagnosis of MAHA/TMA


Acquired TTP

Congenital TTP

  • 100 patients worldwide. Presents at any age. Often asymptomatic until a precipitating event sends a chronically low ADAMTS13 even lower.


  • HELLP, Eclampsia, AFLP

  • Diagnostically difficult. Pregnancy may be precipitant for 5-25% of TTP cases

Haemolytic Uraemic Syndrome (HUS)

  • E. coli shiga toxins

Atypical HUS (aHUS)

  • Excess activation of alternate complement pathway

  • May be genetic, acquired autoantibody or idiopathic


  • 15% of MAHA cases

  • TTP - Quinine, tacrolimus, simvastatin, interferon, OCP, trimethoprim

  • HUS – Gemcitabine, bleomycin, mitomycin-C

Malignant Hypertension


  • Adenocarcinoma especially. Early or late stage disease. ADAMTS13 not low.


  • Lack of ADAMTS13 deficiency, poor response to PLEX. Anecdotal use of defibrotide


  • CMV, Adenovirus, Herpes Simplex, Hep B, Hep C, Meningococcus, Fungal

  • HIV – may be presenting feature. ADAMTS13 <5% associated with a relatively higher CD4 count


  • Lupus nephritis, Scleroderma, Evans Syndrome, Vasculitis

Catastrophic Antiphospholipid Syndrome (CAPS)


Treatment of Acute TTP


1. Start Plasma Exchange (PLEX) within 4 hours of diagnosis

Removes antibody and ULMW VWF Multimers

Replaces ADAMTS13

  • 1.5x plasma volume exchange daily for 3 days, then re-assess

  • Continue PLEX until plt count >150 (Complete remission) & for 2 more days beyond

  • Use SD-FFP to reduce risk of TTI & adverse immune responses.

  • (Note: MB-FFP associated with longer hospital stay and greater number of exchanges)

  • (Rock et al NEJM 1991 for PLEX vs Plasma transfusion survival)


2. Start steroids

Stop production of antibody

  • 1g IV Methylprednisolone or 1mg/kg PO Prednisolone

  • Dose and length of treatment varies between centres

  • Expect an exacerbation of symptoms+thrombocytopenia 7-10 days after steroids

3. Rituximab (Off license)

Stop production of antibody

  • Dosed every 3-4 days

  • Reduces No. of PLEX, length of stay and time to CR

  • Median 10 days to effect —> better outcomes if given early

  • Some centres give to all patients, some only to those with cardiac/neuro complications

4. Caplacizumab - see below

5. Supportive Care


Folic Acid

LMWH + Aspirin once plt count >50 (SD-FFP deficient in protein S)

Red cell transfusion if required

Consider Hep B vaccination



  • 28kD bivalent camelid Nanobody, targeting A1 region of VWF

  • (Camelid’s produce heavy-chain only antibodies which are stable and fully functional)

  • Theory: release platelets from their ULVWF-bound state, returning them to the circulation


  • First dose should be given IV pre-plasma exchange (but do not delay PLEX for this)

  • 10mg SC after 1st exchange then 10mg daily SC for 30 days

  • If ADAMTS13 <10% at day 30 —> continue to 60 days

TITAN Study NEJM 2016, Phase II

  • 30 days capla for TTP diagnosed based on clinical basis (ie pre-ADAMTS13 level result)

  • Could not recruit, stopped early, ?Poor study design (Drug have to be given before PLEX)

  • Despite this, did show reduced time to platelet recovery, reduced exacerbation, but higher relapse

  • Conclusion: Bridging therapy that reduces microthrombi but does not treat the underlying disease



  • Randomised, double-blind, placebo-controlled, multi-national study

  • Plasma exchange allowed prior to starting drug

  • Able to extend drug beyond 30 days if ADAMTS13 level still low, or if exacerbation occurs.

  • Reduces No. of exchanges, volume of plasma, No. of ICU days, No. of days in hospital

  • SE: More bleeding, but minor sites and severity (nose, gums) – theory: organs don’t bleed as full of microthrombi, skin and epithelium has the space to bleed. Aim to manage symptoms, but do not stop caplacizumab.


Treatment of Specific Scenarios


Congenital TTP

  • Consider long-term prophylaxis – SD-FFP transfusion every 10-20 days

  • Supplement during pregnancy

  • Alternative: ‘8Y’  - a intermediate purity FVIII concentrate containing ADAMTS13



  • Defined as an episode of acute TTP occurring >30 days after remission

  • Occurs in 20-50% of cases

  • Can be averted by ADAMTS13 monitoring and pre-emptive rituximab


Other therapies

  • 1st or 2nd line: Rituximab 375mg/m2 weekly for 4 doses

  • 2nd line: Ciclosporin, splenectomy


Further Details of Plasma Exchange


£3,000 per exchange (including cost of SD-FFP)

Two methods of separation - Centrifugal or Filtration

Removes ultra large vWF, replaces ADAMTS13 and removes inhibitor (e.g. antibody)

FFP contains around 1 unit ADAMTS13 per 1ml/kg. So 15ml/kg --> Raise ADAMTS13 by up to 15% (however rapidly consumed or deactivated by antibody)

Replace 1-1.5x plasma volume & takes 110-150 minutes per exchange

Flow rate around 120ml/min through machine

Centrifuge at 2400 rpm

ACD-A anticoagulant

Perform daily until platelet count >150 on 3 consecutive days, then wean off.



lab notes on adamts13 assays

ADAMTS13 Indirect Activity ELISA

Technozym is one supplier. Takes 4-6 hours.

A microtitre plate is coated with anti-GST, subsequently bound to VWF73.

A source of ADAMTS-13 is then added (Calibrator, Control or Patient).

Cleavage of the substrate allows HRP antibody to bind to the remaining fragment --> colour change



ADAMTS-13 Inhibitor ELISA


To distinguish acquired from congenital TTP

Technozym is one supplier

A microtire plate is coated with recombinant ADAMTS-13.

When incubated with a source of ADAMTS-13 inhibitor (Claibrator, Control, Patient), the antibody will bind to ADAMTS-13.

Addition of an HRP antibody will produce a colour change

(Simple alternative: 50:50 mix with normal plasma)

adamst 2.png


Other ADAMTS-13 Assays



  • may be normal in TTP, uninformative without activity assay


Direct Activity

  • SDS Gel Electrophoresis – incubate vWF with plasma and measure the drop in multimer size compared to diluted normal plasmas. Complicated and time consuming.

  • SDS PAGE & Western blotting – similar to above

  • FRET Assays – fluorescent resonance energy transfer


Anti-ADAMTS13 Autoantibodies

  • 50/50 mix with normal plasma