Fx5E Food Allergy Test: What It Is & Results

A mother recently brought her 18‑month‑old son to see me because his cheeks turned red and blotchy every time he ate scrambled eggs. She was worried, exhausted from keeping a food diary, and needed answers. In cases like this – especially when symptoms appear shortly after meals – I often start with a reliable first‑line test: the fx5E food allergy screening panel.

What Is the fx5E Food Allergy Screening Panel?

The fx5E is a blood test that measures immunoglobulin E (IgE) antibodies against six of the most common food allergens in childhood and adulthood: egg white, cow’s milk, codfish, wheat, peanut, and soybean. It uses the ImmunoCAP® technology, a highly standardised method that gives quantitative, reproducible results.

In my practice, I explain to patients that the fx5E is not a “diagnosis” of allergy, but a screening tool. A positive result tells us that the immune system has made antibodies to one or more of these foods – which increases the probability of a true allergy. A negative result makes clinical allergy much less likely, though it doesn’t rule out every type of food reaction.

Why Would a Doctor Order This Test?

I typically order the fx5E when a patient – especially a child – has had one or more of the following after eating a meal:

• Hives (urticaria) or flushing
• Eczema flare‑ups
• Nausea, vomiting, or diarrhoea
• Wheezing or difficulty breathing (in more severe cases)
• Angioedema (swelling of lips, tongue, or eyelids)

I also use it as a baseline panel when a child has atopic dermatitis and we suspect food triggers but aren’t sure which ones.

What Foods Are Tested in the fx5E Panel?

The panel includes the six foods listed below. Each one is a common trigger, especially in infants and young children.

Reference Ranges for fx5E (IgE Levels)

Results are reported in kU/L (kilo‑units per litre). Lower levels indicate less sensitization. The table below shows typical cut‑offs used in our laboratory – though always check the reference range provided by your own lab, as assays can differ.

How Is the fx5E Test Performed?

The test requires a simple blood draw – no special preparation needed. Your doctor will send the sample to a laboratory that uses the ImmunoCAP method. Results usually come back within 3–5 working days.

One thing I always tell my patients: you do not need to stop eating the suspect foods before the blood test. Unlike skin prick testing, the IgE antibody level is not significantly affected by recent ingestion. However, do not stop any medications unless your doctor tells you to.

What Do Positive and Negative Results Mean?

Negative result (all allergens < 0.35 kU/L)

It is very unlikely that your symptoms are due to an IgE‑mediated allergy to any of the six foods in the panel. However, non‑IgE‑mediated reactions (e.g., food protein‑induced enterocolitis syndrome) or other causes (e.g., intolerance, coeliac disease) are still possible. In my experience, a negative fx5E is very reassuring, and I often move on to non‑allergic explanations.

Positive result (one or more allergens > 0.70 kU/L)

This indicates sensitization – the immune system has made specific IgE antibodies. But about 30–50% of sensitised children can eat the food without a reaction (false positives). Therefore, a positive result alone is not a diagnosis. I always refer for a specialist allergy consultation, where an oral food challenge or component‑resolved diagnostics (e.g., Ara h2 for peanut) can clarify the risk.

Is the fx5E Panel Accurate?

For screening, the fx5E has a very high negative predictive value – meaning if it is negative, you almost certainly do not have an IgE‑mediated allergy to those six foods. Its positive predictive value is modest, which is why we do not rely on it alone. In my practice, I view it as the “first pass” test: it helps me decide who needs more detailed investigation.

fx5E During Pregnancy

Pregnant women can safely have the fx5E test. There is no risk to the foetus from a blood draw. However, I rarely order a food allergy panel during pregnancy unless there is a new, immediate‑type reaction. Hormonal changes can sometimes confuse the interpretation, so I prefer to wait until after delivery unless symptoms are severe.

Fx5E in Children: What Parents Need to Know

This is the most common scenario for the fx5E. I reassure parents that a positive result does not mean their child will grow up with a lifelong allergy. Many children outgrow milk, egg, and soy allergies. Wheat allergy often resolves by school age. Peanut and fish allergies tend to persist. After a positive screen, I always discuss a formal allergy management plan, including emergency medication (e.g., antihistamines, adrenaline auto‑injector) if needed.

Limitations of the fx5E Panel

The panel only tests six foods. If a patient reacts to a food not in the mix (e.g., tree nuts, sesame, shellfish), the test will be negative and give false reassurance. Also, the test cannot predict the severity of a reaction – people with very high IgE levels may have mild symptoms, and vice versa. That’s why clinical history remains king.

Disclaimer: This article is for educational purposes and does not replace personalised medical advice. Always discuss your results with your healthcare provider.