Allergy & Immunology
An 18-year-old man is evaluated for recurrent infections. He was recently hospitalized for his second episode of community-acquired pneumonia caused by Streptococcus pneumoniae despite previous pneumococcal vaccination. He has required antibiotic therapy for frequent episodes of sinusitis and bronchitis. Giardiasis was diagnosed 2 years ago.
Other than a BMI of 17, today's physical examination is unremarkable. Complete blood count is normal, and testing for cystic fibrosis and HIV infection is negative.
Which of the following is most likely to establish the diagnosis?
A. Flow cytometry of peripheral blood
B. Response to intradermal skin testing with Candida antigen
C. Serum IgG, IgM, and IgA levels
D. Total hemolytic complement level
This patient likely has common variable immunodeficiency (CVID), and serum levels of IgG, IgA, and IgM should be measured to begin evaluation (C)