Sugi (Cry j 1) IgE Test · Blood

If spring in Japan or East Asia leaves you sneezing, congested, and miserable, the question worth answering is not just whether you have allergies but which pollen is actually triggering them. This test pinpoints whether your immune system is reacting specifically to Japanese cedar (Cryptomeria japonica), known locally as sugi, the leading cause of seasonal allergy in Japan.

The result tells you whether your body has built up antibodies against Cry j 1, the main allergen in Japanese cedar pollen. Knowing this changes what you can do about it, from targeted immunotherapy to anticipating which seasons will hit you hardest and which related pollens might also cause trouble.

What This Test Actually Measures

This test measures IgE (immunoglobulin E), a type of antibody your immune system produces when it treats a harmless substance as a threat. Specifically, it detects IgE that targets Cry j 1, the dominant protein in Japanese cedar pollen. When pollen lands on your nose, eyes, or airways, these antibodies trigger the release of chemicals that cause sneezing, itching, congestion, and watery eyes.

Cry j 1 is considered a major allergen because the vast majority of people with cedar pollinosis (the medical name for cedar pollen allergy) react to it. In studies of patients with Japanese cedar pollinosis, over 90% had specific IgE antibodies to both Cry j 1 and the second major cedar allergen, Cry j 2.

How Common Cedar Sensitization Is

Sensitization to Japanese cedar is widespread, especially in Japan, and the numbers climb sharply with age in childhood. In a Tokyo birth cohort, Cry j 1 sensitization rose from about 33% of children at age 5 to roughly 58% by age 9, tracking the rising prevalence of allergic rhinitis in parallel. By adolescence, nearly all young people with pollen allergy show cedar sensitization on component testing.

In a national Japanese pregnancy cohort of nearly 150,000 mothers, about 56% had IgE sensitization to Japanese cedar, making it the most prevalent allergen of any tested. Among hospital workers in Japan, the prevalence of cedar pollen allergic rhinitis has continued climbing over the past decade.

Allergic Rhinitis and Quality of Life

Cedar pollen sensitization is not a harmless lab finding. In a study of 1,476 Japanese 8-year-olds, 68.6% were positive for Japanese cedar pollen IgE, and many had moderate to severe rhinitis symptoms that meaningfully reduced their quality of life. In another cohort of 9-year-olds, children sensitized to Cry j 1 had two to four times higher odds of allergic disease compared with non-sensitized peers, and about three-quarters of sensitized children had clinical rhinitis.

What this means for you: if you live in or travel to Japan during cedar season (typically February through April) and have nasal or eye symptoms, a positive Cry j 1 IgE result is strong evidence that cedar is driving them. That changes which interventions are likely to actually help.

Predicting Who Will Develop Symptoms

One of the more useful insights from research on this marker is that the ratio of cedar-specific IgE to total IgE may matter more than the cedar IgE number alone. In a prospective study of 33 sensitized but asymptomatic adults, those with a higher pre-season ratio were more likely to develop cedar pollinosis during the season. Eight of the 33 went on to develop symptoms, and a marked post-season rise in specific IgE accompanied this transition.

This pattern matters for people who test positive on a routine allergy panel but feel fine. Sensitization on a lab report is not the same as clinical allergy, and tracking the ratio over time gives a more meaningful picture of whether your immune system is heading toward symptomatic disease.

Pollen-Food Allergy Syndrome

Japanese cedar sensitization is linked to pollen-food allergy syndrome, where eating certain raw fruits or vegetables triggers oral itching or swelling because the food contains proteins that resemble cedar pollen proteins. In a Japanese population-based study of 506 adolescents, pollen-food allergy syndrome affected roughly 1 in 10 of the general population, with higher pollen-specific IgE levels and more pollen sensitizations increasing the risk.

Cross-reactivity has been described between cedar pollen proteins and certain plant foods, including specific reactions to capsicum (peppers) through a shared gibberellin-regulated protein family. If you have cedar pollinosis and notice tingling or swelling in your mouth after raw fruits or vegetables, this overlap is the likely explanation.

How Treatment Changes Your Antibody Levels

Cedar IgE is one of the few allergy markers where treatment can paradoxically raise the number on your lab report while making you feel better. In randomized trials of oral immunotherapy using a Cry j 1-galactomannan conjugate, serum cedar-specific IgE actually rose during early treatment, alongside rising protective IgG4 antibodies, while symptoms and medication use went down.

This isn't a 'good number / bad number' marker once you're in treatment; it's a treatment-response indicator. A rising cedar IgE on immunotherapy can reflect a strong, expected immune response rather than worsening disease. Conversely, omalizumab (an anti-IgE biologic drug) reduces free IgE substantially, so a dramatically low result during this treatment reflects the medication's effect, not loss of true sensitization. Without that context, either result could be badly misinterpreted.

Tracking Your Trend Over Time

A single Cry j 1 IgE measurement tells you whether you're sensitized right now, but the trend over years is often more useful than any single value. Specific IgE levels shift across the year (rising after pollen season), respond to treatment, and change in childhood as the immune system matures. If you're starting immunotherapy, undergoing biologic therapy, or watching to see whether sensitization is progressing toward clinical disease, serial testing matters.

A reasonable cadence: get a baseline before cedar season, retest after the season to see how your immune system responded to real-world exposure, and recheck annually thereafter. If you start a cedar-specific treatment, plan a follow-up at 6 to 12 months to track immune changes. Use the same lab and assay each time, because methods differ between platforms and the absolute numbers are not directly comparable across them.

What to Do With an Unexpected Result

A positive Cry j 1 IgE in someone with no symptoms means you're sensitized but not necessarily clinically allergic. The right next step is not panic but pattern recognition. Pair this result with a total IgE measurement to see the ratio, consider testing for related cedar/cypress allergens such as Cry j 2 and Japanese cypress, and watch for symptoms during the next cedar season. If you have symptoms but a low cedar IgE, look at house dust mite, other tree pollens, and grass components, since these often coexist.

If you have moderate to severe symptoms confirmed to be cedar-driven, an allergist can discuss whether sublingual immunotherapy tablets (a guideline-supported treatment in Japan) make sense, and whether you should also be tested for cypress, which often co-triggers symptoms because the same immunotherapy dose works for both. People with oral symptoms after raw fruits or vegetables should be evaluated for pollen-food allergy syndrome.

When Results Can Be Misleading

• Cross-reactive carbohydrate determinants: sugars attached to plant proteins can cause false-positive IgE results on multiplex tests. Specialized inhibition testing can correct for this and improve diagnostic accuracy.
• Anti-IgE biologic therapy: omalizumab substantially reduces measurable free IgE, so a low cedar IgE during this treatment reflects the medication, not your true sensitization status.
• Recent immunotherapy: allergen-specific immunotherapy can transiently raise cedar IgE, particularly in the early months of treatment. A rise during therapy is not the same as worsening disease.
• Sensitization without symptoms: a positive IgE result by itself does not equal clinical allergy. Many sensitized people may not develop symptoms, so interpret the result alongside what your body actually does during cedar season.