What test diagnoses a milk allergy?

Diagnostic Tests for Milk Allergy

Milk allergy diagnosis requires both specific IgE testing (blood test or skin prick test) AND a clinical history of allergic symptoms upon milk exposure, as neither test alone is diagnostic. 1, 2

Primary Diagnostic Tests

1. Specific IgE Testing

• Serum-specific IgE (sIgE) testing:

  • Measures milk-specific IgE antibodies in blood
  • Modern fluorescence enzyme-labeled assays have replaced older RAST tests 1
  • Positive result: ≥0.35 kU/L indicates sensitization 2
  • Higher levels correlate with increased probability of clinical reactivity 1, 2
  • Cutoff values with high predictive value:
    • 2.5 kU/L has 90% positive predictive value 3
    • 5 kU/L has 95% positive predictive value 3

• Skin prick test (SPT):

  • Introduces milk allergen extracts to skin
  • Positive result: wheal size ≥3 mm 4, 3
  • Larger wheal sizes (>8-10 mm) correlate with higher likelihood of clinical allergy 1
  • High negative predictive value (97%) - negative SPT effectively rules out milk allergy 3

2. Oral Food Challenge

• Gold standard for definitive diagnosis 1, 2
• Types:
  • Open challenge: patient and provider know what's being tested
  • Double-blind placebo-controlled food challenge (DBPCFC): most rigorous 1, 2
• Must be performed under medical supervision due to risk of severe reactions 1

Important Diagnostic Principles

Limitations of Testing

• Positive sIgE or SPT alone indicates sensitization, NOT clinical allergy 1, 2
• False positives are common - clinical correlation is essential 2
• Undetectable sIgE levels occasionally occur in patients with true IgE-mediated milk allergy 1, 2
• Results from different laboratories or assay systems may not be comparable 1

Clinical History Elements

• Timing of symptoms after milk ingestion (typically within minutes to 2 hours for IgE-mediated) 1
• Type of symptoms:
  • Skin: hives, eczema flares, facial swelling
  • Gastrointestinal: vomiting, diarrhea, blood in stool
  • Respiratory: wheezing, persistent cough
  • Systemic: irritability, poor feeding 2

Diagnostic Algorithm

1. Initial evaluation:

   • Obtain detailed clinical history of reactions to milk
   • Perform sIgE testing and/or skin prick testing

2. Interpret results:

   • If tests negative + no convincing history: milk allergy unlikely
   • If tests positive + clear history of reactions: milk allergy likely
   • If tests positive + unclear history: proceed to oral food challenge

3. Confirm diagnosis:

   • Oral food challenge under medical supervision when diagnosis remains uncertain
   • Not needed if sIgE levels exceed established predictive cutoffs (≥2.5 kU/L) AND clear clinical history exists 3

Common Pitfalls to Avoid

• Relying solely on IgE testing without clinical correlation 1, 2
• Misinterpreting sensitization as clinical allergy 2
• Failing to recognize that IgE levels may remain positive even after clinical tolerance develops 2
• Not considering non-IgE-mediated milk allergy, which requires different diagnostic approaches 1
• Performing broad panel allergy testing without a history of reaction to foods 1

By following this diagnostic approach, clinicians can accurately diagnose milk allergy, avoid unnecessary dietary restrictions, and implement appropriate management strategies to improve patient outcomes.