The pANCA test has 60%-90% sensitivity for microscopic polyangiitis, but poor sensitivity, as the test can be positive in rheumatoid arthritis and several other CTDs. However, the specificity for microscopic polyangiitis improves to greater than 95% in the setting of both positive pANCA and antimyeloperoxidase ELISA tests.
The acute phase reactants – C-reactive protein and ESR are useful in assessing patients with a suspected malignancy or infection, as well as in those in whom inflammatory arthritides or vasculitis is a concern. A CRP greater than 1.0 mg/dL indicates significant inflammation, and a value in excess of 10 mg/dL is due either to metastatic cancer, bacterial infection, or systemic vasculitis. And if both the ESR and CRP are normal, the probability that a patient has a vasculitis is "incredibly low," Dr. Janson said.
At least 80% of patients with polymyalgia rheumatica will have an elevated ESR, and the CRP should be elevated in those that don’t.
Dr. Janson reported having no relevant financial conflicts.