Myeloperoxidase is the most commonly recognised p-ANCA antigen. It is a 140kDa cationic protein found predominantly in azurophilic granules of neutrophils and monocytes.The p (peripheral)-ANCA staining pattern is an artefact produced when the MPO released fom the granules by the ethanol used in fixation of the cells is attracted to the nucleus. The enzyme which accounts for up to 5% of total cell protein generates anti-microbial chlorinated oxygen species from hydrogen peroxide produced as a result of the neutrophil respiratory burst. The autoantibodies appear to recognise conformational determinants but do not inhibit the enzyme activity. In different studies only 10-35% of P-ANCAs showed anti-myeloperoxidase activity.
An improved assay (termed MPOS) was introduced May 16 2011. Quantitative values using the new assay may vary from those obtained previously.
Specific autoantibody found in ANCA vasculitis.
p-ANCA antibodies (anti-MPO) are found in most (90%) of patients with microscopic polyarteritis and other vasculitides (70% in Churg Strauss syndrome and 20% patients with Polyarteritis nodosum). 10% of patients with Wegeners granulomatosis have anti-MPO rather than the anti-PR3 which is characteristic of this disease; the two seldom occur together.Anti-MPO are found in 65% of patients with idiopathic or vasculitis associated necrotizing crescentic glomerulonephritis. 30-40% of patients with Goodpastures syndrome have anti-MPO along with anti-GBM. these patients are generally older and have less severe renal disease than those with anti-GBM alone. Occasionally, low levels of anti-MPO can be found in other diseases (particularly chronic bacterial infections, colitis, liver disease) in the presence of other ANCAs.
Serum Separator Tube (SST)
Fluorescence enzyme linked immunoassay (Phadia Immunocap 250) : Purified human MPO protein IgG antibodies.
- Post 15 May 2011 MPOS < 3.5IU/ml
- Pre 15 May 2011 MPO < 7U/ml
Assay range notes
- Post 15 May 2011
MPOS 3.5-5.0 IU/ml equivocal; >5.0 IU/ml positive; Assay Range 0-135 IU/ml
- Pre 15 May 2011 MPO 7-10U/ml equivocal: >10U/ml positive; Assay Range 0- 600 U/ml
5 – 7 days