Atypical HUS (aHUS)
Atypical HUS is abnormal complement activation damaging the smallest blood vessels.
Tiny clots form, shred red cells as they squeeze past, and injure the kidney. The catch: it looks like its commoner cousins, and the test that separates them has to be asked for before treatment assumes the wrong one.
See the kidney in 3D, on your phone or tablet
Insight Kidney is a free app. It shows a healthy kidney, and these diseases, in 3D you can walk around. It runs on iPhone, iPad and Android, not on Windows or Mac computers. It is large, about 1 GB, so Wi-Fi helps.
It is made by Anima Res, a German medical animation studio, and it was paid for by Novartis, who sell drugs for some of these conditions. We name who paid so you can weigh that yourself.
Go deeper
3 layers below. Open any one.Three findings travel together.
- Broken red cells, shredded as they pass damaged vessels. They show as fragments on the smear, a high LDH, which is lactate dehydrogenase, and a low haptoglobin.
- Low platelets, used up in the clots.
- Acute kidney injury.
Arriving together, that pattern is what should trigger the questions below, not each finding managed on its own.
The look-alike that must be excluded first is TTP, thrombotic thrombocytopenic purpura. A very low ADAMTS13 level means TTP, not aHUS, and the treatment is different. Strong evidence So that test belongs before anyone assumes.
There are two other cousins. One is typical HUS, haemolytic uraemic syndrome, also called STEC HUS. STEC stands for Shiga toxin-producing E. coli. It is usually a child, after an E. coli gut infection with diarrhoea. The other is DIC, disseminated intravascular coagulation: clotting driven by something else.
Getting this fork right is the whole game.
The driver is dysregulation of the alternative complement pathway. That can be an inherited difference in one of its regulators: Factor H, Factor I, MCP, C3 or Factor B. MCP stands for membrane cofactor protein. Or it can be an antibody against Factor H.
Blocking complement at C5, with eculizumab or ravulizumab, transformed the outlook. Strong evidence Plasma exchange was the older mainstay, and genetic testing guides the plan.
This connects to C3G, C3 glomerulopathy: the same alarm failing to switch off, in a different place.
Questions to bring
The ones that change what happens. Copy these, or read them out. They fit in a short visit.
- Can we run an ADAMTS13 to rule out TTP before assuming this is standard kidney disease?
- What are my C3 and C4?
- Given low platelets, broken red cells and kidney injury, should haematology be consulted for complement-mediated TMA?
The short version
- Getting ahead of it
- When broken red cells, low platelets and kidney injury arrive together, push for the right tests before treatment assumes a cause.
- Your testing regime
- ADAMTS13 (to exclude TTP), blood smear, LDH, haptoglobin, C3/C4, and a complement gene panel.
- What they don’t tell you
- ADAMTS13 must come before assuming aHUS, and genetics guide whether complement blockade is lifelong.
- What it can spawn
- Kidney failure, and recurrence — including after a transplant — if complement is not controlled.
- What it’s confused with
- TTP, typical (STEC) HUS, and DIC.
From general clinical literature; not a diagnosis; nothing here comes from any individual’s medical record.