Using antineutrophil cytoplasmic antibody testing to diagnose vasculitis: can test-ordering guidelines improve diagnostic accuracy?
BACKGROUND
Antineutrophil cytoplasmic antibodies (ANCAs) are strongly associated with Wegener granulomatosis, Churg-Strauss angiitis, microscopic polyangiitis, and pauci-immune glomerulonephritis, referred to collectively as ANCA-associated vasculitis (AAVs). It is unclear how accurate ANCA measurement is for diagnosing AAV in diverse populations or whether proposed ANCA test-ordering guidelines improve test performance.


METHODS
We assembled a retrospective case series of hospitalized and ambulatory patients from 2 academic medical centers to assess the diagnostic accuracy of ANCA measurement by enzyme-linked immunosorbent assay in identifying cases of AAV. In addition, we assessed the effect of applying proposed ANCA test-ordering guidelines on test performance.


RESULTS
For ANCA testing, sensitivity was 81%; specificity, 98%; positive predictive value, 54%; and negative predictive value, 99%. There were no significant changes in operating characteristics after applying the guideline criteria. Using guidelines would have decreased ANCA test ordering by 23% and would have decreased the false-positive rate by 27%. No cases of AAV would have been missed if only patients fulfilling the guidelines were ANCA tested.


CONCLUSIONS
A positive result on an enzyme-linked immunosorbent assay ANCA test, as it is currently ordered, is not a definitive diagnostic indicator of AAV. Compliance with guidelines for ANCA testing would decrease the number of false-positive results and has the potential to reduce total test expenditures.
Mandl
Lisa A
LA
Robert B. Brigham Multipurpose Arthritis and Musculoskeletal Disease Center, Boston, Mass, USA.
Solomon
Daniel H
DH
Smith
Ellison L
EL
Lew
Robert A
RA
Katz
Jeffrey N
JN
Shmerling
Robert H
RH
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019268:Antibodies, Antineutrophil Cytoplasmic / Q000097:blood*; D003937:Diagnosis, Differential; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D008297:Male; D008499:Medical Records; D008875:Middle Aged; D017410:Practice Guidelines as Topic; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014657:Vasculitis / Q000175:diagnosis* / Q000276:immunology
D019268:Antibodies, Antineutrophil Cytoplasmic