New Reagents Now in Use for Anti-Myeloperoxidase (MPO) and
Anti-Proteinase 3 (PR3) Detection

Effective immediately, new enzyme immunoassay reagents for anti-MPO and anti-PR3 (confirmatory tests for anti-neutrophil cytoplasmic antibody (ANCA)), are in use in Immunopathology Laboratory. This change is necessary due to the discontinuation of production of the previous reagents.

The sensitivity and specificity for ANCA-associated necrotizing vasculitides (including Wegener’s granulomatosis, microscopic polyarteritis, Churg-Strauss syndrome and pauci-immune necrotizing segmental crescentic glomerulonephritis) of the new and old reagents were compared in our laboratory on 253 patients whose sera were submitted for ANCA testing and whose final diagnosis was available. The diagnosis of ANCA-associated vasculitis of one of the types listed above was established in 48 of these patients. Approximately one-half of these patients had P-ANCA and one-half had C-ANCA.

Test New (%) Old (%) New (%) Old (%)
Sensitivity 86.2 86.2 76 96
Specificity 98.3 97 100 97.8
Positive predictive value 86.2 78.1 100 82.8
Negative predictive value 98.3 98.3 97.5 99.6

The predictive value of a positive anti-MPO or anti-PR3 EIA for the diagnosis of vasculitis is better for the new tests than the old tests while the predictive value of a negative test for absence of vasculitis was nearly the same for both tests.

New Normal Range:
Both anti-MPO and anti-PR3 now have a normal range of less than 20 units. Results >20 are considered positive.

Test schedule:
Both tests are routinely performed on Tuesdays and Fridays with results available in the late afternoon.

Specimen required:
Serum, (red top tube, 5-10 ml).

Questions or comments:
James A. Goeken, M.D. (6-1966) or Lisa Horning, SI (ASCP)