Even the best tests for food allergies have never been 100 percent accurate. At present, the most reliable is skin testing: injecting a small amount of a diluted allergen under the skin and then watching to see whether any local redness, itching or swelling develops. These are signs of allergy, but they do not necessarily establish a cause-and-effect relationship with any symptoms or conditions. A less accurate test (RAST) involves mixing a patient's blood sample with a suspected allergen to observe antibody binding.
The latest development in food allergy testing is a new device called a "lab on a chip" created by Christopher Love, an assistant professor of chemical engineering at the Massachusetts Institute of Technology. This high-tech approach involves separating out white blood cells from a sample of a patient's blood and then exposing these cells to a specific allergen - milk, for example, or peanuts or soy. The device screens for small proteins called cytokines, compounds produced by white blood cells that help recruit other immune cells to join in an allergic reaction.
Using a technique known as "microengraving," the researchers make "prints" of the cytokines produced by each cell onto the surface of a plastic slide. In this way, the amount of cytokine each individual cell secretes can be precisely measured. This new method is being tested in a study at Children's Hospital in Boston. First, kids with milk allergies are given small amounts of milk to desensitize their immune systems to the milk. Then, using the new technology, the investigators track changes in the patients' cells.
If studies show that it works, this method will enable doctors to reliably diagnose food allergies with a simple blood test. For now, if you think a particular food is causing symptoms, your best bet is to do an elimination diet. Omit a suspected problem food for several weeks, then add it back and note whether symptoms correlate with its presence or absence in the diet.
Andrew Weil, M.D.