Diagnostic Use
Anti-neutrophilic cytoplasmic antibodies (ANCA) represent a group of autoantibodies directed towards the cytoplasmic components of the neutrophilic granulocytes and monocytes. Using IFA techniques, two main patterns are recognised (a) a cytoplasmic [C-ANCA] and (b) perinuclear [P-ANCA] type. The main antigen for C-ANCA is proteinase 3 [PR3], a serine proteinase present in primary granules. P-ANCA patterns in general are due to antibodies directed against myeloperoxidase [MPO]. Problems exist in the interpretation of IFA patterns, due to antibodies versus lactoferrin, elastase, cathepsin-G and lysozyme resulting in P-ANCA patterns. Granulocyte specific antinuclear antibodies (GS-ANA) will also result in IFA patterns indistinguishable from P-ANCA. Use of MPO-ANCA and PR3-ANCA in conjunction with the classical ANCA IFA and ANA IFA techniques allows a greater level of discrimination when considering the clinical implication of ANCA results.
Interpretation
Documented specific clinical indications for ANCA is presented in the following Table. MPO-ANCA and PR3-ANCA are reliable serologic markers in the diagnosis of vasculitidies. PR3-ANCA is the classical autoantigen in GPA with a clinical specificity of greater than 95%. MPO is mainly present in MPA (70%).
| Disease |
ANCA IFA pattern |
Target Antigen |
| Systemic Vasculitic |
| GPA |
C-ANCA, rare P-ANCA |
PR3, rare MPO |
| MPA |
C-ANCA, P-ANCA |
PR3, MPO |
| EGPA |
P-ANCA |
MPO |
| Polyarteritis nodosa |
Rare ANCA |
Rare MPO and PR3 |
| Unclassified vasculitidies |
Rare |
No PR3 and MPO |
| Collagen / Rheumatic |
| RA |
GS-ANA, P-ANCA |
Unknown, ANA, rare MPO, lactoferrin |
| SLE |
P-ANCA |
Rare MPO, lactoferrin |
| Others |
| Ulcerative colitis |
P-ANCA |
Cathepsin G, lactoferrin and other
unknown antigens |
| Morbus Crohn |
| Chronic Hepatitis |
Reference Intervals
PR3-ANCA and MPO-ANCA
Due to (a) the use of arbitrary reporting units and (b) lack of harmonisation across diagnostic assays for MPO and PR3 antibodies it is strongly recommended that comparison of reported absolute numeric values across different assays / platforms be avoided for patient monitoring purposes.
Normal : < 20 AU/mL
Borderline: 20-25 AU/mL
Abnormal: >25 AU/mL
Test Method
Multiplex/Luminex
CARIS/FIDIS automated processing
Routine requests:
Serum are screened by indirect immunofluorescence (IIF), and specific antibody tests for PR-3 and MPO are performed on positive samples using luminex methodology.
If there is nothing documented on the request form to indicate either "rapid" or "urgent" then treat as a routine request.
Turnaround time: 2-3 days (Negative result), within 1 week for IIF reactive sera IIF C-ANCA IIF patterns are strongly associated with GPA [Granulomatosis with Polyangiitis, previously Wegener's Granulomatosis] (positive in 85 to 100% of patients with active generalised disease, less frequently in patients with limited disease). The target antigen giving a C-ANCA IIF pattern is PR3 (Proteinase 3).
P-ANCA IIF patterns are seen in the following SVV's:- MPA microscopic polyangiitis, idiopathic necrotising and crescentic glomerulonephritis (pauci-immune GN), EGPA (Eosinophilic Granulomatosis with Polyangiitis, previously Churg-Strauss syndrome). However, they can also be present in several non-SVV related diseases. The target antigen giving a P-ANCA pattern in a SVV disease is MPO (Myeloperoxidase).
In patients not under treatment with a known SVV, a negative IIF result (both patterns) excludes an ANCA-mediated vasculitic disease.
Limitations / Interference
Grossly haemolysed and/or high lipaemic serum specimens.