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What are indications of Allergy Skin Testing and Specific Immunotherapy?

Allergen Immunotherapy after Allergy - Testing

  • Allergic rhinitis and allergic Br. Asthma
  • Allergic rhinitis and Ch. Sinusitis
  • Rhino conjunctivitis and Rec. Urticaria
  • N.B. Allergy & Atopic dermatitis
  • Atopic Steroid - dependent Complicated Br. Asthma
  • Insect hypersensitivity
  • Non compliance and intolerance with pharmacotherapy in allergic diseases

Diagnostic Allergy Testing

  • Allergic Respiratory Mycosis (e.g. A.B.P.A.)
  • Occupational asthma
  • Rec. cough - wheeze and dyspnea - syndrome
  • Food and drug hypersensitivity
  • Anaphylaxis (Food associated exercise induced)
  • Recurrent skin Urticaria / Rashes and / or Angioedma
  • Contact Dermatitis (Air-borne and Chemical) and Atopic Dermatitis

WHO position paper on Allergen Immunotherapy considers allergen disorders as multi-organ diseases.

Skin Prick Test

This test involves using a small needle to prick and inject a drop of fluid containing a known allergen, just under the surface of the skin. The test is usually carried out on the skin on the inner forearm, although with young children it may be done on the back so they cannot see what is happening.

A positive result to the skin prick test is indicated within minutes. The skin around the area pricked will become red and itchy and after about 20 minutes, the area swells and a raised circle known as ‘weal’ appear. The larger the weal, the more likely that you are allergic to the specific allergen. This blister-like circle will fade within a few hours. If your skin does not react in any way, it indicates a negative result. 40 - 50 allergens may be tested at one time.

Contents of the Skin Prick Test:

  • Consultation with the doctor, involving taking family history - 20 minutes
  • Administration of the test depending on the number of allergens - 30 to 50 minutes
  • Waiting period - 15 minutes to 1 hrs
  • Evaluation as well as advice by the doctor - 20 to 30 minutes

Patch Tests

A Patch Test is a reliable way of determining if you are suffering from Allergic contact dermatitis and the cause for it. Allergic contact dermatitis is an itchy skin condition caused by an allergic reaction to material in contact with the skin. It arises some hours after contact with the responsible material, and settles down over some days, provided the skin is no longer in contact with it. The Patch Test involves applying a number of allergens in small amounts to a small area of the skin on the upper back and then covering it with waterproof hypoallergenic tape. The Patch test is left on the back for two days. When you return after two days, your doctor looks at your back to see which allergen (s) caused the reaction. Patch testing helps to test a range of substances specific to each individual.

Precautions while performing an Allergy Test

It is advised to stop all anti-allergic medication 24 hours prior to the allergy tests if you have high blood pressure, or any heart problems, or diabetes, or are pregnant or breast feeding, please inform your doctor.

Some typical examples of Allergic Contact dermatitis include:

  • Eczema of the wrist underlying a watchstrap, due to contact allergy to Nickel.
  • Hand dermatitis caused by Thiuram, an antioxidant chemical used in the manufacture of Rubber Gloves.
  • Itchy red face due to contact allergy with Kaphon CG, a Preservative in the Moisturizer.

It is important to recognize how you are in contact with the responsible substance, so that whenever possible, you can avoid it.

When to Ask For Specific IgE Testing

  • Diagnosing allergies.
  • Extended investigation of allergies in case of eosinophillc pulmonary infiltration, allergic alveolitis.
  • Allergic broncho-pulmonary aspergillosis (A.B.P.A.)
  • Extended investigation of all allergies parallel to screening for specific IgE as a part of differential diagnosis from parasitic disorders.
  • Illness associated with eosinophilia or fever of unknown origin (drug related fever).
  • Diagnosis of igE myeloma.

What is the Mechanism of Specific Allergen Immunotherapy (SIT)?

