In about half the cases, nothing happens. The children are fine to eat the food many have been avoiding for years.

"Parents are very happy because it's a life change," said nurse Tricia Ruhland. They no longer have to analyze food labels, agonize over accidental exposure or send special snacks to school. Many, she said, head straight from the doctor's office to Dairy Queen for a Peanut Buster Parfait.

Food allergies are often misdiagnosed, leaving many parents needlessly worrying about dangerous reactions and painstakingly monitoring food, said Dr. Leonard Bacharier, director of pediatric allergy and immunology at Washington University School of Medicine. "It's a big, ugly issue. We deal with it every day."

A key reason, he said, is many parents rely solely on the results of blood or skin tests, which are increasing in use because of easier access. Blood tests measure IgE antibodies, chemicals present during an allergic reaction. Skin tests involve measuring hives that result from pricking the skin with food extract.

But experts agree blood and skin tests are not reliable. Several recent reports have focused on tests for peanut allergies, a common food allergy one study shows increased twofold among children from 1997 to 2002. Allergies to peanuts and tree nuts are usually lifelong and the leading cause of fatal and near-fatal food allergic reactions. Misdiagnoses appear to be one of many factors behind its increase.

In a study published last month in Journal of Allergy and Clinical Immunology, researchers from the University of Manchester performed food challenges with 79 children who had positive skin or blood tests for peanut allergy. A huge portion — 66 — were found not to be allergic. The findings confirm two studies released in 2007 out of Sydney Children's and Johns Hopkins hospitals reporting large discrepancies in the results of skin and blood tests for peanut allergies.

The tests can be wrong because the presence of antibodies doesn't always mean a person will experience symptoms, Bacharier said. "In some people, these antibodies cause disease, and in other people, they don't."

A history of reactions to food must be taken into account, he said. However, many parents seek the tests because a sibling has an allergy or other vague symptoms. Or a pediatrician will screen for food allergies when a patient comes with suspicions of hay fever or a reaction to the cat. Parents are suddenly sent down a road with no easy answers.

"The problem is when patients have a food allergy test done without clear reason for doing one," Bacharier said. "These tests are wrong. They give bad advice all the time. When you order one, you have to deal with the result."

Alison Fox, 33, went to the doctor concerned her son was allergic to tomatoes. She returned with positive skin and blood tests for allergies to peanuts, peas and eggs. Her then 3-year-old son had been eating those things with no problem.

The news was disconcerting, Fox said. Her doctor told her the allergy might manifest with continued exposure. "I start freaking out, thinking well, maybe the next time he eats peanuts, he's not going to be able to breathe," she said.

Because Fox was certain of her son's food history, an allergist was willing to do a food challenge in his office. She was lucky to alleviate her fears within a couple of weeks and determine he was not allergic.

Parents with unclear cases, however, must live for months restricting their child's diet. They are unsure when or if their child last ate the food in question, or have a toddler who has never tried peanuts or eggs. In those cases, the hospital is the safest place for a food challenge, but the wait is long. Getting an appointment at Cardinal Glennon Children's Medical Center and St. Louis Children's Hospital can take over a year.

Food challenges are labor-intensive and time-consuming. Patients get 11 doses of food in increasing amounts every 15 minutes. They start their day at 8:30 a.m. and can't leave until six hours later. For some, the prospect is too daunting.

Help may lie in a more accurate blood test. The company Phadia AB has developed a test that can differentiate between the peanut's dangerous and benign antibodies. It can predict whether an allergic reaction will develop with more than 95 percent certainty, said Dr. Henry Homburger, medical director of Phadia's U.S. laboratory. The test is not yet approved by the Food and Drug Administration.

"It would be nice if they were able to advance diagnostics so we could have a lower rate of false-positive results," Bacharier said.

Meanwhile, parents like Lori Kampwerth, 29, lived over a year restricting peanuts from the diet of her 3-year-old daughter, Ellie. When Ellie was 15 months old, she developed splotches on her face after she might have eaten peanut butter cereal at a baby sitter's. She had never eaten peanuts before, so a doctor did a skin-prick test. She tested positive.

The only way to determine whether Ellie was truly allergic was with a food challenge, which she finally passed last October. Ellie now enjoys kid-favorite peanut butter candy, crackers and granola bars. The family was able to ditch the epinephrine injections kept in case of emergency. Said Kampwerth, "It's a big relief."