General Precision Point Diagnostics January 25, 2024

True food allergies are when the body develops antigens against a particular food- or a related food. Patients can be sensitive to food, they can be allergic, or they can be reactive in a different way. Sometimes patients will be surprised by a result on a food antigen test when a food that they don’t eat shows up as positive for one of the allergic markers on the test. How can that be, they think? Since a food allergy requires antigen development, then how would antigens develop if the food isn’t consumed in the first place? There are several reasons. Let’s explore them.

Ruling Out Labeled Allergens

The first thing that should be done is to rule out that a hidden allergen isn’t present in the patient’s diet. Sometimes patients will consume foods they don’t realize they are ingesting. A good example might be ingredients found in packaged foods as stabilizers, emulsifiers, thickening agents, and preservatives. Cornstarch, carrageenan (extracted from algae/moss), tapioca, arrowroot, guar gum, and gelatin are some examples. There are also ingredients that patients might not be aware are standard components of some foods, such as gluten from wheat in soy sauce, anchovy in Worcestershire sauce, and insect and plant sources for food colorings. Interview the patient about sauces and flavorings they may use and encourage them to carefully read labels to rule out the possibility of an allergen they may not be aware of.

Ruling Out Hidden Allergens

A second possibility beyond a patient simply eating a labeled allergen without being aware of it is that they could be consuming hidden allergens. Hidden allergens are different from labeled allergens because a patient won’t be able to tell from a label that the food is there, so it can be easier to miss. Dining out is particularly difficult when trying to parse out which allergens are present. Some restaurants are fantastic in providing allergen information, while others may be ill-informed or poorly communicate the information. Even careful places may need to be specifically asked and can still make mistakes. For example, a restaurant may not have a dedicated grill or fryer for different types of foods, and your fries may have been fried along with gluten-containing foods. Outside the restaurant environment, packaged foods may have been processed on machinery that also processes an allergen. Certain hidden additives don’t always have to be reported on a label, even under US or EEC guidelines if they are used in small amounts. “These “hidden” allergens include mustard, celery, spices, lupine, pea, natural food colourings, and preservatives, but can occasionally include allergenic material from contaminants such as cereal mites.”(1) It’s very likely that your patient has not been assiduously reading labels if they haven’t been antigen tested before, so make sure you go down that path first.

Ruling Out Cross-Reactivity Between Foods In The Same Family

A third possibility is that what you and the patient are seeing is cross-reactivity between foods in the same family. Foods are grouped into food families because they are related by taxonomy and share the capacity to cross-react in the creation of antibodies. Although this might be confusing in the sense that the test shows a food that isn’t normally consumed as reactive, in fact, it’s an opportunity for more effective treatment. The standard of care after a food antigen test is to place the patient on an elimination diet, where foods that have been reacted to are eliminated and gradually introduced. 

Foods in the same family that can be cross-reactive are recommended to be eliminated as well so that a more complete chance for improvement is possible. It’s better to cast a wider net- as long as that net is based on comprehensive testing that can offer guidelines for elimination based on an intersection of markers. 

For this type of testing we recommend the Precision Point Diagnostics P88 Dietary Antigen Test which evaluates all foods and for IgE, IgG, IgG4, and C3d reactions. This  allows the physician to decide which food groups should be focused on for entire elimination (particularly those associated with a high C3d result indicating systemic inflammation and a low IgG4 reaction meaning little alleviation of inflammation through that response), and which food groups can be ignored altogether or only partially decreased in the elimination diet. 

As individual foods are reintroduced, the family cross-reactivity is zeroed in on for that particular patient. 

Using the P88 Dietary Antigen Test in Practice

The Precision Point Diagnostic P88 Dietary Antigen test measures a patient’s response to IgE, IgG, IgG4, and complement (C3d) reactions to 88 of the most common foods found in the diet in one single test. The P88 Dietary Antigen Test was the first test on the market to measure and report immune complexes containing C3d. Each food on the test is evaluated against each of the markers. The 88 foods on the test were chosen to represent a spectrum of foods common in the diet to have the widest usefulness to the clinician. In addition, the range of foods on the panel can be a very good tool to pick up some foods that do not appear. Various food groups can show cross-reactivity with each other, allowing the clinician to consider foods outside the scope of the panel. It just isn’t practical, or necessary, to include 500 foods on a panel, particularly when you are providing more important data by testing four different markers, and cross-reactivity within food families allows for a wider net to be cast when diagnosing a food allergy or sensitivity.

