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Blood Test Tracker

Common Ragweed (Short) IgE

Shows whether your immune system has made IgE antibodies to short ragweed pollen, a common cause of late-summer and fall hay fever.

AI-verified against cited sources. Awaiting expert reviewAlso called w1, W001LOINC 6085-5

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What it is

Ragweed is a weed whose pollen is a common cause of hay fever in late summer and fall, mainly in North America and Europe. This test measures IgE, the type of antibody linked to allergic reactions, that your body has made against short (common) ragweed pollen. Giant and western ragweed have their own tests. Sensitization means your body has made IgE antibodies to a substance. It does not always mean you are allergic.

Why it matters

IgE to ragweed is linked to seasonal hay fever: sneezing, a runny or stuffy nose and itchy eyes, and sometimes asthma symptoms. A result can help show whether ragweed may explain symptoms that flare in late summer and fall, and whether treatments aimed at ragweed are worth discussing. A positive result shows sensitization. It doesn't prove ragweed is behind your symptoms, because it can also reflect cross-reaction with related plants such as mugwort.

If it’s high

A result above your lab's usual range means your body has made IgE antibodies to ragweed pollen. Many people with this result have seasonal symptoms, but some don't. The number doesn't tell how bad your symptoms will be.

Common causes

  • An allergy-prone immune system (atopy), which often comes with other pollen allergies
  • Breathing ragweed pollen where ragweed grows, mainly in late summer and fall
  • Cross-reaction with related plants such as mugwort and sunflower, which can make a ragweed result positive
  • IgE to sugar groups that many plant proteins share, which can cause positives with little clinical meaning
  • A recent pollen season, since ragweed IgE can rise afterward

What can help

  • Talk with your clinician about how your symptoms line up with ragweed season
  • Check local pollen forecasts and think about limiting time outdoors on high-pollen days
  • Ask whether an allergy specialist could go over treatment options aimed at ragweed

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 0–0.1 kU/L. Source: Thermo Fisher Scientific, ARUP Laboratories, Labcorp, Quest Diagnostics, Thermo Fisher Scientific (Phadia), Journal of Allergy and Clinical Immunology, NIAID / Journal of Allergy and Clinical Immunology, World Allergy Organization Journal, Journal of Asthma and Allergy, Children's Minnesota.

ImmunoCAP class scale as printed by Quest and ARUP (cut points differ by about 0.01 between labs)

  • Class 0: absent or undetectablebelow 0.1 kU/L
  • Class 0/1: very low level, relevance uncertain0.1 to under 0.35 kU/L
  • Class 1: low level0.35 to under 0.7 kU/L
  • Class 2: moderate level0.7 to under 3.5 kU/L
  • Class 3: high level3.5 to under 17.5 kU/L
  • Class 4: very high level17.5 to under 50 kU/L
  • Class 5: very high level50 to under 100.01 kU/L
  • Class 6: very high level100.01 and above kU/L

Labcorp class scale (ImmunoCAP, as printed on Labcorp reports)

  • Class 0: negativebelow 0.1 kU/L
  • Class 0/I: equivocal or low0.1 to under 0.32 kU/L
  • Class I: low0.32 to under 0.56 kU/L
  • Class II: moderate0.56 to under 1.41 kU/L
  • Class III: high1.41 to under 3.91 kU/L
  • Class IV: very high3.91 to under 19.01 kU/L
  • Class V: very high19.01 to under 100.01 kU/L
  • Class VI: very high100.01 and above kU/L

What can affect your result

  • Season: ragweed IgE can rise after pollen season; in one older US study, levels peaked between mid-September and mid-October
  • Cross-reaction with mugwort, sunflower and other plants in the daisy family
  • Where you live: sensitization to ragweed is more common in North America and Europe
  • Lab method: results from different labs or assay systems may not be comparable
  • Medicines: antihistamines do not change this blood test, unlike skin prick testing
  • Very high total IgE can produce weak, nonspecific positive results.
  • Different assay systems give different numbers for the same blood sample, so compare results from the same lab and method.
  • Some labs reject samples that are hemolyzed (red cells broken), jaundiced (icteric) or lipemic (very fatty).

Antibody levels usually change slowly, over months to years, although ragweed IgE can rise after a pollen season.

