Yi Tong Vincent Aw¹, Jason Chun Lao^2,3, Richard Fulton², Jamma Li^1,3, Suran Fernando^1,2,3

¹Department of Clinical Immunology and Allergy, Royal North Shore Hospital, Sydney, Australia; ²Immunology Laboratory, Royal North Shore Hospital/NSW Health Pathology, Sydney, Australia; ³Northern Clinical School, Faculty of Medicine and Health, University of Sydney, Sydney, Australia

Introduction: Anti-neutrophil cytoplasmic antibody (ANCA) is used for ANCA-associated vasculitis (AAV) diagnosis, but often routinely ordered for suspected inflammatory bowel disease (IBD), autoimmune liver disease (ALD), and vasculitis screening in the settings of acute kidney injury (AKI), peripheral neuropathy (PN), central nervous system pathology (CNS), interstitial lung disease (ILD), haematological abnormalities (HA), coagulopathy/vasculopathy (CV), cardiomyopathy, undifferentiated inflammatory states (UIS) and rash. ANCA diagnostic utility for such indications is unclear.

 

Method: Retrospective cross-sectional analysis was performed on consecutive ANCA tests done at Royal North Shore Hospital/NSW Health Pathology from 1^st January to 21^st March 2022. Performance characteristics were calculated for ordering indications.

 

Results: 516 tests were included. ALD (N=84; 4 ALD, no AAV), UIS (N=46; 1 AAV), rash (N=44; 2 AAV) and ILD (N=21; 1 AAV) had low positive predictive value (PPV). IBD (N=18; 4 IBD, no AAV) had low sensitivity. No AAV cases arose from cardiomyopathy (N=13), CV (N=20), HA (N=21) and CNS (N=88) indications. AKI (N=107; 14 AAV) and PN (N=34; 2 AAV) had high NPV/PPV. Refining AKI orders for glomerulonephritis maintained high NPV/PPV while reducing testing by 59%.

 

Conclusion: Ordering ANCA primarily for ALD, IBD, UIS, rash, ILD, CV, HA, CNS or cardiomyopathy, is of low diagnostic utility.

Submitting author statement: The submitting author contributed to the study concept and design, data collection, analysis and writing. These elements were all original ideas of the submitting author. Generative AI was not used in the writing process.