Contribution of Reflex MPO/PR3 Testing in Anti-neutrophil Cytoplasmic Auto-Antibodies Positive Sera: An Indian Perspective

• Main Authors: Nividha Fernandes, Rupal Mistry, Vidya Nerurkar, Simi Bhatia
• Format: Article
• Language: English
• Published: Light House Polyclinic Mangalore 2016-07-01
• Series: Online Journal of Health & Allied Sciences
• Subjects: Anti-neutrophil cytoplasmic antibodies; myeloid enzymes; MPO; PR3
• Online Access: http://www.ojhas.org/issue58/2016-2-2.html
• ISSN: 0972-5997; 0972-5997

Background: Anti-neutrophil cytoplasmic antibodies are serological markers of primary systemic vasculitis. Antigen-specific tests such as ELISA to detect antibodies directed against the myeloid enzymes, MPO and PR3 are essential in addition to screening by indirect immunofluorescence. Study was undertaken to 1) evaluate the diagnostic value of ANCA measurement by IIF, coupled with reflex anti-PR3 (for c-ANCA) and anti- MPO (for p-ANCA) ELISA for ANCA positive specimens, and 2) evaluate the utility of testing specimens simultaneously by all 3 tests, i.e. IIF, MPO and PR3 ELISA. Methods: The study was a retrospective study performed at a CAP and NABL accredited private reference laboratory in Mumbai in a community setting. A total of 23,920 serum specimens from patients with suspected small vessel vasculitis were tested for ANCA by IIF over a period of 5½ years. Of these, 855 specimens (3.57%) (Group I) had a pre request for anti-MPO or anti-PR3 ELISA following a positive IIF-pANCA pattern or IIF cANCA pattern respectively. Group II comprised another 52 specimens which had a pre-request for all 3 tests i.e. IIF, MPO and PR3 ELISA simultaneously, irrespective of the IIF positivity. Results: ANCA seroprevalence was 31.11% in group I with predominant p- ANCA pattern (65.41%). p-ANCA was more frequent in females and c-ANCA in males. Anti-MPO and anti-PR3 positivity was 23.56% and 36.95% respectively, highlighting the non-specific nature of IIF-ANCA. Anti-MPO & anti-PR3 positivity was lower in females (21.10% and 31.70%, respectively) as compared to males (27.69% and 41.17%, respectively). Simultaneous performance of the three tests in Group II did not yield any significant advantage over reflex testing. Conclusion: Utility of reflex testing of IIF-ANCA positive specimens to MPO/PR3 ELISA is re-inforced in the Indian population. However, test requests for using the reflex algorithm are low. Prescribers must thus be encouraged to follow the reflex algorithm for patient benefit.