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Skin prick test is a basic technique to help determine the body's response to allergens to detect allergic drug reactions. This is a simple, accurate and relatively safe test.1. How is the skin prick test done?
Put a drop of drug or allergen solution with suitable concentration on the skin surface, usually on the front of the inner forearm, possibly the skin on the back. Instill a drop of 0.9% NaCl solution 3-4 cm away as a negative control. Instill a positive control histamine solution (concentration of 0.1 mg/mL for histamine base, 0.275 mg/mL for histamine phosphate or 1 mg/mL for histamine dihydrochloride). Use a needle to prick the drops of allergen, yin and yang controls (separate needles are used for each drop). After 15-20 minutes read and evaluate the results. Positive when papule diameter is ≥ 3 mm compared with negative control. Before doing the test, it is necessary to have the emergency equipment ready for anaphylaxis.
Thực hiện test lẩy da đánh giá phản ứng thuốc
| Mức độ | Ký hiệu | Biểu hiện |
| Âm tính | - | Giống như chứng âm tính |
| Nghi ngờ | +/- | Ban sẩn đường kính < 3 mm |
| Dương tính nhẹ | + | Đường kính ban sẩn 3-5 mm, ngứa, xung huyết |
| Dương tính vừa | ++ | Đường kính ban sẩn 6-8 mm, ngứa, xung huyết |
| Dương tính mạnh | +++ | Đường kính ban sẩn 9-12 mm, ngứa, chân giả |
| Dương tính rất mạnh | ++++ | Đường kính trên 12 mm, ngứa nhiều, nhiều chân giả |
2. When should a skin prick test not be performed?
Are suffering from acute allergic disease (rhinitis, urticaria, severe eczema, Quincke's edema, erythema multiforme...). Pregnant women, infants, children younger than 6 months old. Tuberculosis, rheumatism is progressing. Mentally ill patients in the period of exacerbation. Uncontrolled asthma Patient is having lesions in the area of the skin intended to be tested Other acute diseases such as myocardial infarction,... Are taking antihistamines, corticosteroids,...
3. Factors affecting the accuracy of skin prick test
Quality of allergen such as expiry date, preparation technique and storage location Test site (inner forearm, thigh or back...) Techniques eg no bleeding or stinging once or many times.... Age of the patient being tested (reduced response in elderly people, 3-year-old children often have 2 possible cases: Either refractory or overreactive to the allergen) One Some drugs that affect the accuracy of skin prick test include antihistamines, systemic corticosteroids, tricyclic antidepressants. Therefore, antihistamines should be stopped 48-72 hours before the test, systemic corticosteroids 3-5 days before the test, and tricyclic antidepressants for 3 to 10 days.
Những yếu tố nào ảnh hưởng đến kết quả test lẩy da?
At Vinmec International General Hospital, skin prick test was performed for all patients before the first infusion of penicillin and streptomycin antibiotics (unless contraindicated), patients taking Lidocaine and having history of allergy, shock with anesthetics of the amide group or in bronchitis, atopic dermatitis to determine the causative allergen.
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