A 26-year-old man has had difficulty breathing through his nose for 3 years, but this problem has become progressively worse over the past 2 months. Physical examination shows glistening, translucent, polypoid masses filling the nasal cavities. Histologic examination of the excised masses shows respiratory mucosa overlying an edematous stroma with scattered plasma cells and eosinophils. Which of the following laboratory findings is most likely to be present in this patient?