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Blood Test Tracker

Perennial Rye Grass IgE

Measures IgE antibodies to perennial ryegrass pollen, which shows whether your immune system has become sensitized to this common grass.

AI-verified against cited sources. Awaiting expert reviewAlso called g5, G005LOINC 7369-2

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What it is

This test measures IgE, the antibody type involved in allergic reactions, against pollen from perennial ryegrass (Lolium perenne, ImmunoCAP g5). Ryegrass is a cool-season grass used for lawns, pastures and hay, and it grows across the temperate parts of the world. Its pollen is carried by wind and is a well-known trigger of hay fever in late spring and early summer. Results come in kilounits per liter (kU/L), and many labs also print a class from 0 to 6.

Why it matters

Grass pollen is a leading cause of hay fever, with sneezing, a runny or stuffy nose and itchy eyes, and it can bring on asthma symptoms in people who are sensitive to it. In some places, large amounts of ryegrass pollen in the air around thunderstorms have been linked to sudden asthma attacks in sensitized people, even in some who have not been told they have asthma. A result helps show whether ryegrass may be part of your symptoms, especially if they flare in grass season. Many people have antibodies to grass pollen without symptoms, so 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 ryegrass pollen. This is called sensitization. It is not the same as an allergy, but it can fit with hay fever symptoms during grass season. Higher numbers mean more antibody, not necessarily stronger symptoms. Your clinician can put the result in context.

Common causes

  • Sensitization to grass pollen with no symptoms
  • Seasonal hay fever (allergic rhinitis) or allergic asthma triggered by grass pollen
  • IgE that cross-reacts with related grasses such as Timothy grass or Kentucky bluegrass, so a ryegrass result can reflect a wider grass sensitization
  • IgE to sugar chains on plant proteins (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 grass season
  • Ask whether tests for other grasses would add clarity
  • Ask about ways to reduce pollen exposure, such as staying indoors with the windows closed on high-pollen days
  • If you have asthma, ask whether you need a plan for thunderstorm days in grass season

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, Journal of Allergy and Clinical Immunology, 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 and how much grass pollen you breathe, since ryegrass is most common in temperate regions
  • Related grasses (Timothy, Kentucky bluegrass, orchard grass), which can cause cross-reacting IgE. Bermuda grass cross-reacts less.
  • Antibodies to 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 plant sugar chains (CCD) can give a positive result with little clinical meaning (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 grass season, especially around thunderstorms, 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 grass season?
  • Would testing other grasses help?
  • Should I see an allergist about this?
  • If I have asthma, do I need a plan for thunderstorm days in grass season?
  • My result is in the usual range but I still have symptoms in grass season. What else could be causing them?

Questions people ask

Does this test cover other grasses?

It measures antibodies to ryegrass only. Many grasses share proteins, so people who react to ryegrass often react to Timothy grass or Kentucky bluegrass too. Bermuda grass shares less and needs its own test.

Is perennial ryegrass the same as rye bread?

No. Ryegrass is a lawn and pasture grass. Rye the grain is a different plant with its own test, so this result doesn't answer questions about eating rye.

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 perennial ryegrass (Lolium perenne) pollen extract (ImmunoCAP g5) by fluorescent enzyme immunoassay; ARUP and Labcorp both use the ImmunoCAP system and report the result as LOINC 7369-2. The two dominant allergens are Lol p 1, a beta-expansin with IgE reactivity in more than 90% of ryegrass-sensitized people, and Lol p 5. Lol p 1 tends to affect the upper airway, while Lol p 5 sits on starch granules that can reach the lower airways, especially after thunderstorms (Thermo Fisher). Group 1 allergens within the Pooideae grasses (Lol p 1, Phl p 1, Hol l 1, Pha a 1) share about 90% sequence identity, so IgE to ryegrass often cross-reacts with Timothy grass, Kentucky bluegrass and orchard grass. Cross-reactivity with Bermuda grass (Chloridoideae) and Bahia grass (Panicoideae) is more limited, possibly because Bermuda grass lacks a group 5 allergen. CCD IgE can add a positive extract result of low clinical relevance. NHANES 2005-2006 used a 0.35 kUA/L cutoff and found ryegrass the most common of its 19 allergens, with a positive test in 19.5% of people aged 6 and older. Labs use different cut points: 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. Perennial ryegrass pollen (g5) is distinct from cultivated rye (g12), wild rye (g70) and rye as a food (f5).

LOINC 7369-2 (primary), 112116-9. Specimen: serum.

Sources

  1. G005-IgE Rye Grass, Perennial (test 602543), Labcorp
  2. Sample patient report: G005-IgE Rye Grass, Perennial (test 602543), Labcorp
  3. Allergen, Grass, Perennial Rye Grass (test 0055028), 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: g5 Rye grass, 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. 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. 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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