[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Red cells and bleeding disorders](https://durgical.com/en/general-pathology/areas/red-cells/) › Thrombotic microangiopathies: TTP vs HUS

# 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.

Updated Nov 12, 2026

## Key points

- Classic TTP pentad: fever, thrombocytopenia, microangiopathic haemolysis, neurologic signs, renal failure; most patients do not have all five.
- TTP: ADAMTS13 deficiency (autoantibody); plasma exchange removes antibody and supplies enzyme.
- Typical HUS: children after bloody diarrhoea from Shiga toxin-producing E. coli; acute kidney injury dominates.
- Atypical HUS: inherited or acquired defects of complement regulators (factor H, factor I, CD46, C3, factor B); C5 inhibitors work.
- Normal PT and PTT separate TMA from DIC.

## 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](https://durgical.com/en/conditions/thrombotic-thrombocytopenic-purpura/) | ADAMTS13 deficiency, usually an autoantibody | Brain (also kidney, heart) | Normal | Plasma exchange, immunosuppression |
| [Typical HUS](https://durgical.com/en/conditions/hemolytic-uremic-syndrome/) | Shiga toxin-producing E. coli (O157:H7) in children | Kidney | Normal | Supportive, dialysis |
| [Atypical HUS](https://durgical.com/en/conditions/hemolytic-uremic-syndrome/) | Defects in complement regulators | Kidney | Normal | C5 inhibition |
| [DIC](https://durgical.com/en/conditions/disseminated-intravascular-coagulation/) | 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.

## Memory aid

TTP: the protease is missing and the brain pays. HUS: the toxin or complement hits, and the kidney pays.

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/thrombotic-microangiopathies-ttp-vs-hus/)

[More Pathology questions →](https://durgical.com/en/practice/?f=pathology)

## Elsewhere in DurgiPedia

- [Complement: three pathways, MAC, regulators](https://durgical.com/en/immunology/complement-three-pathways-mac-regulators/)
- [Primary hemostasis and platelets](https://durgical.com/en/physiology/primary-hemostasis-and-platelets/)

## Connections

## Related 4

- [Thrombosis and Virchow's triad](https://durgical.com/en/general-pathology/thrombosis-and-virchow-s-triad/)
- [Disseminated intravascular coagulation: how consumption causes both clots and bleeding](https://durgical.com/en/general-pathology/disseminated-intravascular-coagulation-how-consumption-causes-both-clots-and-ble/)
- [Traumatic haemolysis](https://durgical.com/en/general-pathology/traumatic-haemolysis/)
- [Toxin-mediated diarrhoea: cholera and E. coli](https://durgical.com/en/general-pathology/toxin-mediated-diarrhoea-cholera-and-e-coli/)

## Related conditions 5

- [Thrombotic thrombocytopenic purpura](https://durgical.com/en/conditions/thrombotic-thrombocytopenic-purpura/)
- [Hemolytic uremic syndrome (HUS)](https://durgical.com/en/conditions/hemolytic-uremic-syndrome/)
- [Acute kidney injury](https://durgical.com/en/conditions/acute-kidney-injury/)
- [Disseminated intravascular coagulation](https://durgical.com/en/conditions/disseminated-intravascular-coagulation/)
- [Hypertensive emergency and urgency](https://durgical.com/en/conditions/hypertensive-emergency-and-urgency/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

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](https://medlineplus.gov/ency/article/000552.htm) (MedlinePlus, US National Library of Medicine, 2026); [Hemolytic-uremic syndrome: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000510.htm) (MedlinePlus, US National Library of Medicine, 2026); [Atypical hemolytic-uremic syndrome: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/atypical-hemolytic-uremic-syndrome/) (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.

---
Source: https://durgical.com/en/general-pathology/thrombotic-microangiopathies-ttp-vs-hus/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/thrombotic-microangiopathies-ttp-vs-hus/