Drug allergy laboratory findings

Drug allergy is primarily a clinical diagnosis based on the patient history, and a thorough 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.

• 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.
• Complete blood count – a complete blood count (CBC) is useful in ruling out hemolytic type II drug reactions, such as hemolytic anemia, thrombocytopenia or neutropenia.
• Coombs test– the indirect and direct Coomb’s test is used to determine the presence of antibodies on red cell membranes. This test can also be useful in confirming hemolytic anemia. ^[1]
• Basophil activation test- this test quantifies the activation of basophils using flow cytometry. Basophils are implicated in the development of both immune and non-immune mediated drug reactions. Some studies have shown that this test is useful in evaluating allergy towards beta-lactam antibiotics, muscle relaxants, and NSAIDS, however further studies are needed before this type of testing is widely accepted as a diagnostic tool. ^[2]

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