In short
Blood and skin allergy tests measure sensitisation, not allergy. A long list of positives on a panel you did not need is one of the commonest ways these reports cause harm.
Emergency if: Swelling of the lips, tongue or throat, difficulty breathing, wheeze, or faintness after exposure — use an adrenaline auto-injector if prescribed and call emergency services now.
On your report
Total IgE, Absolute Eosinophil Count, WBC / Total Leukocyte Count, CRP
On this page
01
What the tests measure
An allergy blood test measures IgE, the antibody involved in allergic reactions. A total IgE gives one overall number; specific IgE measures the antibody against one particular substance, such as house dust mite or peanut, and is reported per allergen with a value and often a class or grade.
A skin prick test asks the same question a different way, by placing a tiny amount of allergen on the skin and measuring the wheal that develops. Both are measuring sensitisation — whether your immune system has made antibodies against something — which is related to, but not the same as, having an allergy.
02
The distinction that matters most
Allergy means you react clinically when exposed. Sensitisation means the antibody is present. Plenty of people are sensitised to foods they eat every week with no trouble at all, and a positive result in that situation is not a reason to remove the food.
This is why a positive result is only meaningful next to a history of reacting. The correct order is to test for what the story suggests, not to test broadly and then hunt for a story that fits the positives. Reports read the other way round lead to unnecessary and sometimes harmful elimination of foods, particularly in children.
03
Reading the numbers
A higher specific IgE value, or a larger skin prick wheal, makes genuine clinical allergy more likely — but the number does not predict how severe a reaction would be. Someone with a modest value can have a serious reaction and someone with a high value can tolerate the food. Treating the figure as a severity score is a common and consequential misreading.
Total IgE on its own is a poor allergy test. It rises with parasitic infection, eczema and some other conditions, and it can be normal in someone with clear-cut allergy. Its main use is as context for interpreting specific results, not as a screening test in its own right.
04
Cross-reactivity, and panels that mislead
Related proteins confuse the tests. Someone allergic to birch pollen often tests positive to apple and hazelnut; someone with dust mite allergy may test positive to shellfish. These cross-reactions can produce mild mouth itching or nothing at all, and they inflate panel results considerably.
Large untargeted panels are the main source of this problem. A panel testing dozens of allergens in someone with vague symptoms will almost always return several positives, each of which then has to be explained away. Component-resolved testing, which measures antibodies to individual proteins within an allergen, is how genuinely confusing cases are sorted out.
05
What these tests cannot do
IgE tests address immediate, antibody-mediated allergy. They say nothing about intolerances such as lactose intolerance, about coeliac disease, or about delayed reactions — all of which are diagnosed by entirely different tests. A negative allergy panel does not mean food is not causing symptoms.
IgG food antibody testing, widely sold direct to consumers, is not a validated test for food allergy or intolerance; IgG to food generally reflects exposure rather than disease. Hair analysis and similar consumer tests have no role either. The definitive test where the picture is unclear remains a supervised oral food challenge.
06
Using the result well
A positive result that matches a clear history confirms what is already suspected and makes avoidance advice specific. Where confirmed food allergy carries a risk of severe reaction, an adrenaline auto-injector, a written action plan, and training for family or school matter far more than the exact IgE figure.
Results also change over time, particularly in children, where milk and egg allergies are often outgrown. Repeat testing at intervals, and sometimes a supervised challenge, is how a food is safely reintroduced rather than avoided indefinitely on the strength of an old report.
When to act
Routine — see a doctor
A positive result for a food you eat regularly without any reaction: do not remove it on the strength of the report — discuss what the result means first.
Same-day — call promptly
Hives, vomiting or wheeze occurring reliably after a particular food, so that a proper assessment and an action plan can be arranged.
Emergency — act now
Swelling of the lips, tongue or throat, difficulty breathing, wheeze, or faintness after exposure — use an adrenaline auto-injector if prescribed and call emergency services now.
Values mentioned in this story
Each one opens a visual guide with its normal range and what moves it — upload a report and we place your own numbers on the same scale.
Sources
- Allergy Blood Test — MedlinePlusmedlineplus.gov
- Allergies — MedlinePlusmedlineplus.gov
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