Laboratory testing in the evaluation and diagnosis of vasculitis.

A multitude of tests are available for the diagnosis and management of the vasculitides. Most of them are nonspecific but provide useful information that, when appropriately used in conjunction with the patient's history and physical examination can be of great assistance in arriving at a final diagnosis. In addition, information gathered may be of great help in monitoring disease activity and clinical response to therapy, in indicating the presence of specific organ system involvement, in monitoring toxicity of medication used, and in assessing prognosis. Serial measurements of acute phase reactants, complete blood cell count with differential, biochemistry profiles, urinalysis, and C3 and C4 levels should be obtained in all patients. Antineutrophil cytoplasmic antibodies (ANCA) determination provides valuable information and is highly specific for the diagnosis of small-vessel vasculitides, particularly Wegener's granulomatosis and microscopic polyangiitis. ANCA levels can be particularly useful to assess disease activity in these disorders. Hepatitis-B and, more importantly, hepatitis-C testing is extremely useful, particularly in the presence of liver involvement and associated risk factors. Angiographic studies may confirm the diagnosis, particularly if there is laboratory and clinical evidence of specific organ involvement. It should be noted, however, that angiography may be normal even when vasculitis is present, or the findings may be nonspecific. A definite diagnosis is provided by a tissue biopsy. This should be performed whenever there is access to clinically affected tissue.