What's atypical hemolytic uremic syndrome?
Atypical hemolytic uremic syndrome (aHUS) is a rare, life-threatening disorder in which an overactive complement system damages small blood vessels, causing the destruction of red blood cells, a low platelet count, and acute kidney injury.
| Also indexed as | ORPHA:2134, MONDO:0016244 |
|---|---|
| Features mapped | 8 |
| Treatments mapped | 5 |
| Published sources | 10 |
| Last reviewed | 2026-08-04 |
Signs and symptoms
Hematuria
Hematuria means blood in the urine. In aHUS it can appear along with protein in the urine when injury to the smallest blood vessels damages the kidneys.
Acute kidney injury
Damage to the small vessels of the kidney can lead to acute kidney injury, a sudden drop in kidney function that is common in aHUS.
Thrombocytopenia
aHUS lowers the platelet count (thrombocytopenia) because platelets are consumed in the damaged vessels.
Microangiopathic hemolytic anemia
In aHUS, red blood cells are torn apart as they pass through damaged small vessels, a process called microangiopathic hemolytic anemia.
Hypertension
High blood pressure is common in aHUS. As the kidneys are injured and small-vessel clotting builds up, blood pressure rises and often needs medication to control.
Elevated lactate dehydrogenase (LDH)
Lactate dehydrogenase (LDH) is an enzyme released when red blood cells and tissues are damaged. In aHUS it runs high, reflecting the ongoing destruction of red cells, and it usually falls once treatment controls the disease.
Schistocytes (fragmented red blood cells)
Under the microscope, the blood in aHUS shows fragmented red blood cells (schistocytes). These pieces form as red cells are sheared apart passing through tiny clogged blood vessels, and they are a key clue to a thrombotic microangiopathy.
Normal ADAMTS13 activity
A blood test for ADAMTS13 activity helps tell aHUS apart from a similar disease called TTP. In aHUS this activity is normal (in TTP it is severely low), so a normal result points toward a complement-driven aHUS once other secondary triggers are excluded.
How it is diagnosed
Atypical hemolytic uremic syndrome
Diagnosed using: Genetic testing.
“Genetic testing revealed that he has harbored compound heterozygous variants of the DGKE gene, namely c.12_18dupGAGGCGG (p.P7fs*37) and c.1042G>T (p.D348Y), which were respectively inherited from his father and mother.”
Atypical hemolytic uremic syndrome
Diagnosed using: Thrombotic microangiopathy.
“Atypical hemolytic uremic syndrome (aHUS) is a rare, life-threatening thrombotic microangiopathy (TMA) characterized by complement dysregulation, leading to microvascular thrombosis and multi-organ…”
Atypical hemolytic uremic syndrome
Diagnosed using: Complement genetic and autoantibody testing.
“…all patients in whom aHUS is suspected should undergo testing for complement genetic variants and…”
Atypical hemolytic uremic syndrome
Diagnosed using: Complement and complement-regulatory gene variants.
“Primary atypical hemolytic-uremic syndrome (aHUS) is associated with genetic mutations in complement and complement regulatory…”
Atypical hemolytic uremic syndrome
Diagnosed using: Anti-factor H autoantibodies.
“Another patient tested positive for anti-factor H…”
Atypical hemolytic uremic syndrome
Diagnosed using: Decreased serum complement C3.
“Four patients demonstrated decreased serum complement C3, while one maintained normal serum complement C3 throughout the course of the…”
Atypical hemolytic uremic syndrome
Diagnosed using: Diagnosis by TMA with normal ADAMTS13 and no secondary cause.
“The diagnosis of aHUS is made by the presence of TMA with normal ADAMTS13 activity without known secondary…”
Atypical hemolytic uremic syndrome
Diagnosed using: Alternative-pathway complement dysregulation.
“…aHUS is driven by uncontrolled activation of the alternative complement…”
Atypical hemolytic uremic syndrome
Diagnosed using: Distinction from STEC-HUS and TTP.
“Atypical hemolytic uremic syndrome (aHUS) is one of the thrombotic microangiopathy (TMA) syndromes characterized by thrombocytopenia, Coombs-negative hemolytic anemia, and renal dysfunction without evidence of Shiga toxin-producing Escherichia coli (E. coli) (STEC) or thrombotic thrombocytopenic purpura…”
Atypical hemolytic uremic syndrome
Diagnosed using: DGKE-associated atypical HUS.
“For infants and young children with aHUS in conjunct with nephrotic level proteinuria, variants of the DGKE gene should be…”
Treatment and management
What the research describes, not a recommendation. Treatment decisions belong with your clinician.
This covers treatments that appear in the published research mapped here. Investigational and experimental therapies are not included, so their absence is a boundary of this map, not a sign they do not exist.
Ravulizumab
Ravulizumab is a long-acting medicine that blocks the complement protein C5, given by infusion to control aHUS and protect the kidneys.
Used to help with: Atypical hemolytic uremic syndrome.
“Ravulizumab is a long-acting C5…”
eculizumab
Eculizumab is a complement C5 inhibitor used in atypical HUS. By blocking complement activity it can bring the disease under control quickly, lower the chance of progressing to end-stage kidney failure, and improve the outlook.
Used to help with: Atypical hemolytic uremic syndrome.
“She was started on treatment with plasma exchange and eculizumab, a recombinant monoclonal antibody that inhibits terminal complement activation at the C5 protein.”
Plasma therapy (plasma exchange and infusion)
Before complement-blocking drugs were available, atypical HUS was managed with plasma therapy, meaning plasma exchange and/or plasma infusion. It can still be used to remove autoantibody in aHUS caused by anti-factor H, or when a complement inhibitor is not available.
Used to help with: Atypical hemolytic uremic syndrome.
“Plasma therapy should be considered for removing autoantibody in patients with atypical HUS caused by anti-CFH or complement inhibitor is…”
Anti-C5 complement blockade as first-line therapy
Blocking complement with an anti-C5 monoclonal antibody is the first-line treatment for atypical HUS, addressing the complement overactivity that drives the disease.
Used to help with: Atypical hemolytic uremic syndrome.
“Complement blockade, anti-C5 monoclonal antibody, is the first-line therapy for patients with…”
Vaccination and surveillance with C5 inhibitors
The C5 inhibitors eculizumab and ravulizumab have transformed treatment of atypical HUS, but because blocking complement raises infection risk they require preventive vaccination and ongoing monitoring.
Used to help with: Atypical hemolytic uremic syndrome.
“C5 inhibitors, such as eculizumab and ravulizumab, have revolutionized treatment but necessitate prophylactic vaccination and ongoing clinical…”
How to read the evidence labels
Where this comes from
This guide is built from 10 published source(s). Every claim above links back to one of them. Click any source ID to read the original on PubMed.
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