non-allergens like glycerin. The majority of people do react to histamine and do not react to glycerin. If the skin does not react appropriately to these allergens then it most likely will not react to the other allergens. These results are interpreted as falsely negative. Delayed reactions tests The patch test uses rectangles of special hypoallergenic adhesive tape with different allergens on them. The patch is applied to the skin, usually on the back. The allergens on the patch include latex, medications, preservatives, hair dyes, fragrances, resins, and various metals. Patch testing is used to detect allergic contact dermatitis but does not test for hives or food allergy. Skin end point titration Also called an intradermal test, this skin end point titration (SET) uses an intradermal injection of allergens at increasing concentrations to measure allergic response. To prevent a severe allergic reaction, the test is started with a very dilute solution. After 10 minutes, the injection site is measured to look for growth of wheal, a small swelling of the skin. Two millimeters of growth in 10 minutes is considered positive. If 2 mm of growth is noted, then a second injection at a higher concentration is given to confirm the response. The end point is the concentration of antigen that causes an increase in the size of the wheal followed by confirmatory whealing. If the wheal grows larger than 13 mm, then no further injections are given since this is considered a major reaction. Preparation There are no major preparations required for skin testing. At the first consult, the subject's medical history is obtained and physical examination is performed. All patients should bring a list of their medications because some may interfere with the testing. Other medications may increase the chance of a severe allergic reaction. Medications that commonly interfere with skin testing include the following: Histamine antagonists like Allegra, Claritin, Benadryl, Zyrtec Antidepressants like Amitriptyline, Doxepin Antacid like Tagamet or Zantac Patients who undergo skin testing should know that anaphylaxis can occur anytime. So if any of the following symptoms are experienced, a physician consultation is recommended immediately: Low grade Fever Lightheadedness or dizziness Wheezing or Shortness of breath Extensive skin rash Swelling of face, lips or mouth Difficulty swallowing or speaking Contraindications Even though skin testing may seem to be a benign procedure, it does have some risks, including swollen red bumps (hives) which may occur after