Complete blood count with differential; erythrocyte sedimentation rate and C-reactive protein levels

Evaluation for streptoccocal infection (i.e., throat culture for group A streptococci, rapid antigen test, antistreptolysin-O titer, and polymerase chain reaction assay)

Excisional biopsy (when clinical diagnosis is in doubt); key histologic findings are septal panniculitis, lymphocytic infiltrate with neutrophils, actinic (Miescher's) radial granulomas, absence of vasculitis, and no organisms

Clinical suspicion of chronic disease (e.g., sarcoidosis, tuberculosis); purified protein derivative test, chest radiography

Stool culture and evaluation for ova and parasites in patients with diarrhea or gastrointestinal symptoms; consider evaluation for inflammatory bowel disease