Tryptase is released along with histamine in the blood during an allergic reaction. Unlike histamine, tryptase remains in the blood for a longer time, usually up to six hours. Serum tryptase test is performed to ascertain an allergic reaction. However, the test cannot detect the allergen responsible for the allergy.

Cellular allergen stimulation (CAST) test is a modern diagnostic tool for diagnosing allergens hidden in preservatives, food colors, aspirin and other drugs. It measures the levels of inflammatory compounds known leukotrienes in the blood sample. These inflammatory chemicals are released only by specific allergens such as sulfites, sodium benzoate, salicylates and tartrazine.

Histamine released in the bloodstream during allergic reactions is rapidly metabolized. It is therefore quite difficult to measure the histamine level with conventional blood testing kits. The advanced histamine release testing kit aids allergy diagnosis by measuring the histamine level in the blood. It aids diagnosis of allergic reactions that do not produce IgE. Idiopathic urticaria is usually detected through this blood test.

Double blind placebo controlled food challenge is used for diagnosing food allergies. The test is performed under the supervision of hospital staff. The patient is given capsules or broth containing the allergen or a dummy. Although this is the most reliable method of testing food allergies, the process might be risky for people susceptible to severe food allergies. This procedure can be done only in a specialty clinic equipped with resuscitation equipment. It is also a time consuming process. It might take several days to find the offending food substances.

In allergen provocation tests, the possible allergen is directly introduced in the nose, lungs or eyes and the response to the allergen is measured.

A blood test for allergy is needed when skin tests cannot be performed owing to certain skin problems such as eczema, psoriasis and hives. When a person is on an antihistamine or tricyclic antidepressant, the drug might influence the result of the skin test. Even when a person is allergic to a substance, the skin test might give a negative result. It might warrant a blood test to ascertain the cause of the allergy. However, blood tests are not as sensitive as the skin tests. They help in detecting antibodies known as immunoglobulin E (IgE), that are released in the bloodstream by the immune system of the body in response to the allergy. The blood test commonly used for diagnosing allergy is called Enzyme linked Immunosorbent Assay or ELISA.

Skin patch test is done to detect contact allergy. It is also used for diagnosing delayed hypersensitivity to food. In the test, a pad soaked in the allergen solution is taped to the skin for one to three days.

When the skin prick test fails to identify the possible allergen, you can undergo an intradermal test to verify the result of the skin prick test. In the intradermal test, instead of placing the allergen on the surface of the skin, the solution containing the possible allergen is injected deeper into the skin. If you are sensitive to the substance, a wheal will appear on the site of the injection within 15 minutes. However, the extreme sensitive nature of the test can give false positive test results.

Skin prick test helps to identify the food allergens, airborne allergens and sensitivity of a person to medicines and insect venom. Before starting the skin allergy test, at first the site of the test which is usually the arm or the back, is cleaned with alcohol. A drop of a solution containing the suspected allergen is placed on the skin. By pricking the skin with a needle, the solution is allowed to penetrate in the skin. Multiple substances can be tested simultaneously in this manner. If a person is sensitive to one of these substances, a swollen red itchy area, known as wheal, will develop at the site of the allergy test.