Why test choice matters in pet allergy

Selecting the right blood test changes how you interpret risk, cross‑reactivity, and what to do next. For pet allergy, clinicians typically start with extract (whole‑dander) specific IgE and add component‑resolved diagnostics only when the clinical picture is unclear or when cross‑sensitization is suspected.

Two ways labs measure IgE to pets

Extract s

IgE (whole dander)

What it is: IgE to crude cat or dog dander extracts (e.g., ImmunoCAP “e1 Cat dander,” “e5 Dog dander”). These are FDA‑cleared analytes widely used in the U.S.
Why it’s useful: High clinical sensitivity; aligns with real‑world exposures; usually enough to guide avoidance and immunotherapy decisions. Thermo Fisher catalog codes confirm e1 (cat) and e5 (dog).
Caveat: Can’t distinguish which molecular allergens drive symptoms; dog extracts vary more than cat in composition and potency across products, which can complicate interpretation.

Component‑resolved s

IgE (molecular allergens)

What it is: IgE to individual proteins (components) from cat/dog. Useful to identify “genuine” sensitization markers (e.g., Fel d 1 for cats) versus cross‑reactive protein families (lipocalins, albumins), and to explain species cross‑reactions (e.g., dog↔cat↔horse lipocalins).
When it helps: Mixed or discordant results, multi‑animal exposure, male‑dog–only symptoms, or when you need to understand risk patterns (e.g., lipocalin polysensitization correlating with asthma severity in some studies).

What the key components mean (cat vs dog)

The components most often discussed in pet allergy and how to read them:

Component	Protein family	Where it comes from	Diagnostic signal	Cross‑reactivity notes
Fel d 1 (cat)	Secretoglobin	Primarily skin/sebaceous and saliva; coats fur via grooming	Marker of genuine cat sensitization; recognized by most cat‑allergic patients	Not strongly cross‑reactive; drives much of cat clinical reactivity
Fel d 4 (cat)	Lipocalin	Saliva, dander, urine	Often co‑sensitizes with Fel d 1; associated with respiratory symptoms	Cross‑reactive with dog Can f 6 and horse Equ c 1 (lipocalins)
Can f 1 (dog)	Lipocalin	Hair/dander/saliva	Major dog marker; childhood Can f 1 sensitization can predict later dog allergy	Lipocalin family; limited cross‑reactivity with some cat lipocalins (e.g., Fel d 7)
Can f 2 (dog)	Lipocalin	Dander	Less frequent; sometimes linked with more severe bronchial inflammation in subsets	Structural homology to other lipocalins; limited patient‑dependent cross‑reactivity
Can f 4 (dog)	Lipocalin	Fur/dander	Frequently detected; associations with asthma reported	Minor cross‑reactivity with Equ c 1 and Fel d 4
Can f 6 (dog)	Lipocalin	Submaxillary gland; dander	Common minor/major allergen; clinically relevant	High sequence identity and IgE cross‑reactivity with Fel d 4 and Equ c 1

Evidence highlights: Fel d 1 is the dominant cat allergen in most patients; Fel d 4–Can f 6–Equ c 1 form a cross‑reactive lipocalin subgroup; lipocalin polysensitization tracks with worse respiratory outcomes in several cohorts.

Lab shorthand you’ll see on reports

Whole‑extract codes: e1 = Cat dander; e5 = Dog dander (ImmunoCAP). These are FDA‑cleared assays that most U.S. labs use to quantify extract sIgE.
Component examples (Thermo Fisher): Fel d 4 = e228; Can f 6 = e230. Many labs offer reflex panels that add components after a positive extract (e.g., Labcorp’s Allergen Profile, Dog with component reflex; hospital catalogs with Can f 1/2/3/4/5/6 reflexing).

