Bos d 8 casein (milk) IgE

Measures IgE antibodies to casein, a main protein in cow's milk that holds up to heat, to show whether your immune system has become sensitized to it.

AI-verified against cited sources. Awaiting expert reviewAlso called f78, F078, Bos d 8LOINC 6062-4

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Your Casein IgE result

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What it is

This test measures IgE, the antibody type involved in allergic reactions, against casein, also called Bos d 8 (ImmunoCAP f78). Casein is one of the main proteins in cow's milk and in dairy foods such as cheese and yogurt. Unlike some other milk proteins, it holds up to heat and digestion. Results come in kilounits per liter (kU/L), and many labs also print a class from 0 to 6. Labs often run it after a whole-milk IgE test.

Why it matters

Cow's milk allergy is common in young children, and many children outgrow it. Because casein survives heating, higher casein IgE levels are linked in studies to reactions to baked milk and to milk allergy that lasts longer. Low or undetectable levels can go with tolerating baked milk, but only a clinician can decide that, often with a supervised food challenge.

If it’s high

A level above the 'none detected' range means the lab found IgE antibodies to casein. This is called sensitization. It is not the same as an allergy, and the number cannot tell you how severe a reaction would be. Higher levels do make a reaction to milk more likely, and they are linked to a lower chance of tolerating baked milk. Your clinician can put the result in context.

Common causes

Sensitization to milk with no reaction when milk is eaten
Cow's milk allergy, which is most common in infants and young children

What can help

Talk with an allergist about what this result means for you or your child, including baked milk and regular milk
Ask whether the other milk proteins (Bos d 4 and Bos d 5) or a supervised food challenge would add clarity
Ask your clinician before adding milk products to the diet or removing them because of a number

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).

Adults (this one applies)0–0.09 kU/L
Sources: 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

Age: milk allergy is most common in young children, and some outgrow it
Sensitization to the other milk proteins (Bos d 4 and Bos d 5), which a clinician reads together with casein
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 trouble breathing, swelling of the lips, tongue or throat, repeated vomiting, dizziness or fainting after milk or dairy. Talk with a clinician before giving baked or regular milk to a child with a known milk allergy, even if this result is low.

Questions you could ask

Which lab method was used, and should I use the same lab for future results?
What does this result mean for baked milk and for regular milk?
Would testing the other milk proteins or a supervised food challenge help?
How often should this be rechecked as my child grows?
Does a low casein level mean we should talk about a supervised baked-milk challenge?

Questions people ask

Does a low casein result mean baked milk is safe?

Not on its own. In one study, every child with undetectable casein IgE tolerated baked milk, but one study cannot decide for an individual child. Supervised food challenges are often used to be sure, so do not try baked milk at home because of a number.

Why test casein if I already had a milk IgE test?

Milk has several proteins that act differently. Casein stays active after heating, while the whey proteins (Bos d 4 and Bos d 5) mostly break down when milk is fully baked. Looking at them separately can help your clinician judge the risk from baked and regular milk.

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 nBos d 8 (casein, ImmunoCAP f78) by fluoroenzyme immunoassay; ARUP and Labcorp both use the ImmunoCAP system. Thermo Fisher describes casein as heat and digestion stable and as a marker of persistent milk allergy, with risk of reactions to both raw and cooked milk. In 225 milk-allergic children from two cohorts evaluated for baked-milk tolerance (UniCAP assay), casein IgE predicted baked-milk reactivity better than whole-milk or beta-lactoglobulin IgE. All 25 children with undetectable casein IgE tolerated baked milk. The 95%-specificity cutoff was 20.2 kUA/L (above it, a baked-milk challenge was unlikely to be passed), the 95%-sensitivity cutoff was about 0.94 kUA/L (below it, a very low risk of reacting to baked milk), and the best single cutoff was 4.95 kUA/L (Caubet 2013). Those cutoffs come from one pediatric cohort and one assay generation, so they are not validated thresholds for every lab, age or population. Higher sIgE reflects the likelihood of a reaction, not its severity (AAP 2012). Labcorp's allergen profiles add casein as a reflex when milk IgE is 0.35 kU/L or higher. Thermo Fisher suggests reassessing milk-allergic children at regular intervals for spontaneous tolerance. ARUP reports 0.10 to 0.34 kU/L as 'clinical relevance undetermined'.

LOINC 6062-4 (primary), 112964-2. Specimen: serum.

Sources

Allergen, Food, Casein (test 0055081), ARUP Laboratories
Casein (test 602554), Labcorp
Allergen Profile, Milk, IgE With Component Reflexes (test 603927), Labcorp
Sample report 607120, Allergens with Component Reflexes Area 20 (class description table), Labcorp
Allergen (IgE) ImmunoCAP, University of Iowa Hospitals & Clinics, Pathology Handbook
Allergen IgE (laboratory test information), Children's Minnesota Laboratory
Immunoglobulin E (IgE, Allergen-Specific), Serum, Chinese University of Hong Kong, Prince of Wales Hospital ward manual
Your quick guide to using ImmunoCAP Specific IgE testing, Thermo Fisher Scientific (Phadia) (2024)
Allergy Testing in Childhood: Using Allergen-Specific IgE Tests (clinical report), American Academy of Pediatrics (Pediatrics) (2012)
Allergy Blood Tests, MedlinePlus (National Library of Medicine)
ImmunoCAP Specific IgE tests: Cow's milk allergy (testing algorithm), Thermo Fisher Scientific (Phadia) (2025)
ImmunoCAP Specific IgE: Milk Allergen Components (interpretation guide), Thermo Fisher Scientific (Phadia) (2022)
Utility of casein-specific IgE levels in predicting reactivity to baked milk, Journal of Allergy and Clinical Immunology (2013)

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