Kiwi (Act d 5) IgE

If you have reacted to kiwi but your standard allergy panel was confusing or contradictory, this is one of the tests that can sharpen the picture. It measures whether your immune system has built antibodies against a specific kiwi protein, helping separate genuine kiwi allergy from reactions that are actually driven by pollen or latex cross-reactivity.

The result matters because what you do next depends on which type of allergy you actually have. Primary kiwi allergy can produce severe, body-wide reactions and requires strict avoidance. Pollen-related kiwi sensitivity often produces only mild mouth symptoms and may behave very differently in cooked versus raw fruit. This component test is one of several that help you and your clinician tell those apart.

What This Test Actually Measures

The test quantifies IgE (immunoglobulin E, the antibody class your immune system uses for allergic reactions) directed specifically against Act d 5, also known as kiwellin. Kiwellin is one of roughly a dozen identified kiwi proteins (13 are catalogued in green kiwifruit) that can trigger an allergic response. Instead of testing your blood against a whole-fruit kiwi extract (which contains many proteins jumbled together), this test isolates one purified component and asks: has your immune system targeted this exact molecule?

This approach is called component-resolved diagnostics. It is a more granular form of allergy testing than the older whole-extract method, because different kiwi proteins carry different clinical meanings. Some are markers of severe, kiwi-specific allergy. Others mostly reflect cross-reactivity with birch pollen, grasses, or latex, and tend to cause milder symptoms.

Where Act d 5 fits in this hierarchy is not fully settled. Some reviews list kiwellin among the major kiwi allergens, while others classify it as a minor allergen, and one pediatric study placed it in the minor category. This is one reason Act d 5 is best interpreted alongside other components rather than on its own.

How It Performs as a Diagnostic Tool

The strongest evidence on this marker comes from a study of adults with kiwi allergy confirmed by a controlled food challenge, compared against allergic and non-allergic controls. The researchers tested how well different combinations of kiwi components could identify true kiwi allergy.

Source: Bublin et al., 2010 (challenge-confirmed kiwi-allergic adults plus 10 atopic controls; the small control group limits how widely these specificity figures can be generalized).

What this means for you: standard commercial kiwi extract tests detect only a small fraction of real cases. A kiwi-specific component panel that includes Act d 5 raises detection while keeping false alarms relatively low. Adding the pollen-related components Act d 8 and Act d 9 boosts sensitivity but causes specificity to fall sharply, because many people sensitized to birch pollen will test positive without having true kiwi allergy.

Separating Real Kiwi Allergy From Pollen Cross-Reactivity

Many people who think they are allergic to kiwi are actually reacting to a kiwi protein that looks structurally similar to a birch pollen protein their immune system already knows. This produces oral allergy syndrome (itchy mouth, mild lip swelling) that is usually limited and rarely dangerous. Component testing helps you tell whether you fall into this category or into the higher-risk primary-allergy group.

Within the kiwi component family, each protein carries a different signal. A large European study of kiwi-allergic patients across multiple countries (Le et al., 2013) found that sensitization patterns vary geographically and that Act d 1 in particular was independently linked to more severe reactions (odds ratio 3.98, P = 0.003). Act d 8 (the birch-pollen-related protein) and Act d 9 (a profilin) marked milder, pollen-driven disease. Act d 5 sits in the kiwi-specific group, but the severity signal in that study was driven primarily by Act d 1 rather than by Act d 5.

Geographic and Population Patterns

Sensitization to specific kiwi components varies by region. In the European cohort cited above, Act d 1 sensitization was notably high in Iceland (32%) and the severity association with Act d 1 was particularly tied to that population (odds ratio 5.60 for living in Iceland). Act d 8 dominated in western and central Europe, and Act d 9 and Act d 10 were more frequent in southern Europe. This is one reason why a single threshold for any component, including Act d 5, is not universal.

Pediatric data are sparser. A literature review covering kiwi allergy in children (Bringheli et al., 2023) noted that diagnostic performance evidence is mixed and largely driven by Act d 1 and whole-extract testing rather than by Act d 5 alone. A Singaporean pediatric cohort (Mathews et al., 2025) relied on skin testing because component-resolved blood testing was not yet routinely available, which the authors flagged as a gap in pediatric care.