Immunotherapy with allergen extract is currently the only available specific treatment of allergic diseases, with the potential to reduce symptoms in the long term. It involves giving gradually increasing doses of the antigen or allergen to the person. As the main target of SIT is to balance the TH-2/ TH-I immune response. So initially the TH-2type cell will be “switched off” by induction of apoptosis, T cell allergy results in development of T cell tolerance. Then in the second step “protective” allergen specific TH-1 dominated immune response seems to develop. Later on there is development of novel effectors / T regulator cells in maintenance phase of SIT.

What is the Clinical efficacy of Allergen Specific Immunotherapy in Allergic rhinitis I Rhino conjunctivitis / Asthma?

W’HO panel guidelines suggest that SIT should be considered in patients with moderate to severe rhinitis uncontrolled by the usual drugs and mild asthma. Meta analysis of controlled trials of SIT done by Abramson’ 1995-97 in adults and Jacobson et al in 1998 in childhood asthma compared in those patients treated with SIT with controlled group (Plecobo) has shown consistently effective therapy for selected patients with rhino - conjunctivitis, rhinitis and asthma, which results in a greater than four- fold decrease in the need for symptomatic treatment and a greater than six-fold decrease in bronchial hyper reactivity. There are 53 double blind placebo controlled (D.B.P.C.) studies since 1980 on the base of diminutions of symptoms / medication by > 30% in actively treated patients. The best results were obtained in grass pollen immunotherapy than weed pollen while magnitude of efficacy was modest in other studies of other pollen, house dust mites, animals and molds.

Omalizumab can serve as a bridge to immunotherapy in severe asthma

Asthma is the most common chronic respiratory disease, affecting up to 10% of adults and 30% of children (JACI, 2011) Allergen immunotherapy was introduced by Leonard Noon 100 years ago and is the only disease-modifying treatment for allergic individuals (Allergy, 2012)

Both allergen immunotherapy & omalizumab (anti-IgE antibody) are used to treat persistent perennial allergic asthma. Allergen immunotherapy can lead to long Lasting Improvement with a typical regimen lasting a set time period of 3-5 years. Because severe asthmatic patients are at greater risk for serious and potentially life threatening reactions with allergen immunotherapy But Combined Use of omalizumab act as a bridge to immunotherapy making immunotherapy more effective and safer in high risk severe asthmatics.

How are allergies treated?

Prevention is the key for individuals suffering from allergy. If you know you have an allergy to something, you should make the effort to avoid or reduce contact with the specific allergen. There are also drugs available which can ease an allergic reaction. The most common drugs used for allergy symptoms are antihistamines and steroids, which come in the form of nasal sprays, creams or tablets, your doctor, will guide you on the same.

Does Alternative medicine (e.g. Herbal / Homeopathy) works for Allergic diseases?

Alternative medicine should always be regarded as an adjunct to conventional treatment not a replacement, herbal medicine are very crude and primitive form of pharmacology. They are the mysterious cocktails of unknown plant chemicals, so possibility of side effects is actually higher with them. Do not fall for the argument “It must be safe people have been taking it for centuries” it has been recorded by meta-analysis of 119 research studies that overall difference between placebo and these herbal / homeopathy medicines is not huge among them while the side effect of Liver damage is the great risk. These medicines may contain steroids and have drug interactions with modern medicines. As these drugs have not undergone full safety trials, means taking a leap in the dark, so modern anti-allergy drugs “The pure is Best” are safe. Now excellent treatment is available. We learn more about Allergy-asthma every year. Newer, more effective and safer drugs are always being developed. As a result, most allergic-asthmatic live normal productive lives, research is continuing and outlook is bright, in the era of recombinant allergen vaccine and gene-therapy.

Why Skin Allergy Testing in diagnosis of allergy diseases?

