Normal Parameters for Milk-Specific IgE
The normal reference range for milk-specific IgE is <0.35 kU/L, which effectively rules out IgE-mediated cow's milk allergy with >95% negative predictive value. 1
Understanding the Reference Range
Values <0.35 kU/L are considered negative and indicate no sensitization to cow's milk proteins, making IgE-mediated allergy highly unlikely. 1
Values ≥0.35 kU/L are considered positive and indicate sensitization to cow's milk, though this does not automatically mean clinical allergy exists. 1, 2
The negative predictive value of <0.35 kU/L exceeds 95%, meaning a result below this threshold reliably excludes IgE-mediated cow's milk allergy in the vast majority of cases. 1
Clinical Interpretation Beyond the Basic Threshold
While 0.35 kU/L separates negative from positive results, higher thresholds provide greater diagnostic certainty for true clinical allergy:
2.5 kU/L provides 90% positive predictive value for confirmed cow's milk allergy in infants, meaning 9 out of 10 children with this level will react to milk challenge. 3
5 kU/L provides 95% positive predictive value for confirmed allergy, and oral food challenges should generally be avoided at or above this level due to high reaction risk. 3
In children ≤24 months, 22 kU/L predicts clinical reactivity with 95% probability, while in children >24 months, this threshold rises to 44.1 kU/L. 4
Age-Specific Considerations
Diagnostic thresholds vary by age because immune responses and tolerance development differ across pediatric age groups:
For infants under 12 months, values between 0.35-2.5 kU/L represent a gray zone where clinical history and supervised challenge are essential for diagnosis. 3, 5
Children under 1 year with milk-specific IgE >3 kU/L have an 82.6% probability of persistent allergy at age 3 years, making this a useful prognostic marker. 6
Critical Pitfalls to Avoid
Never diagnose cow's milk allergy based solely on a positive IgE result (≥0.35 kU/L), as 40-60% of positive results do not correlate with clinical reactivity. 1, 2
Do not assume that undetectable IgE (<0.35 kU/L) excludes all forms of milk allergy, as approximately 23.6% of children have non-IgE-mediated cow's milk allergy that will not be detected by this test. 1
Avoid comparing results across different laboratory platforms (ImmunoCAP, Immulite, etc.), as predictive values and cutoff points are assay-specific and not interchangeable. 1
Clinical history must always guide interpretation—a convincing history of immediate reactions (urticaria, angioedema, vomiting, anaphylaxis within 2 hours of milk ingestion) overrides low IgE values and warrants continued avoidance. 1, 2