aHUS

- Glossary

A

ADAMTS13
A metalloprotease enzyme that cleaves von Willebrand factor; deficiency is diagnostic for TTP (thrombotic thrombocytopenic purpura), not aHUS.

Alternative Complement Pathway
A part of the innate immune system that activates complement independently of antibodies. Dysregulation is central to aHUS pathophysiology.

Anti-CFH Antibodies
Autoantibodies against complement factor H, leading to uncontrolled complement activation and TMA; often seen in pediatric aHUS.

Autoimmune aHUS
Subtype of aHUS involving anti-CFH antibodies, requiring immunosuppressive treatment in addition to complement inhibition.

B

Blood Urea Nitrogen (BUN)
A test used alongside serum creatinine to assess kidney function.

C

CFH, CFI, CFB, MCP, C3, THBD
Genes coding for regulatory proteins in the complement system. Mutations in these are linked to genetic forms of aHUS.

Clinical Triad (aHUS)
Includes microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury.

Complement Inhibitors
Therapies (e.g., eculizumab, ravulizumab) that block C5 and prevent terminal complement activation in aHUS.

Complement Levels (C3, C4)
Used to evaluate complement activity; low levels may indicate activation but are not specific to aHUS.

C5b-9 (Soluble)
Terminal complement complex measured to assess complement activation; may support aHUS diagnosis and monitoring.

D

Differential Diagnosis
The process of distinguishing aHUS from other TMAs such as TTP, STEC-HUS, SLE, and DIC.

Direct Coombs Test
Used to differentiate immune hemolytic anemia from microangiopathic processes like aHUS.

E

Eculizumab
A C5 inhibitor used in the treatment of aHUS; short-acting and administered biweekly.

Endothelial Cell Dysfunction
A result of complement dysregulation in aHUS that leads to microvascular thrombosis.

F

Familial aHUS
aHUS occurring in two or more related individuals, usually with inherited complement gene mutations.

Fibrin Degradation Products (FDPs)
Used to rule out DIC in the differential diagnosis of TMA.

Full Fresh Frozen Plasma (FFP)
Used in plasma exchange (PEX) as replacement fluid during the treatment of TMA.

G

Genetic Testing
Testing for mutations in complement genes to support diagnosis and guide long-term therapy decisions in aHUS.

Glomerular Basement Membrane
A part of the kidney filtration barrier often damaged in aHUS due to microthrombi and endothelial injury.

H

Hematuria
Presence of blood in urine, often a sign of kidney involvement in aHUS.

Hemolysis
Destruction of red blood cells seen in microangiopathic processes like aHUS.

Haptoglobin
A protein that binds free hemoglobin; low levels suggest hemolysis.

I

Immunosuppressive Therapy
Used in autoimmune aHUS (e.g., with anti-CFH antibodies) along with corticosteroids and complement inhibitors.

K

Kidney Ultrasound
Imaging used to evaluate kidney structure in patients with suspected or ongoing renal dysfunction.

L

Lactate Dehydrogenase (LDH)
An enzyme elevated in hemolysis; used to monitor disease activity in aHUS.

M

Maintenance Therapy
Continued treatment (e.g., anti-C5, immunosuppressants) after achieving remission to prevent relapse in aHUS.

Microangiopathic Hemolytic Anemia (MAHA)
A form of hemolysis due to red cell destruction in the microvasculature; a hallmark of aHUS.

Membrane Cofactor Protein (MCP/CD46)
A surface complement regulator; mutations are implicated in some genetic forms of aHUS.

O

Oliguria
Decreased urine output; a sign of acute kidney injury, often seen in aHUS.

P

Plasma Exchange (PEX)
A therapeutic procedure replacing plasma to remove antibodies or abnormal complement components; used in some aHUS cases.

Peripheral Blood Smear
Microscopic exam of blood cells; used to detect schistocytes in aHUS diagnosis.

PNH (Paroxysmal Nocturnal Hemoglobinuria)
Another complement-mediated condition treated with anti-C5 inhibitors, often included in treatment studies alongside aHUS.

R

Ravulizumab
A long-acting C5 inhibitor administered every 8 weeks; used as an alternative to eculizumab.

Reticulocyte Count
Used to assess bone marrow response to anemia; increased in hemolytic anemias.

S

Schistocytes
Fragmented red cells on blood smear, indicating microangiopathic hemolysis.

Shiga Toxin–Producing E. coli (STEC-HUS)
A common cause of typical HUS, which must be ruled out in suspected aHUS cases.

Systemic Lupus Erythematosus (SLE)
An autoimmune disease that can mimic TMA; must be excluded during aHUS workup.

T

Thrombotic Microangiopathy (TMA)
A group of disorders, including aHUS, marked by thrombosis in small vessels, hemolysis, and thrombocytopenia.

Thrombocytopenia
Low platelet count, one component of the aHUS triad.

Thrombomodulin (THBD)
A complement-regulating protein; mutations can be associated with aHUS.

TTP (Thrombotic Thrombocytopenic Purpura)
A TMA condition that must be ruled out by ADAMTS13 testing in suspected aHUS cases.

U

Uremia
A clinical syndrome of kidney failure with retention of waste products, common in advanced aHUS.