What are the indications for allergy retesting during Immunotherapy (IT)?

Indications for Allergy Retesting During Immunotherapy

Routine retesting during ongoing immunotherapy is not indicated and should be avoided unless there is a documented change in environmental exposures or loss of symptom control. 1

Primary Indication: Change in Clinical Circumstances

The most recent guideline evidence establishes a clear, restrictive approach to retesting during active immunotherapy:

• Retesting is only warranted when patients experience loss of symptom control or have documented changes in environmental exposures 1
• Retesting should not be used as a routine assessment tool to measure immunotherapy efficacy, as clinical response (symptom improvement, reduced medication use) is the appropriate outcome measure 1

Specific Situations Requiring Retesting

1. Change in Immunotherapy Extract Formulation

When the allergen extract itself must be changed, retesting becomes necessary:

• Any change in extract constituents (lot number, manufacturer, vaccine type, or component allergens) requires the patient to be retested for specific IgE to appropriate allergens 1
• This includes transitions between standardized and non-standardized extracts, or changes from aqueous to glycerinated preparations 1
• The increased risk of systemic reactions with extract changes is particularly high with non-standardized extracts and allergen mixtures 1

2. Geographic Relocation

• Retesting is indicated when patients move to a new geographic area where the allergen immunotherapy extract contents may no longer be appropriate for local environmental exposures 1
• The new physician must verify that component allergens remain clinically relevant to the patient's current environment 1

3. Loss of Symptom Control During Maintenance

• If a patient on maintenance immunotherapy develops worsening symptoms despite adequate dosing, retesting may identify new clinically relevant sensitizations 1
• This scenario suggests either inadequate treatment of existing allergens or development of new sensitivities 1

What Retesting Does NOT Accomplish

Understanding the limitations of retesting prevents unnecessary procedures:

• Skin test reactivity and serum IgE levels do not reliably correlate with clinical response to immunotherapy 1
• Immunologic changes (decreased skin test reactivity, increased IgG blocking antibodies) occur during successful immunotherapy but do not predict clinical outcomes 1
• The initial increase then decrease in serum-specific IgE during immunotherapy is expected and does not indicate treatment failure 1

Common Pitfalls to Avoid

• Do not retest to "confirm" immunotherapy is working - clinical symptom improvement and reduced medication requirements are the appropriate efficacy measures 1
• Do not use IgG antibody testing to guide immunotherapy decisions - only IgE testing (skin or serum) is appropriate for allergen identification 2
• Do not assume all positive tests require treatment - correlation with clinical history and exposure patterns is essential, as up to 54% of the general population tests positive on skin prick tests without clinical disease 2

Transfer of Care Scenario

When patients transfer between physicians, retesting may be avoided if:

• Complete documentation of the previous immunotherapy schedule and extract contents is available 1
• The previous physician can continue providing the identical extract formulation 1
• The patient has shown significant clinical improvement on the current regimen 1
• If documentation is incomplete or the extract must be reformulated, retesting is mandatory before continuing therapy 1

Algorithm for Decision-Making

Step 1: Is the patient experiencing adequate symptom control on current immunotherapy?

• Yes → No retesting indicated 1
• No → Proceed to Step 2

Step 2: Has there been a change in environmental exposures (new pets, relocation, new occupational exposures)?

• Yes → Retest to identify new clinically relevant allergens 1
• No → Proceed to Step 3

Step 3: Is the immunotherapy extract formulation changing (manufacturer, lot, standardization status)?

• Yes → Retest for specific IgE to guide new extract formulation 1
• No → Optimize current regimen without retesting; consider alternative explanations for symptom breakthrough 1