Precision Point Diagnostics also offers a free physician’s guide to the  P88 Dietary Antigen Test, available on our website that not only describes the test in full and how to interpret it, but also contains comprehensive tables on foods that are cross-reactive classified in groups, but also a table on the interaction between specific environmental allergens and which foods they can interact with. Remember that Precision Point Diagnostics also offers environmental allergy testing.  

Although you’ll find a complete list of cross-reactive foods in the tables of the Physician’s Guide, let’s take a look at some of the interactions that might be of particular interest. 

Gluten or Wheat Allergy

A gluten or wheat allergy is one of the more important results that can be delivered. It’s most likely that both gluten and wheat will show up together as positive if either does. Sometimes, though, a patient may test positive for gluten but not wheat or vice versa. Wheat contains gluten, but gluten comes from many other grains as well. If gluten shows up but wheat doesn’t, the patient may indeed not eat wheat and the cross-reactivity just isn’t that strong. If wheat shows up, but gluten doesn’t, then it’s more likely that the patient is reacting to other compounds in the wheat. 

Mold Allergy 

Mold positivity could be a cross-reactivity with cheeses that contain mold, peanuts, melons, sake, vinegars, kombucha, alcohol, soured breads, fermented foods, cider, rootbeer, pickled and smoked meats, dried fruits, canned tomatoes, and canned juices. Why? Sometimes because the mold has contaminated the food (dried fruit and tomatoes rarely are completely mold-free), and sometimes because specialized molds are used on purpose to ferment the foods (like kombucha, sake, and soured foods). Yeast positivity can be possible because a patient is infected with Candida. Take a look at the chart and see how related foods can cross-trigger as well. Examples include almonds with peaches, asparagus with garlic or onions, avocados with cinnamon, cacao with kola nut, spinach with quinoa, etc. Take a look, the chart is fascinating!

Other Reasons For Reactions

There are times when a food won’t show up when a patient knows they are reactive. There are several possible reasons for this as well. Foods that are high in histamines (like smoked meats, cheeses, etc.) can cause a direct reaction to the histamines in the food rather than an allergic reaction to the food itself. Likewise, foods like smoked meats can be high in nitrates and nitrites, wine can be high in sulfites, etc. These chemical reactions are not allergic reactions to the foods themselves, and when an allergy doesn’t show up it can steer the patient to continue to enjoy nitrate-free meats and sulfite-free wines, for example. There can be non-allergic reactions to gluten because gluten is interfering with the ability to convert amino acids into neurotransmitters. Specific foods might cause platelet-activating factor- not an allergy, but still a noticeable reaction. Depending on the patient, other foods may be high FODMAP. The P88 Dietary Antigen Test is a powerful tool for diagnosis, but like other useful tools, sometimes it may just rule out a pathway.

Cross-Reactivity To An Environmental Allergen

The fourth possibility as to why a food that isn’t consumed by the patient may still show up in the results of a food antigen test is because of cross-reactivity to an environmental (often airborne) allergen. The Physician’s Guide to the P88 Food Antigen Test also contains a chart showing potential interactions between environmental allergens and food allergens. 

Sometimes a patient may be positive to a food they do not consume because they cross-react to an environmental allergen that they are allergic to. Take a look at the full chart in our guide. Some of these allergens are very interesting. For instance, someone who shows up as allergic to beef, but is a vegetarian might be disbelieving. It turns out that beef allergies cross-react with tick allergies. In fact, someone who doesn’t eat beef and tests positive for that food allergy should be examined for symptoms of Lyme Disease. 

Patients that don’t eat seafood but test positive to clams may be cross-reacting with an allergy to roaches. 

Latex is cross-reactive to bananas and a host of other foods. Meat allergies can be cross-reactive to animal dander. Many pollens can cross-react with fruits and vegetables. 

Maple syrup and barrel-aged products (including alcohol) may cross-react with the pollen from the trees used to age them (an ongoing area of research that is sometimes hotly disputed by the wine and spirits industry). It’s wise to consider the environmental interplay when a specific food is tested as positive for a patient who says they don’t consume that food.


Food antigen testing is a complicated business because of the complexity of the pathways whereby food allergies are formed. Knowing the interplay of foods with each other, foods with the environment, hidden food allergens, and the types of allergic reactions can make a more successful physician when treating your patients. Food allergies are as diverse as the patient, and this is why simple food tests that don’t allow for the interactions between different pathways for allergic reaction don’t tell the whole story. Elimination diets can be difficult to get patients to comply with. The more compelling you can be with your explanations to them, the greater the degree of success you are likely to have. 



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