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 it in 3D — Insight Kidney (AR) ↗Android

All three shred red cells, drop platelets and injure organs (a thrombotic microangiopathy). ADAMTS13 and stool testing separate them — and because the treatments differ completely, those tests come before assuming a cause.

Go deeper

3 layers below. Open any one.

Three findings travel together: broken red cells (shredded as they pass damaged vessels — seen as fragments on the smear, a high LDH, a low haptoglobin), low platelets (used up in the clots), and acute kidney injury. Arriving together, that pattern is what should trigger the questions below — not each finding managed on its own.

Strong evidence The look-alike that must be excluded first is TTP: a very low ADAMTS13 level means TTP, not aHUS, and the treatment is different — so that test belongs before anyone assumes. The other cousins: typical (STEC) HUS, usually a child after an E. coli gut infection with diarrhoea; and DIC, clotting driven by something else. Getting this fork right is the whole game.

The driver is dysregulation of the alternative complement pathway — an inherited difference in one of its regulators (Factor H, Factor I, MCP, C3, Factor B) or an antibody against Factor H. Strong evidence Blocking complement at C5 (eculizumab, ravulizumab) transformed the outlook; plasma exchange was the older mainstay, and genetic testing guides the plan. This connects to C3G — 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.