As skin test give us the information of the end result of the entire sequence of the allergy events from interaction of allergen to skin (first binds to two IgE Antibodies, then Cross-linking with two IgE receptor antibodies & then releasing mediators like histamine etc and their response to end organ.) It means the allergy skin test indicates the clinical sensitivity of the individual following natural exposure of allergen to end organ. It gives us two basic information, the specific form of allergic disease and which allergen is responsible for allergic disease. But the allergenic component of sequence - epitope of allergen is variable for different organ system in a individual .That is why correlation between clinical history and skin test sensitivity is the most important parameter for allergic diagnosis.

While blood-allergen-specific-IgE test detect only specific IgE antibodies, doesn’t give information of clinical sensitivity even if they are significant positive (Class 3, Class4). They indicate high density of IgE on the mast cells or basophils cells. There are many drawbacks which limits the meaning of specific-IgE antibodies due to cross-reactions. The extent of these cross-reaction is much higher than the Cross-reactive-Carbohydrate-Determinants.

During the blood Specific IgE tests, IgE molecules are free. They can bind to all available epitopes. This binding is monovalent & each IgE molecule bounds to one epitope, generates a signals in the specific IgE assay cup. This binding is valid for specific allergen as well as for cross-reacting epitope. But in skin allergy test, once IgE bounds to their cells (mast & basophils), IgE are no longer free to move & they must locally co-operate to lead to a degranulation of mast cells.

Here two adjacent IgE molecules must simultaneously bind to adjacent epitopes on a single allergen molecule; as a result compatible epitope should be on the same side of the allergen, at the right distance from each other etc. This would not matter if the presence of repeated identical epitopes along the allergen is the rule. So adjacent IgE must be different to obtain a degranulation of mast cell. Whatever the level of skin sensitization by the size of the weal, a clinical response eg. positive skin test is thus always more difficult but more specific then a serum IgE reaction.

So, in skin two different but cross reactive IgE molecules must simultaneously bind to the cross reactive allergen. One can easily understand as to why cross-reactions are for more frequent during serum specific IgE assay than in mast cell based reaction (weal size Skin tests) thus compared with allergy skin tests, serum IgE assay lack specificity.

Specific IgE are not recommending as a definite answer for several clinical situation. They provide neither diagnostic not prognostic information. They don’t have sufficient sensitivity for absolute positive prediction of anaphylactic sensitization to vemons, penicillin & other anaphylactogens. But specific IgE may be preferable.

  • Severe dermographism, Ichthyosis or generalized eczema.
  • In long acting anti-Histamines, Tricyclic anti-depressants or other medication that may put the patient at undue risk if they are discontinued.
  • Uncooperative with mental or physical imparameters.
  • The evaluation of cross-reactive between insect venoms.
  • If history of anaphylaxis to allergen like latex/Drugs.
  • Adjunctive Lab tests for disease like ABPA or certain parasitic disease.
  • If allergens are not available in skin tests.

Carefully performed allergy testing is essential for a complete diagnosis & clinical allergist need to be expert on the relative advantage & pitfalls of different allergy testing methods.

Skin prick test are predictors of outcome of challenge tests but decision points for each allergens is variable. If SPT is more than 7.5mm, strongly correlates with the challenge test. Some of the allergens are verified by challenge test as (Higher weal size = Clinical diagnosis.)

  • Seasonal allergens > 32.4mm2
  • Perennial Allergens > 31.2mm2
  • Peanut > 6mm
  • Egg > 7mm
  • Milk > 5mm
  • Wheat flour > 5mm
  • Rye flour > 4.5mm

Among allergy tests -

* Skin Test – First choice diagnostic tools

* Specific IgE – Isolated positive Specific IgE doesn’t constitute the absolute proof of allergy.

* BAT – (Basophil Activation Test )- It analyze and quantify allergen specific in vitro activation of basophil cells is additional test if negative skin test but positive specific IgE due to inhalant allergens, latex, venom, food and drugs.

If we do skin testing aimless, misunderstood it will do more harm in bringing allergy practice into disrepute. So, one must know first medicine of allergic disorders then appreciate the value of skin allergy test.

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