Thrombotic microangiopathies: TTP vs HUS
- Lesion
Platelet clots plug small vessels, cut red cells and starve organs. In TTP the brain suffers most; in HUS the kidney.
What it is
Thrombotic microangiopathies combine microangiopathic haemolytic anaemia, thrombocytopenia and organ injury from platelet-rich thrombi in small vessels. In TTP, deficiency of ADAMTS13, the protease that cleaves very large von Willebrand factor multimers, lets those multimers aggregate platelets; it is usually acquired through an autoantibody and rarely inherited. In HUS, endothelial injury, usually from Shiga toxin of E. coli O157:H7 in children, or uncontrolled complement activation in atypical HUS, damages renal microvessels. Unlike DIC, the coagulation cascade is not primarily activated, so PT and PTT are usually normal.
Structure
- Hyaline platelet-rich thrombi in arterioles and capillaries of brain, heart, kidney and other organs.
- Kidney: glomerular capillary thrombi, endothelial swelling, cortical necrosis in severe HUS.
- Smear: schistocytes and low platelets.
Step by step
- TTP: ADAMTS13 is absent or inhibited, so ultralarge vWF multimers accumulate.
- TTP: the multimers bind and activate platelets in high-shear microvessels.
- HUS: Shiga toxin enters endothelial cells and blocks protein synthesis, or complement attacks unprotected endothelium.
- Platelet thrombi occlude microvessels; platelets are consumed.
- Red cells are sheared into schistocytes; organs become ischaemic (brain, kidney).
TTP vs HUS vs DIC
| Feature | Cause | Organ most hit | PT and PTT | Treatment principle |
|---|---|---|---|---|
| TTP | ADAMTS13 deficiency, usually an autoantibody | Brain (also kidney, heart) | Normal | Plasma exchange, immunosuppression |
| Typical HUS | Shiga toxin-producing E. coli (O157:H7) in children | Kidney | Normal | Supportive, dialysis |
| Atypical HUS | Defects in complement regulators | Kidney | Normal | C5 inhibition |
| DIC | Systemic activation of coagulation (sepsis, obstetric, cancer) | Many organs, bleeding | Prolonged | Treat the cause |
Clinical notes
- Any patient with thrombocytopenia, schistocytes and confusion needs urgent evaluation for TTP, which is fatal without plasma exchange.
- Platelet transfusion may worsen thrombosis in TTP.
Test yourself
Think of the answer, then tap the question to see it.
Which enzyme is deficient in TTP and what does it normally do?
ADAMTS13, which cleaves very large von Willebrand factor multimers.
What causes typical HUS in children?
Shiga toxin from E. coli O157:H7 after bloody diarrhoea, injuring renal endothelium.
How do coagulation tests separate TTP from DIC?
PT and PTT are usually normal in TTP and HUS but prolonged in DIC.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Thrombotic thrombocytopenic purpura: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Hemolytic-uremic syndrome: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Atypical hemolytic-uremic syndrome: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.