Why Act d 5 Is Best Read Alongside Other Components

A single positive or negative on Act d 5 in isolation does not give you a complete picture. The strongest interpretive signal comes from combining Act d 5 with Act d 1 (the marker most consistently linked to primary, potentially severe kiwi allergy), Act d 8 and Act d 9 (markers of pollen-related, usually milder reactions), and Act d 10 (a lipid transfer protein that, in southern European populations, can be linked to more serious systemic reactions rather than mouth-only symptoms). The pattern of positives and negatives across these proteins tells you more than any single value.

Symptom severity does not correlate cleanly with how high the IgE number is for any one component, including Act d 5. The presence of sensitization to certain proteins matters more than the absolute level. This is one reason to interpret results with a clinician familiar with component-resolved diagnostics rather than in isolation.

When Results Can Be Misleading

A few things can blur the picture from a single reading.

• Sensitization without symptoms: a positive IgE result means your immune system recognizes the protein, but it does not guarantee you will have a clinical reaction if you eat kiwi. Sensitization and allergy are not the same thing.
• Cross-reactive components on the same panel: if your sample is also positive for Act d 8 (the birch-related protein) or Act d 9 (a profilin), those positives can drag down the apparent specificity of any kiwi panel. In the Bublin study, specificity fell from about 90% to roughly 30 to 40% once these highly cross-reactive proteins were factored in.
• Assay differences: the laboratory method (ImmunoCAP, ALEX, ISAC, or other multiplex platforms) and the source of the allergen used (recombinant vs natural, green vs gold kiwi) can shift the result. If you retest, it is best to use the same lab and method.
• Variant panel coverage: Act d 5 is only one of more than a dozen identified kiwi allergens. A negative on Act d 5 does not rule out a clinically meaningful allergy driven by Act d 1, Act d 12, Act d 13, or others not on the panel you ordered.

Tracking Your Trend Over Time

Allergen-specific IgE is a dynamic measurement, not a fixed genetic trait. Levels can drift with age, with avoidance, with new pollen seasons, and with any immunotherapy you may be doing. If you have a baseline value, retesting after a meaningful interval (typically 12 months, or 3 to 6 months if you are actively undergoing immunotherapy or have made major exposure changes) is more informative than a single reading.

Trend direction matters more than any single number. A falling Act d 5 IgE over years, especially if accompanied by tolerance on supervised challenge, suggests the immune memory may be quieting. A rising value, especially if paired with new symptoms, justifies revisiting your management plan. Single readings can fluctuate from one draw to the next without clinical meaning.

Decision Pathway for an Unexpected Result

If your Act d 5 result is out of pattern with how you actually react to kiwi, treat the result as one input rather than a verdict. The following companion steps are worth considering with an allergist:

• Order the full kiwi component panel: Act d 1, Act d 2, Act d 8, Act d 9, and Act d 10 alongside Act d 5 give you the pattern needed to distinguish primary kiwi allergy from pollen-driven or latex-driven cross-reactivity. Act d 1 in particular is the component most consistently tied to severe reactions.
• Add pollen and latex IgE testing: birch (Bet v 1), grass mix, and latex panels help clarify whether your kiwi sensitization is part of a larger cross-reactive profile.
• Consider a skin prick or prick-to-prick test with fresh kiwi: fresh fruit often performs better than commercial extracts because some kiwi proteins degrade quickly. In one study, prick-to-prick testing with fresh kiwi reached about 82% sensitivity and 94% specificity, outperforming extract-based options.
• Discuss a supervised oral food challenge: for ambiguous cases, this remains the most reliable way to know whether your sensitization translates into clinical allergy.

Combinations of findings matter more than any single positive. A positive Act d 1 with a positive Act d 5 and negative pollen-related components points toward primary kiwi allergy that may warrant strict avoidance and an epinephrine auto-injector. A negative Act d 1 and Act d 5 with positive Act d 8 and birch IgE points toward pollen-food syndrome, often manageable with cooked kiwi only and without the same level of risk.