What about cephalosporins?
PCN related compounds are produced by the cephalosporium mold and early cephalosporins contained trace amounts of PCN - likely leading to an overestimation of cross-reactivity in the past.
Currently, no cephalosporin allergy skin test exists in the US. Assays for IgE antibodies to cephalosporins are in use in Australia. The clinical significance of this assay is unclear at this time. Major (cephalosporoyl) and minor (cephalosporanyl) determinants for cephalosporins may be used for skin testing in the near future.