Skin prick using small amounts of suspect allergy triggers through the skin of the arm or back by pricking or puncturing the skin with a needle or similar device are the most commonly used allergy tests. The RAST (radioallergosorbent test) and related blood tests use radioactive or enzyme markers to detect levels of IgE antibodies are used when a skin test is difficult due to: A widespread skin rash, anxiety about skin pricks and/or potential for a sudden and severe allergic response to test allergens.