When to talk to a clinician

Talk with a clinician if hay fever symptoms in late summer or fall are hard to control, or if you have cough, wheeze or chest tightness. Call your local emergency number for severe trouble breathing.

Questions you could ask

  • Does my result fit what I notice at different times of year?
  • Do my symptoms follow ragweed season?
  • Could this result be cross-reaction with mugwort or another plant?
  • Would a component test or a visit with an allergy specialist help?
  • Are there treatment options aimed at ragweed that are worth discussing for me?

Questions people ask

Why does my ragweed result change from one test to the next?

Ragweed IgE can rise after pollen season, and different labs use slightly different methods. In one older US study, levels peaked between mid-September and mid-October. To compare results fairly, use the same lab and think about the time of year each test was taken.

Can I test positive for ragweed if I've never had ragweed symptoms?

Yes. IgE can come from cross-reaction with mugwort, sunflower and related plants, or from sugar groups that many plants share. A component test, such as Amb a 1, can help your clinician tell the difference.

Does a positive result mean I have ragweed hay fever?

Not by itself. The result shows sensitization. Your clinician looks at it together with when your symptoms happen and where you live.

Show the science and sources

Units

  • 1 kU/L = 1 kU/L
  • 1 kU/L = 1 UA/mL

For clinicians and researchers

ImmunoCAP w1 measures IgE to a short ragweed (Ambrosia artemisiifolia) pollen extract, with a manufacturer range of 0.1 to 100 kUA/L (above 100 is printed as >100). Amb a 1, a pectate lyase, is the major allergen, with IgE reported in about 90% to 95% of ragweed-allergic people, and Amb a 11 is a second major allergen. Amb a 4 (defensin-like) and Amb a 8 (profilin) are minor allergens that share structure with the mugwort allergens Art v 1 and Art v 4, and IgE to cross-reactive carbohydrate determinants can give a positive extract result without true ragweed sensitization. Component testing (Amb a 1, Amb a 4) or mugwort testing can help separate true ragweed sensitization from cross-reaction, especially where mugwort pollen is common. Exposure boosts specific IgE: in older RAST-era studies, ragweed-specific IgE rose with the pollen season. ARUP labels 0.10 to 0.34 kU/L as clinical relevance undetermined, while other labs call it equivocal or very low. The class tables differ slightly between labs, so use the class your own report prints.

LOINC 6085-5 (primary), 112156-5. Specimen: serum.

Sources

  1. Allergens, Weed Profile (test 0055110), ARUP Laboratories
  2. Allergens, Inhalants, Comprehensive Profile IgE (test 0055312), ARUP Laboratories
  3. Allergen Profile With Component Reflexes, Respiratory, Area 2 (test 607111), Labcorp
  4. Sample patient report: Allergens with Component Reflex, Area 20 (test 607120), Labcorp (2021)
  5. ImmunoCAP Specific IgE Blood Test: Allergy Test List (interpretation table and test codes), Quest Diagnostics (2017)
  6. ImmunoCAP Specific IgE blood test results: Interpretation (respiratory results interpretation guide), Thermo Fisher Scientific (Phadia) (2023)
  7. ImmunoCAP Weed Pollen Allergens (Thermo Fisher product page; lists w1 common ragweed; measuring range 0.1 to 100 kUA/L), Thermo Fisher Scientific
  8. ImmunoCAP allergy: Change to Reference Interval Interpretation, UR Medicine Labs, University of Rochester Medical Center (2022)
  9. Prevalence of allergic sensitization in the United States: results from the National Health and Nutrition Examination Survey (NHANES) 2005-2006, Journal of Allergy and Clinical Immunology (2014)
  10. Guidelines for the Diagnosis and Management of Food Allergy in the United States: Report of the NIAID-Sponsored Expert Panel, NIAID / Journal of Allergy and Clinical Immunology (2010)
  11. IgE allergy diagnostics and other relevant tests in allergy, a World Allergy Organization position paper, World Allergy Organization Journal (2020)
  12. Global Ragweed Allergy: Molecular Allergens and Integrated Control Strategies, Journal of Asthma and Allergy (2025)
  13. Maximal rise in IgE antibody following ragweed pollination season, Journal of Allergy and Clinical Immunology (1975)
  14. Allergen IgE (laboratory test manual entry; class table and reporting rules), Children's Minnesota (2018)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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