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Blood Test Tracker

Cat Dander IgE

Measures IgE antibodies to cat dander to show whether your immune system has become sensitized to cat allergens.

AI-verified against cited sources. Awaiting expert reviewAlso called e1, E001LOINC 6833-8

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What it is

This test measures IgE, the antibody type involved in allergic reactions, against cat dander (ImmunoCAP e1). Cat allergens come mainly from saliva and skin, and cats of every breed make them. The main one, Fel d 1, rides on tiny airborne particles, so it turns up in places where no cat has lived. Results come in kilounits per liter (kU/L), and many labs also print a class from 0 to 6.

Why it matters

Cat allergy is one of the most common indoor allergies. It can cause sneezing, itchy eyes, a stuffy nose and, in some people, asthma symptoms. The test shows whether your immune system has IgE to cat allergens, which can help explain symptoms around cats. A positive result without symptoms is common, 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 cat dander. This is called sensitization. It is not the same as an allergy, but it can fit with symptoms around cats. Higher numbers mean more antibody, not necessarily stronger symptoms. Your clinician can put the result in context.

Common causes

  • Sensitization to cat allergens with no symptoms
  • Cat allergy, with hay-fever-like symptoms or asthma around cats or where cats have been
  • IgE that cross-reacts with other furry animals such as dog or horse
  • Cat albumin (Fel d 2) cross-reacting with pork albumin, which is rarely linked to reactions to pork (pork-cat syndrome)

What can help

  • Talk with a clinician or an allergist about whether your symptoms match this result
  • Ask whether a cat component test (such as Fel d 1) would help sort true cat allergy from cross-reaction
  • Ask about practical ways to reduce cat allergen at home, since it can linger in carpets and upholstered furniture for months after a cat leaves

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: ARUP Laboratories, Labcorp, Children's Minnesota Laboratory, Thermo Fisher Scientific (Phadia), American Academy of Pediatrics (Pediatrics).

ImmunoCAP IgE classes (ARUP, Iowa, Children's Minnesota and CUHK; labs differ on which class an exact edge value falls in)

  • Class 0: no significant level detectedbelow 0.1 kU/L
  • Class 0/1: clinical relevance undetermined0.1 to under 0.35 kU/L
  • Class 1: low0.35 to under 0.7 kU/L
  • Class 2: moderate0.7 to under 3.5 kU/L
  • Class 3: high3.5 to under 17.5 kU/L
  • Class 4: very high17.5 to under 50 kU/L
  • Class 5: very high50 to under 100 kU/L
  • Class 6: very high100 and above kU/L

Labcorp class scale (cutoffs differ from the ImmunoCAP scale above; exactly 100.00 is class V)

  • 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 kU/L
  • Class VI: very high100 and above kU/L

What can affect your result

  • How much cat allergen you meet, at home and in places cats have been
  • Sensitization to other furry animals, which can add cross-reacting IgE
  • Having asthma, hay fever or eczema, which often occur together with animal sensitization
  • The lab and test brand, because results from different systems are not directly comparable
  • Antihistamines generally don't interfere with blood IgE tests, unlike skin tests (AAP). MedlinePlus advises telling your provider about everything you take, since some medicines may matter for this test, so ask your clinician before changing any medicine.
  • Assays from different manufacturers aren't equivalent, so compare results only from the same lab and method (AAP).

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 you wheeze or feel chest tightness or shortness of breath around cats, or if allergy symptoms are hard to control, 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 time around cats?
  • Would a cat component test, such as Fel d 1, help tell true cat allergy from cross-reaction?
  • Should I see an allergist about this?
  • My result is in the usual range but I still have symptoms around cats. What should we look at next?

Questions people ask

Can I still react to cats if my result is low or negative?

It is less likely, but a negative result does not completely rule out an allergy, as labs such as ARUP note. If you have symptoms around cats, tell your clinician even if the number is low.

Why can cat allergen bother me where no cat lives?

Cat allergen travels on tiny airborne particles, so it can be found in homes, offices and public places that have never had a cat. It also stays in carpets and upholstered furniture for months after a cat leaves.

What do the class numbers 0 to 6 mean?

The class groups the kU/L number from none detected (class 0) to very high (class 6). Higher classes mean more antibody and a higher chance of a reaction, but not a more severe one. Labcorp's class cutoffs differ from the ones ARUP and many hospital labs use, so compare the kU/L number rather than the class between labs.

Show the science and sources

For clinicians and researchers

Quantitative IgE to cat dander (ImmunoCAP e1) by fluoroenzyme immunoassay; ARUP and Labcorp both use the ImmunoCAP system, which reports about 0.1 to 100 kUA/L. Results from the different FDA-cleared IgE systems are not equivalent (AAP 2012). Thermo Fisher lists Fel d 1 (e94, a uteroglobin) as the major allergen and cat-specific sensitization marker, Fel d 2 (e220, serum albumin) as a minor allergen that cross-reacts with other serum albumins and can be a primary sensitizer in pork-cat syndrome, and Fel d 4 (e228, a lipocalin) as a clinically significant allergen whose IgE without Fel d 1 suggests cross-reactivity with other furry animals (dog Can f 6, horse Equ c 1). It also reports that the risk and severity of respiratory disease rise with the number of pet allergen components a person is sensitized to. Fel d 1 is carried on particles under 5 µm, spreads to places without cats, and can take months to fall after a cat is removed (up to about 20 weeks in Thermo Fisher's summary). If all components are negative and e1 is positive, the person may be sensitized to an untested allergen. A negative test does not rule out clinical allergy (ARUP). ARUP reports 0.10 to 0.34 kU/L as 'clinical relevance undetermined'.

LOINC 6833-8 (primary). Specimen: serum.

Sources

  1. Allergen, Epidermals and Animal Proteins, Cat Dander (test 0055006), ARUP Laboratories
  2. Cat Hair/Dander (test 602454), Labcorp
  3. Sample report 607120, Allergens with Component Reflexes Area 20 (class description table), Labcorp
  4. Allergen (IgE) ImmunoCAP, University of Iowa Hospitals & Clinics, Pathology Handbook
  5. Allergen IgE (laboratory test information), Children's Minnesota Laboratory
  6. Immunoglobulin E (IgE, Allergen-Specific), Serum, Chinese University of Hong Kong, Prince of Wales Hospital ward manual
  7. Your quick guide to using ImmunoCAP Specific IgE testing, Thermo Fisher Scientific (Phadia) (2024)
  8. Allergy Testing in Childhood: Using Allergen-Specific IgE Tests (clinical report), American Academy of Pediatrics (Pediatrics) (2012)
  9. Allergy Blood Tests, MedlinePlus (National Library of Medicine)
  10. ImmunoCAP Specific IgE tests: Cat allergy (testing algorithm), Thermo Fisher Scientific (Phadia) (2025)
  11. Allergen Encyclopedia: Cat (e1), Thermo Fisher Scientific (Phadia)

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

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