Significant percentages of patients with certain diseases develop auto-antibodies (auto-Ab) against cytoplasmic constituents of the two peripheral-blood leukocytes (WBCs), neutrophiles and monocytes. When to use this test and the interpretation of what it means is totally dependant on the spectrum of findings in a particular case AND how the particular diagnostic specialist factors/weighs the test results among all other factors. Positivity tends to imply a disease with a blood-vessel-inflammatory (vasculitis) component.

The IFA (indirect fluorescence Ab) ANCA test is a visual test using a fluorescent microscope (patient's Ab-containing serum vs. neutrophiles substrate fixed on a glass slide).  And the IFA method is the most sensitive method⁴ for detecting ANCA; therefore, it picks up the most "false positives". IgG antibody (Ab) class ANCA is seen in test patterns that are either cytoplasmic (C-ANCA), atypical (C-ANCA [atypical]), perinuclear (P-ANCA), and atypical ANCA (x-ANCA). [There are some IgM and IgA C-ANCAs⁴] The ANCA test is most useful in patients with blood in sputum (hemoptysis) and blood in urine (hematuria)...possible indications of systemic vasculitis (as are skin purpura, blood in stool [hematochezia], and retinal hemorrhages). It also has use in inflammatory bowel disease (IBD) and auto-immune hepatitis (AIH) diagnosis. [warning] 

The test quickie capsule: (1) C-ANCA positivity is usually directed at PR3 and used to support Dx of Wegener's; (2) P-ANCA positivity is usually directed to MPO and used to support Dx of immuno-vasculitis, glomerulonephritis, C-S syndrome, polyarteritis nodosa, SLE, and RA

Situations having negative or undetected levels of Ab:

• true negative test
• rheumatoid vasculitis cases may be negative
• almost all of the below when low-grade, inactive, in remission
• some advise that an ANCA determination not be "called" negative unless IFA, PR3, and MPO tests are, all 3, negative.

• C-ANCA (95% of positives are specific for PR-3 [proteinase 3] by EIA or ELISA test methods); positive IFAs should be tested for PR-3 specificity; positivity is a finely granular cytoplasmic fluorescence correlating with a serine protease in the azurophilic granules and lysosomes in polys & monocytes, respectively and visualized as interlobular fluorescent accentuation in polys⁴:
  • Wegener's granulomatosis (WG): NOTE that IFA is 90-98% sensitive for active, classical WG (and negativity in this situation is rare). [About 90% are PR-3 positive and less than 10% MPO positive⁴] So, a negative almost rules out active, classical WG. Serial negatives confirm the rule out. Only 65-70% of limited WG are positive, and less than 35% of any types of WG in remission are positive. Re-institution of immunosuppressive therapy is not recommended on sole basis of rising titers following a period of remission. About 10% WG have anti-GBM Abs. Histopathology: look for vasculitis, geographic necrotizing granulomatous lesions, and hyperchromatic giant cells; look for histologic variants of bronchocentric WG [LMC-04-3602], eosinophilic WG, BOOP-like WG, and alveolar hemorrhage and capillaritis WG (a more fulminant type).
  • small vessel vasculitis/microscopic polyarteritis nodosa (MPA)/microscopic polyangiitis [30% of cases PR3 positive]
  • Churg-Strauss syndrome (asthmatics; usually blood eosinophilia)
  • "false positives" [not WG]
    • Kawasaki disease
    • small vessel vasculitis in  cystic fibrosis
    • atrial myxoma
    • rheumatoid arthritis (need not be vasculitic)
    • polyangiitis overlap syndrome
    • idiopathic crescentic glomerulonephritis
    • classic polyarteritis nodosa (but positivity so rare in this disease that great caution urged in making a diagnosis in the face of a positive ANCA)
    • alveolar hemorrhage syndromes with or without glomerulonephritis
    • peripheral neuropathy
    • infections (TB, HIV, endocarditis)
    • nasal septal perforation
    • drug-induced WG-like disease (retinoids, alpha methyldopa, propylthiouracil)
    • MGUS (monoclonal gammopathy of uncertain significance)
    • neoplastic diseases
  • technical false positives⁴:
    • calling cytoplasmic positivity "positive"  when it does not accentuate between the nuclear lobes
    • calling cytoplasmic positivity "positive"  when it does not occur in 95% or more of polys
    • calling cytoplasmic positivity "positive"  when it is not limited to polys
    • calling cytoplasmic positivity "positive"  when it is a heterogeneous type of fluorescence

•  P-ANCA (11-98% of positives are specific for MPO [myeloperoxidase] by EIA or ELISA test methods); IFA positivity is diagnostically nonspecific⁴; MPO-specific positivity is an artifact of ethyl alcohol substrate fixation and is not seen with formalin-fixed substrate. The cytoplasmic granules are disrupted by the alcohol, leave their normal  location, and cluster about the nucleus (not so with formalin fixation where remains as cytoplasmic fluorescence⁴).

  There are many non-MPO P-ANCAs, including those directed at other poly cytoplasmic enzymes (elastase, lactoferrin, lactoperoxidase, lysozyme, azurocidin, or cathepsin G), ANA, & granulocyte-specific ANA [GS-ANA]⁴:

  • Churg-Strauss syndrome (C-Ss) of allergic granulomatosis (a syndrome of asthmatics)
  • necrotizing and crescentic glomerulonephritis (n/cGN)
  • small vessel vasculitis/microscopic polyarteritis nodosa (MPA)/microscopic polyangiitis [60% of cases MPO positive]
  • "false positives" [not  C-Ss, n/cGN, or MPA]
    • systemic polyarteritis nodosa (but positivity so rare in this disease that great caution urged in making a diagnosis in the face of a positive ANCA)
    • Goodpasture's syndrome/anti-GBM-positive renal disease
    • 11%  of cases of giant-cell arteritis
    • giant-cell arteritis
    • Felty's syndrome
    • atypical pneumonia cases
    • post-streptococcal glomerulonephritis
    • systemic lupus erythematosus
    • mixed connective tissue disease (MCTD)
    • about 25% of WGs have this MPO positivity
    • MPO ANCA develops in many people on hydralazine therapy⁴

• C-ANCA, atypical type of positivity is a flat, nongranular, diffuse cytoplasmic fluorescence without central interlobular accentuation.
• atypical ANCA (x-ANCA; atypical P-ANCA; "snow-drift pattern"; UC-ANCA) refers to any positive cytoplasmic fluorescent pattern than the above 3. When IF is "very perinuclear" positive and MPO negative:
  • auto-immune hepatitis (AIH), 50% of cases¹ [biopsies tend to show a very "lupoid" heavy plasma cell infiltrate ; all cases of AIH will be positive for ASM, AMA, or UC-ANCA]
  • ulcerative colitis (UC), some 70% of cases¹
  • systemic lupus erythematosus
  • <10% of Crohn's¹
  • primary biliary cirrhosis (PBC)
  • primary sclerosing cholangitis (PSC), 70% of cases¹

References:

1. James A. Goeken, MD, immunopathologist & director of immunopathology lab at the U. of Iowa Hospitals and Clinics (Sept. 2000-present, personal communications).

2. CAP TODAY, June 1998 issue

3. "Vasculitis" Seminars in Diagnostic Pathology, Feb. 2001

4. Clinical Diagnosis & Management by Lab. Methods [text], JB Henry, page 992-993, 2001 edition.

5. HAPS web site

Other names for this exact or approximate test  are:   

1. ANCA
2. A-ANCA
3. C-ANCA
4. C-ANCA, atypical
5. P-ANCA
6. UC-ANCA
7. x-ANCA
8. PR3
9. MPO