There is no benefit in routinely monitoring ANCA titres in patients with granulomatosis with polyangiitis.

ABSTRACT

OBJECTIVES: To analyse the link between antineutrophil cytoplasmic antibody (ANCA) levels and risk of relapse in patients with granulomatosis with polyangiitis (GPA), as the clinical benefit of monitoring ANCA levels is uncertain. METHODS: A retrospective analysis was made of all charts available from 43 patients diagnosed with GPA, fulfilling The American College of Rheumatology 1990 criteria, and followed between 1994 and 2012 at a general internal medicine department of a university hospital. Clinical and biochemical data (i.e. anti-proteinase 3 (PR3) levels) were collected and correlated. RESULTS: 43 relapses occurred in 25 patients (58.1% of 43 patients). When blood samples are routinely taken at a follow-up visit (i.e. low pre-test probability, ± 5.5%) in the GPA-population, a 75%-increase in the PR3-level or its reappearance has only limited positive predictive value (PPV 15.0% and 22.5% respectively) for predicting relapse. Adversely, when clinical suspicion of relapse is high (i.e. high pre-test probability, for example 50%), an increase of 75% or reappearance of PR3 makes relapse even more likely (PPV 77.5%, 81.6% respectively). Conversely, a high negative predictive value (NPV) of 99.3% and a negative likelihood ratio (LR-) of 0.12 suggest that, in the absence of PR3, relapse is unlikely if patients had detectable ANCAs at diagnosis. CONCLUSIONS: Routine ANCA monitoring in patients diagnosed with GPA has limited value. However, targeted determination of ANCA levels may be useful if a relapse is clinically suspected (i.e. high pre-test probability).