Contraindications of skin prick test

Skin prick test is a basic method to determine the patient's allergic status to a certain drug. However, not all cases should be performed skin prick test. Cases that are contraindicated to skin prick testing such as acute skin infections, use of antidepressants, antihistamines,...

Skin prick test is a basic method for diagnosing allergic diseases, detecting a small mark on the surface of the skin to see a response after a skin prick. Skin prick test with drug is done by using 1 drop of solution is placed on the surface of the skin, then using a needle to insert the drop of solution through the epidermis and then gently prick. The site of skin prick testing is usually the arm. After 30-60 minutes, the response results on the patient can be read.
Skin prick testing can be performed on most patients, regardless of age. If an immune response is seen resulting in redness, urticaria, or worsening, even anaphylaxis, the patient's hypersensitivity to the tested allergen can be concluded. Specifically:
Suspected positive: maculopapular rash < 3mm in diameter. Mildly positive: maculopapular 3-5mm in diameter, pruritic and congestive. Moderately positive: maculopapular rash with a diameter of 6-8mm, erythema and pruritus. Strong positive: maculopapular 9-12 mm in diameter, prosthetic and pruritic. Very strong positivity: maculopapular rash >12mm in diameter, many prosthetic legs and intense itching. However, it is necessary to make sure that the patient does not have skin diseases, or in some cases can falsify the results. Therefore, skin prick testing is contraindicated in certain cases.

Titration of a skin prick test that uses an intradermal injection of an increased concentration of an allergen to measure the response to an allergic reaction. To prevent a serious allergic reaction in the patient, the test should be performed starting with a very small diluent. After 10 minutes at the injection site, the progression circle was measured, if a 2mm blister appeared on the skin within 10 minutes, it was considered positive. Then continue with a second injection with a higher concentration to determine response. The final result is to determine the concentration of antigens that increase the size of the redness caused by allergies. If in the case of redness develops > 12mm, no further injection is required, this is considered a severe hypersensitivity reaction.
SEE ALSO: Skin test helps detect allergies

Skin prick tests are available at any age. However, in some cases, it can aggravate the condition or give false test results. Therefore, some cases need contraindications to skin prick testing.
3.1. Cases of contraindications to skin prick test In case there is no anaphylactic first aid kit For pregnant women The patient is suffering from some of the following allergic diseases: rhinitis, urticaria, angioedema, asthma, anaphylaxis, ... Other serious diseases that make the body exhausted Inflammation of the skin area, test 3.2. Relative contraindications Patients taking beta-blockers or adrenergic antagonisst Patients taking ACE-inhbitors Patients taking medications that inhibit skin reactions, antihistamines, antidepressants, drugs Preventing gastric secretions Chronic diseases such as cancer, kidney failure,... UV-B irradiation on the test area

In summary, skin prick testing is a basic method to help determine the patient's allergy status. This is a quick and easy diagnostic method. However, in some cases, it can aggravate the patient's condition or distort the results such as the patient has a skin disease, uses antihistamines, antidepressants,...
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 a history of allergy, shock with anesthetics of the amide group or in bronchitis, atopic dermatitis to determine the allergen causing the disease.