Drug allergy laboratory findings: Difference between revisions
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*Intradermal tests – these tests involve the injection of a small amount of allergen under the skin, into the dermis. It carries a slightly higher risk of adverse allergic reactions when compared to skin testing, but otherwise tests for the same compounds, also leads to the diagnosis of IgE mediated hypersensitivity reactions, and is also useful in ruling out a penicillin allergy. | *Intradermal tests – these tests involve the injection of a small amount of allergen under the skin, into the dermis. It carries a slightly higher risk of adverse allergic reactions when compared to skin testing, but otherwise tests for the same compounds, also leads to the diagnosis of IgE mediated hypersensitivity reactions, and is also useful in ruling out a penicillin allergy. | ||
* [[In-vitro]] tests for immediate drug reactions are available, but are largely considered investigational. | * [[In-vitro]] tests for immediate drug reactions are available, but are largely considered investigational. | ||
*Patch testing | *Patch testing – this type of testing is useful for the diagnosis of various delayed type IV [[cutaneous]] reactions such as [[exanthemata]], acute generalized exanthematous pustulosis, and flexular exanthema. It involves placing an aluminum disc containing allergens mixed with petrolatum on a patient’s back for 48 hours. The patient is then assessed for any reactions that may have occurred. This type of testing is not helpful to the diagnosis of [[Stevens-Johnson syndrome]] or [[toxic epidermal necrolysis]] and is contraindicated in anyone with a history of these conditions. | ||
* [[Intradermal]] testing with delayed readout is more sensitive than a patch test, and involves [[injection]] of a small amount of the allergen dissolved in water, under the skin. A prick test should be done beforehand, and the concentration used should be non-irritating. | * [[Intradermal]] testing with delayed readout is more sensitive than a patch test, and involves [[injection]] of a small amount of the allergen dissolved in water, under the skin. A prick test should be done beforehand, and the concentration used should be non-irritating. | ||
*[[Skin biopsy]] may be useful to distinguish between Stevens-johnson syndrome and toxic epidermal necrolysis, and also to rule out other conditions on the differential diagnosis list. | *[[Skin biopsy]] may be useful to distinguish between Stevens-johnson syndrome and toxic epidermal necrolysis, and also to rule out other conditions on the differential diagnosis list. | ||
Revision as of 19:27, 20 August 2012
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Charmaine Patel, M.D. [2]
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Drug Allergy |
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Overview
Drug allergy and its associated conditions is primarily a clinical diagnosis based on the patient history, and through physical exam. Certain laboratory findings may be seen during the acute phase of the reaction, but are not always specific. Skin testing and biopsies can be performed when there is not a clear diagnosis.
Laboratory Findings
- Erythrocyte sedimentation rate (ESR) may be increased.
- White blood cell (WBC) may be increased.
- Urine eosinophils may be increased, especially in cases of allergic interstitial nephritis.
- Blood eosinophils may be increased, especially in cases of drug induced TEN.
- Liver function tests (LFT)'s may be increased.
- Elevations in tryptase may be seen detected in serum or plasma within several hours after an acute allergic event, and is consistent with anaphylaxis.
- Histamine levels may be elevated after an acute reaction, but is unreliable for diagnosis.
Other Tests
- Skin testing- skin prick testing (SPT) pricks the skin with a tiny amount of the suspected allergen, and leads to the diagnosis of IgE mediated type I hypersensitivity reactions. These tests are standardized for penicillin, and are also useful for local anesthetics, muscle relaxants. These tests are also very sensitive for high-molecular-weight protein substances such as insulin and monoclonal antibodies. A negative test is useful for ruling out a penicillin allergy, however with other tests (except for with high-molecular-weight proteins), a negative test is not always useful for ruling out the presence of serum specific IgE.
- Intradermal tests – these tests involve the injection of a small amount of allergen under the skin, into the dermis. It carries a slightly higher risk of adverse allergic reactions when compared to skin testing, but otherwise tests for the same compounds, also leads to the diagnosis of IgE mediated hypersensitivity reactions, and is also useful in ruling out a penicillin allergy.
- In-vitro tests for immediate drug reactions are available, but are largely considered investigational.
- Patch testing – this type of testing is useful for the diagnosis of various delayed type IV cutaneous reactions such as exanthemata, acute generalized exanthematous pustulosis, and flexular exanthema. It involves placing an aluminum disc containing allergens mixed with petrolatum on a patient’s back for 48 hours. The patient is then assessed for any reactions that may have occurred. This type of testing is not helpful to the diagnosis of Stevens-Johnson syndrome or toxic epidermal necrolysis and is contraindicated in anyone with a history of these conditions.
- Intradermal testing with delayed readout is more sensitive than a patch test, and involves injection of a small amount of the allergen dissolved in water, under the skin. A prick test should be done beforehand, and the concentration used should be non-irritating.
- Skin biopsy may be useful to distinguish between Stevens-johnson syndrome and toxic epidermal necrolysis, and also to rule out other conditions on the differential diagnosis list.