A 54-year-old man is evaluated for cutaneous vasculitis and peripheral nephropathy. Because of concomitant renal dysfunction, he undergoes kidney biopsy that shows glomerulonephritis. Cryoglobulins are demonstrated in the peripheral blood. Which of the following laboratory studies should be sent to determine the etiology? 

A. Hepatitis B surface antigen 

B. Antineutrophil cytoplasmic antibody (ANCA) 

C. Hepatitis C polymerase chain reaction 

D. HIV antibody 

E. Rheumatoid factor

The answer is C. (Chap. 385) The most common manifestations of cryoglobulinemic vasculitis are cutaneous vasculitis, arthritis, peripheral neuropathy, and glomerulonephritis. The demonstration of circulating cryoprecipitates is a critical component of the diagnosis, and often rheumatoid factor can be found as well. Because hepatitis C infection is present in the vast majority of patients with cryoglobulinemic vasculitis, infection should be sought in all patients with this clinical syndrome.