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Blood Test Tracker

Rough pigweed IgE

Measures IgE antibodies to pigweed pollen, which shows whether your immune system has become sensitized to this late-summer weed.

AI-verified against cited sources. Awaiting expert reviewAlso called w14, W014LOINC 7604-2

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What it is

This test measures IgE, the antibody type involved in allergic reactions, against pollen from rough pigweed (Amaranthus retroflexus, ImmunoCAP w14). It is also called common pigweed or redroot pigweed. Pigweed is a weed that grows in farm fields, pastures and bare ground in many parts of the world, and it makes a lot of wind-carried pollen. Its season usually runs from about August to October, though this varies by climate. Results come in kilounits per liter (kU/L), and many labs also print a class from 0 to 6.

Why it matters

Weed pollen can cause hay fever, with sneezing, itching, a runny or stuffy nose and itchy eyes, and it can add to asthma symptoms in people who are sensitive to it. A result helps show whether pigweed may be part of your symptoms, especially if they flare in late summer and fall. Many people have antibodies to pollen without symptoms, and related weeds share proteins, so results can overlap. Your history matters as much as the number.

If it’s high

A level above the 'none detected' range means the lab found IgE antibodies to pigweed pollen. This is called sensitization. It is not the same as an allergy, but it can fit with hay fever symptoms during weed season. Higher numbers mean more antibody, not necessarily stronger symptoms. Your clinician can put the result in context.

Common causes

  • Sensitization to weed pollen with no symptoms
  • Seasonal hay fever (allergic rhinitis) or allergic asthma triggered by weed pollen in late summer and fall
  • IgE that cross-reacts with related weeds such as lamb's quarters, Russian thistle and kochia (burning bush), so a pigweed result can reflect a wider weed sensitization
  • IgE to widely shared pollen proteins or plant sugar chains (called CCD), which can give a positive test with little effect in real life
  • A very low result of 0.10 to 0.34 kU/L, which some labs treat as uncertain

What can help

  • Talk with a clinician or an allergist about whether your symptoms follow late-summer weed season
  • Ask whether tests for other weed pollens, such as ragweed, lamb's quarters or Russian thistle, would add clarity
  • Ask about ways to reduce pollen exposure, such as staying indoors with the windows closed on high-pollen days

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: 0–0.09 kU/L. Source: Labcorp, ARUP Laboratories, Quest Diagnostics, Thermo Fisher Scientific (Phadia), World Allergy Organization Journal, Allergo Journal International, PLoS ONE, MedlinePlus (National Library of Medicine).

ImmunoCAP class scale as printed by Quest and ARUP (labs differ on which class an exact edge value falls in)

  • 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

  • Where you live: pigweed is common on farmland and pastures, and how often people are sensitized varies by region
  • Related weeds (lamb's quarters, Russian thistle, kochia), which can cause cross-reacting IgE
  • Shared pollen proteins (profilin, polcalcin) and plant sugar chains (CCD), which can add a positive result with little clinical meaning
  • The lab and test brand, because results from different systems are not directly comparable
  • IgE to widely shared pollen proteins (profilin, polcalcin) or plant sugar chains (CCD) can give a positive extract result with little clinical meaning (Allergo J Int 2014; PLoS One 2011).
  • Results from different labs and test brands are not directly comparable, so compare results from the same lab and method (WAO 2020).
  • Labs may reject samples that are hemolyzed (red cells broken), jaundiced (icteric) or lipemic (very fatty). ARUP lists all three as unacceptable.
  • MedlinePlus notes that some medicines, such as antihistamines, may matter before an allergy blood test. Tell your clinician about everything you take and ask them what applies to you.

Slow. IgE levels usually shift over months to years, not weeks.

When to talk to a clinician

Get urgent medical help for severe trouble breathing or swelling of the face or throat. Otherwise, talk with a clinician if hay fever is hard to control, or if you notice wheeze, chest tightness or shortness of breath in weed season, even if this result is in the usual range.

