Kiwi (Act d 5) IgE Test · Blood

If you have reacted to kiwi and a standard kiwi allergy test came back uncertain or negative, this test gives you a sharper read. It measures your immune response to a single kiwi protein, Act d 5 (also called kiwellin), rather than the messy mix of proteins in whole kiwi extract.

This is one piece of what allergists call component-resolved diagnostics, a way of identifying which exact molecule in a food is triggering you. Knowing this helps separate a genuine kiwi allergy from a pollen-driven cross-reaction that just happens to flare with kiwi.

What Act d 5 IgE Actually Tells You

Act d 5 IgE (immunoglobulin E) is one of several kiwi component antibodies your blood can be tested for. The full kiwi panel can include Act d 1, Act d 2, Act d 4, Act d 5, Act d 8, Act d 9, Act d 10, and others. Each of these proteins behaves differently in the body and points to a different kind of kiwi sensitivity.

On its own, Act d 5 is not the strongest single marker for kiwi allergy. Its value is in what it adds to a panel. When combined with Act d 1, Act d 2, and Act d 4, the panel reaches about 40% sensitivity (it catches roughly 40 out of 100 confirmed kiwi-allergic people) and 90% specificity (it correctly clears 90 out of 100 people without kiwi allergy). That makes it useful for ruling kiwi allergy in, not for ruling it out.

How It Performs Compared to Standard Kiwi Testing

Standard kiwi IgE testing uses whole-fruit extract. That sounds thorough but the extract is often missing or degraded versions of the very proteins that matter, which is why a normal extract test can quietly miss a real allergy.

Source: Bublin et al., Journal of Allergy and Clinical Immunology, 2010.

What this means for you: adding Act d 5 to a focused kiwi component panel catches some people the basic extract test misses, without flooding the result with false positives from people who only have pollen-related cross-reactivity. If your kiwi extract IgE is negative but you still react to kiwi, components like Act d 5 may be the missing piece.

Reading the Bigger Allergy Picture

Kiwi allergy is not one disease. It splits into roughly two patterns. Some people are primarily allergic to kiwi itself, often with systemic reactions like hives, swelling, or anaphylaxis. Others are sensitive to kiwi only because their body confuses kiwi proteins with pollen or latex proteins, and they usually get milder oral symptoms like itchy lips.

Act d 1 is the marker most strongly linked to genuine, sometimes severe kiwi allergy. Act d 8 (a birch-pollen-like protein) and Act d 9 (a profilin) usually mark milder, pollen-driven cross-reactions. Act d 5 sits in the middle, contributing to specificity when combined with the other primary kiwi components. In one European study of 311 kiwi-allergic patients, the dominant component varied by region: Act d 1 was more common in Iceland, Act d 8 in central and eastern Europe, and Act d 9 and Act d 10 in southern Europe.

What This Test Cannot Tell You

A positive Act d 5 result confirms sensitization. It does not predict how severe your reaction will be. Across the published kiwi component studies, IgE levels to individual components do not reliably correlate with reaction severity. And a negative Act d 5 result does not rule kiwi allergy out, since most kiwi-allergic people react primarily to Act d 1 or other components.

This is a research-grade marker. Standardized clinical cutpoints do not yet exist for Act d 5 specifically. Use it as part of a panel and a clinical history, not as a stand-alone verdict.

Tracking Your Trend

A single allergy IgE result captures one moment. Sensitization can rise or fall over years, especially in children, and after sustained avoidance some people see their levels drift down. Tracking trends matters more than chasing a single number.

A reasonable approach: get a baseline now if you have reacted to kiwi or have a strong family history of food allergy, retest in 12 months if you have been avoiding kiwi or undergoing immunotherapy, and check again any time your symptoms change. If your level shifts meaningfully between tests, that is the signal worth acting on, not the raw number.

What to Do With an Out-of-Pattern Result

If your Act d 5 IgE is positive but your standard kiwi extract test was negative, do not dismiss the discrepancy. Treat the component result as the more reliable signal and talk to an allergist about whether to add other kiwi components (Act d 1, Act d 2, Act d 8, Act d 10) to clarify which type of kiwi allergy you have.

If you are positive for Act d 1 alongside Act d 5, that combination raises the suspicion of primary kiwi allergy and warrants a serious conversation about strict avoidance and carrying epinephrine. If you are positive only for the cross-reactive components (Act d 8, Act d 9), your reactions may be milder and pollen-driven, and your doctor may explore whether cooked kiwi is tolerable. An oral food challenge supervised by an allergist remains the diagnostic gold standard when results and symptoms do not line up.

Who Should Pay Attention

This test is most informative if you have had a reaction to kiwi, if you carry a birch pollen allergy or latex allergy and want to map your cross-reactivity risk, or if a basic kiwi panel was inconclusive. There is no evidence supporting routine screening of people without symptoms for Act d 5 IgE; testing is meant for people with a clinical reason to ask the question.