Looking for specific IgE to any allergen via in-vitro testing (blood) is like looking for a grain of sand on a large beach. Whether it be paper disc technology (RAST) or ImmunoCAP, it does not matter. It's not going to pick it up unless there are plenty of those grains available . . . . . . usually and only in a highly allergic individual. In-vitro will still be negative in most cases, with in-vivo (skin tests) being positive. Forego the expense of in-vitro.