In a patient with asthma and suspected cow's‑milk allergy, which serum total IgE and specific IgE tests should be ordered?

IgE Testing for Suspected Cow's Milk Allergy in Asthma Patient

Order cow's milk-specific IgE (not total IgE) to identify sensitization to milk proteins, but understand this test alone cannot diagnose clinical allergy and must be correlated with your patient's symptom history. 1

What to Order

Recommended Test

• Order allergen-specific IgE to cow's milk using modern fluorescence-labeled antibody assays (such as ImmunoCAP or equivalent platforms) 1, 2
• The test should specifically target cow's milk proteins, as this directly addresses the suspected allergen 1, 2

Do NOT Order

• Do NOT order total serum IgE - this test lacks specificity for diagnosing food allergy and provides no diagnostic value for identifying milk allergy 1, 2
• The ratio of specific IgE to total IgE offers no advantage over specific IgE alone 1

How to Interpret Results

Negative Result

• **A negative specific IgE (<0.35 kUA/L) effectively rules out IgE-mediated milk allergy** with >95% negative predictive value 3, 2
• If negative, the patient can safely consume milk without further testing 3

Positive Result

• A positive result indicates only sensitization, NOT clinical allergy - many patients have positive tests but tolerate milk without symptoms 1, 2, 4
• Higher specific IgE levels correlate with increased probability of clinical reactivity, though exact predictive thresholds vary 1, 2
• You must correlate positive results with clinical history: does the patient actually develop symptoms (urticaria, angioedema, wheezing, GI symptoms, anaphylaxis) within minutes to hours after milk ingestion? 1, 2

Critical Pitfalls to Avoid

• Never diagnose milk allergy based on laboratory testing alone - up to 50-90% of suspected food allergies based on positive tests are not actual allergies when formally challenged 2
• Different laboratory platforms (ImmunoCAP, Immulite, etc.) yield significantly different measurements for the same sample, so predictive values from one system cannot be applied to another 1, 5, 2
• This patient's asthma is particularly important: coexisting asthma is the most common risk factor for severe allergic reactions to foods, especially if confirmed milk allergy exists 1

When Diagnosis Remains Uncertain

• If the specific IgE is positive but clinical history is unclear or inconsistent, proceed to physician-supervised oral food challenge - this remains the gold standard for definitive diagnosis 1, 2, 4
• Serum testing is particularly useful when skin prick testing cannot be performed due to extensive dermatitis, dermatographism, or inability to discontinue antihistamines 1, 2

Component-Resolved Testing (Optional Advanced Testing)

• If standard cow's milk-specific IgE is equivocal or you need more detailed information, consider component-resolved diagnostics measuring IgE to individual milk proteins: casein, alpha-lactalbumin, beta-lactoglobulin, and bovine serum albumin 6, 7, 8
• Research shows 85% of milk-allergic children have IgE against multiple casein fractions, with highest responses to alpha-s1-casein and beta-casein 8
• However, this level of detail is typically reserved for specialized allergy centers and is not necessary for initial evaluation 2