Questions you could ask

  • Which lab method was used, and should I use the same lab for future results?
  • Do my symptoms line up with late-summer and fall weed season?
  • Would testing other weeds, such as ragweed or lamb's quarters, help?
  • Should I see an allergist about this?
  • My result is in the usual range but I still have symptoms in weed season. What else could be causing them?

Questions people ask

Why do some labs say common pigweed and others say rough pigweed?

They are the same plant, Amaranthus retroflexus, which is also called redroot pigweed. ImmunoCAP w14 is the code for it. Quest prints rough pigweed, and Labcorp prints common pigweed.

Does this test cover other weeds?

It measures antibodies to pigweed only. Pigweed shares proteins with related weeds such as lamb's quarters, Russian thistle and kochia, so people who react to one may react to others, but each weed needs its own test.

What does a result of 0.10 to 0.34 mean?

It is a very low level of antibody. Labs describe it as equivocal or of undetermined clinical relevance, and ARUP says results in this range are intended for specialist use. Your clinician can tell you whether it matters for you.

Show the science and sources

Units

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

For clinicians and researchers

Quantitative IgE to a pigweed (Amaranthus retroflexus) pollen extract (ImmunoCAP w14) by fluorescent enzyme immunoassay. Quest names the allergen rough pigweed, Labcorp and Thermo Fisher call it common pigweed, and ARUP lists rough, common and redroot pigweed as aliases of the same test; Labcorp and ARUP both report it as LOINC 7604-2. Ama r 1 (an Ole e 1-like protein) and Ama r 2 (a profilin) are the pigweed allergens listed by WHO/IUIS, and a polcalcin (Ama r 3) has been described. Profilins and polcalcins are cross-reactive pan-allergens that give positive results in extract-based tests while being of minor clinical relevance in most patients, and CCD IgE adds further positives of low relevance (Allergo J Int 2014; PLoS One 2011). Thermo Fisher describes extensive IgE cross-reactivity between pigweed and lamb's quarters (Chenopodium album), Russian thistle (Salsola) and kochia, and with some unrelated plants such as mesquite and needle bush. WAO 2020 lists Amaranthus (pigweeds) and the goosefoot-family genera Chenopodium, Salsola and Kochia in its table of cross-reacting weed pollen groups. ARUP's regional respiratory panels use 0.34 kU/L or lower as the reference interval and call 0.10 to 0.34 kU/L 'clinical relevance undetermined', while Labcorp prints a class 0 result as under 0.10 kU/L. Results from different assay systems are not equivalent.

LOINC 7604-2 (primary), 112243-1. Specimen: serum.

Sources

  1. W014-IgE Pigweed, Common (test 602484), Labcorp
  2. Sample patient report: W014-IgE Pigweed, Common (test 602484), Labcorp
  3. Allergen, Weed, Pigweed (test 0055025), ARUP Laboratories
  4. Allergen, Region 12 Respiratory Panel IgE, Arid Southwest (S. AZ, S.E. CA) (test 3001722), ARUP Laboratories
  5. ImmunoCAP Specific IgE Blood Test: Allergy Test List (interpretation table and test codes), Quest Diagnostics (2017)
  6. Your quick guide to using ImmunoCAP Specific IgE testing, Thermo Fisher Scientific (Phadia)
  7. Allergen Encyclopedia: w14 Common Pigweed, Thermo Fisher Scientific (Phadia)
  8. IgE allergy diagnostics and other relevant tests in allergy, a World Allergy Organization position paper, World Allergy Organization Journal (2020)
  9. Marker allergens of weed pollen: basic considerations and diagnostic benefits in the clinical routine: Part 16 of the Series Molecular Allergology, Allergo Journal International (2014)
  10. Reduction of Cross-Reactive Carbohydrate Determinants in Plant Foodstuff: Elucidation of Clinical Relevance and Implications for Allergy Diagnosis, PLoS ONE (2011)
  11. Allergy Blood Test, MedlinePlus (National Library of Medicine)

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

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