Serum levels of specific IgE to cefaclor were significantly higher in patients with anaphylaxis than in patients with non-anaphylactic immediate HS (6.45 ± 15.6 kU/L vs. 1.73 ± 4.7 kU/L, P = 0.004) (Table 5). This evidence concerns the gene IGHE and anaphylaxis.