Pigweed is basically a small leafy plant that is often found in gardens and backyard or in abandoned fields. Sometimes it causes allergies. The common symptoms include sneezing, common cold, watery and itchy eyes. The IgE blood allergy test is basically done to determine whether one is allergic to common pigweed. This virtual free of pain lgE blood test helps to determine the presence of allergenic substances and their status. Mainly the common pigweed allergy test is done on a sample of blood to measure the status or the level of IgE antibodies present in the blood.