When to order components vs rely on extract

Situations where component testing adds value:
You suspect cross‑reactive lipocalins across cat/dog/horse (Fel d 4 ↔ Can f 6 ↔ Equ c 1) and need to counsel on multi‑animal exposure.
Symptoms seem specific to male dogs (consider Can f 5; not required for this article’s core list, but clinically useful).
Discordance (e.g., strong symptoms with weak/negative dog extract) where dog extract variability could obscure a lipocalin driver.
Asthma risk stratification in research/complex cases (lipocalin polysensitization associated with worse lung outcomes in several studies).
Situations where extract sIgE is usually sufficient:
Typical rhinitis/eye symptoms clearly linked to cats/dogs and positive e1/e5.
Deciding on immunotherapy and avoidance in most primary care/telehealth settings, where whole‑dander IgE aligns with the antigens used for treatment.

How extract s

IgE guides treatment at Wyndly

What Wyndly measures: Wyndly’s CLIA‑certified at‑home blood test measures sIgE to 40+ environmental allergens, including cat and dog dander extracts (e1/e5). Results are reviewed by a U.S. board‑certified physician.
How treatment is chosen: If your history and test indicate clinical sensitization to pet dander, your Wyndly doctor may recommend sublingual immunotherapy (SLIT) with pet dander extracts, delivered to your home and monitored virtually.
Helpful information:
Start with the at‑home allergy test.
Learn about pet allergy immunotherapy (SLIT) from Wyndly.
Already have lab results (including components)? Upload them for a physician test review.

Wyndly treats environmental (not food) allergies for patients ages 5+ and offers 24/7 doctor access. Most patients notice improvement between 4 weeks and 6 months and complete therapy in ~3 years.

Quick answers (FAQ)

Do I need component testing to start pet SLIT? Usually no. Positive whole‑dander sIgE (e1/e5) plus symptoms is adequate to begin SLIT; components are reserved for special cases (e.g., suspected cross‑reactivity or male‑dog–only symptoms).

What do the lab codes (e1/e5) mean? They are ImmunoCAP shorthand: e1 = Cat dander extract; e5 = Dog dander extract. Components have their own codes (e.g., Fel d 4 = e228; Can f 6 = e230).

Which cat/dog components explain cross‑reactivity? Lipocalins: Fel d 4 (cat) cross‑reacts with Can f 6 (dog) and Equ c 1 (horse); Fel d 7 can cross‑react with Can f 1.

What does Fel d 1 tell me? Fel d 1 is the dominant, “genuine” marker of cat allergy in most patients; higher Fel d 1 sIgE tracks with more severe respiratory disease in multiple cohorts.

Are dog components linked with worse asthma? Several studies associate sensitization to certain dog lipocalins (e.g., Can f 2/4/6) and polysensitization profiles with higher asthma burden; use clinically with history, not in isolation.

References (open‑access or manufacturer summaries)

Thermo Fisher Scientific. ImmunoCAP allergen list showing e1 (Cat dander) and e5 (Dog dander) FDA‑cleared assays.
Thermo Fisher Allergen Encyclopedia: Fel d 4 lipocalin (component code e228), cross‑reactivity with Can f 6 and Equ c 1.
Thermo Fisher Allergen Encyclopedia: Can f 6 lipocalin (component code e230), cross‑reactivity with Fel d 4 and Equ c 1.
Thermo Fisher Allergen Encyclopedia: Can f 1 lipocalin summary and clinical associations.
Dog & Cat molecular overview (review): Chan & Leung. Dog and Cat Allergies: Current State of Diagnostic Approaches and Challenges. Allergy Asthma Immunol Res. 2018;10(2):97–105.
Structural & cross‑reactivity data: Can f 2 ↔ Fel d 4 (lipocalins). Allergy. 2010;65(6):688–95.
Can f 6 characterization and cross‑reactivity with Fel d 4/Equ c 1. Clin Exp Allergy. 2012;42(4):531–41.
Population data linking lipocalins and clinical outcomes: Open‑access review on furry animal allergens (2025). Clin Rev Allergy Immunol.
Lab reflex example (dog panel with components). Labcorp Test 606659.
Cat major allergen dominance of Fel d 1 (skin/saliva; majority of cat‑allergic patients). Human allergy to cats—review.

Get started with Wyndly

Order the at‑home allergy test.
See how pet SLIT from Wyndly works from home.
Prefer to use prior lab results? Book an existing test review.

Best test for cat and dog allergy: components vs extract sIgE