Egg Yolk (Gal d 5) IgE Test · Blood

If you or your child reacts to eggs, knowing which part of the egg triggers the immune system changes how you eat, cook, and live. This blood test looks for IgE antibodies against Gal d 5 (chicken serum albumin), the main allergenic protein in egg yolk.

Standard egg allergy testing usually measures antibodies to whole egg white, which can miss yolk-specific patterns. A positive Gal d 5 result identifies a more specific phenotype, including people who react to both eggs and birds, and it carries useful information about how persistent the allergy is likely to be.

What This Test Actually Measures

Gal d 5 (full name: chicken serum albumin, also called alpha-livetin) is a 69,000-dalton protein found in egg yolk and also in the blood, feathers, and meat of chickens and other birds. IgE (immunoglobulin E) is the antibody class your immune system uses to flag allergens, and it is the antibody that triggers classic allergy symptoms like hives, swelling, and anaphylaxis.

Your blood sample is analyzed for IgE antibodies that specifically bind to Gal d 5. A detectable result means your immune system has been sensitized to egg yolk protein, though sensitization alone does not always mean clinical allergy.

Bird-Egg Syndrome

Gal d 5 is the defining allergen in bird-egg syndrome, a condition in which people react to both egg yolk and to bird-related exposures like feathers, bird meat, or living with pet birds. In the original study of 8 patients with bird-egg syndrome, every one of them had serum IgE to egg yolk, chicken serum, chicken meat, feathers, and Gal d 5, with reactions confirmed by oral, conjunctival, and bronchial challenges.

This pattern matters because the symptoms span both respiratory (rhinitis, asthma) and food allergy domains. If you have unexplained respiratory symptoms around birds plus food reactions to egg, a positive Gal d 5 result helps connect the two.

Gal d 5 is partially heat-labile, meaning cooking reduces but does not eliminate its allergenic activity. Heating egg at 90 degrees Celsius for 30 minutes cut IgE reactivity to Gal d 5 by 88%. Lightly cooked yolk may still trigger reactions in highly sensitive people.

Egg Allergy Persistence

In a population-based study of 451 infants, IgE sensitization to all four major egg components (Gal d 1, Gal d 2, Gal d 3, and Gal d 5) at 12 months of age increased the odds of persistent raw egg allergy at age 2 by roughly four times compared with infants without that broad sensitization pattern. Early Gal d 5 sensitization on its own showed about five times higher odds of persistent allergy, though the wide statistical range means this single-component estimate is less certain.

Across the same cohort, sensitization to Gal d 5 alone was uncommon, found in about 4% of suspected egg-allergic patients in another analysis. When present, it usually appears alongside sensitization to egg white components in children who tend to be slightly older and more strongly allergic overall.

In a separate study of 81 children younger than 2, a yolk-specific IgE level of 2.1 kU/L or lower predicted a good chance of outgrowing egg allergy, while higher values were associated with persistence. Low or absent Gal d 5 IgE, especially combined with low egg white IgE, generally points toward a milder course and a higher likelihood of tolerance over time.

How It Compares to Standard Egg Allergy Tests

For simply diagnosing whether you currently have an egg allergy, whole egg white IgE remains the workhorse and tends to perform at least as well as component testing. Component testing including Gal d 5 did not improve diagnostic accuracy over egg white IgE in the largest infant cohort that compared them head to head.

Where Gal d 5 earns its place is in phenotyping. It identifies people whose allergy involves the yolk and bird proteins specifically, and it strengthens the prognostic picture when ordered alongside Gal d 1 (ovomucoid, a marker of reactivity to baked egg) and the other egg components. In adults, egg yolk IgE testing adds little diagnostic value beyond egg white IgE, so this test is most informative when there is a specific clinical reason to look at the yolk fraction.

Tracking Your Trend

A single IgE reading is a snapshot, not a verdict. Egg-specific IgE levels typically fall over months and years in children who are outgrowing their allergy, and the rate of decline itself is informative. In a study of 124 children, the reduction in egg-specific IgE over the first 12 months after diagnosis was an independent predictor of which children would later develop tolerance.

For an active egg-allergic patient, a reasonable cadence is a baseline measurement, a recheck in 6 to 12 months, and continued annual tracking as long as the allergy remains relevant. If you are pursuing oral immunotherapy or undertaking a deliberate dietary change like introducing baked egg, retesting earlier helps confirm that the trajectory is moving in the right direction.

Modern IgE assays are technically reliable, with measurement variability under 20% in well-controlled assays for related egg components. That means a real change of 30% or more between two readings is more likely to reflect a true biological shift than lab noise.

This Test Is a Research Marker, Not a Standalone Diagnosis

Gal d 5 IgE is an emerging clinical marker without universally standardized cutpoints. Sensitization does not always mean you will react when you eat egg yolk. The gold standard for confirming any food allergy remains an oral food challenge performed under medical supervision, and a positive Gal d 5 result should be interpreted alongside your symptom history, skin prick testing, and whole egg white IgE.

When Results Can Be Misleading

A few factors can affect how to interpret a single Gal d 5 IgE reading:

• Sensitization without clinical allergy: detectable IgE to Gal d 5 does not always mean you will react to eating egg yolk. Some people have positive blood tests but tolerate the food.
• Low values in tested children: Gal d 5 sensitization is found in only about 4% of children with suspected egg allergy, so a negative result does not rule out egg allergy driven by white-fraction proteins like Gal d 1 or Gal d 2.
• Age and disease context: total IgE peaks in childhood and slowly declines with age, which can shift the background against which a Gal d 5 reading is interpreted.
• Cooking matters: because Gal d 5 is partly heat-sensitive, a person with isolated Gal d 5 sensitivity may tolerate well-cooked egg yolk while reacting to raw or lightly cooked yolk.

What an Unexpected Result Should Prompt

If your Gal d 5 IgE is positive and you have not been formally evaluated for egg allergy, the next step is a structured workup with an allergist. That usually means whole egg white IgE, ovomucoid (Gal d 1) IgE, a skin prick test, and depending on findings, a basophil activation test or an oral food challenge.

If you have respiratory symptoms around birds or bird-related occupational exposure plus a positive Gal d 5, ask specifically about bird-egg syndrome. The combination changes both diagnosis and the avoidance strategy, since the relevant exposures extend beyond food.

If you already have a known egg allergy and you are seeing Gal d 5 results trend downward across serial tests alongside egg white IgE, that pattern is consistent with the immune system moving toward tolerance. Decisions about reintroducing egg, whether baked or whole, should still be guided by an allergist and ideally confirmed by a supervised challenge rather than by lab values alone.