Prickpuncture tests

Prick-puncture tests are less sensitive and less reproducible, but more specific than intradermal tests.26 The specificity of prick tests and their superior safety profile is the reason why they are recommended by the European Academy of Allergology and Clinical Immunology and the US Joint Council of Allergy, Asthma and Immunology.25

Each antigen is placed upon the skin and introduced into the epidermis. The test is most reliably carried out on the volar aspect of the forearm, though occasionally the patient's back is used if a larger area is needed or the skin of the arm is affected by eczema. Small drops of each allergen extract are placed at least 2 cm apart on the skin. A hypodermic needle is placed at an angle through the drop of liquid and the needle tip is gently inserted to lift the top layer of epidermis, without causing bleeding. A separate needle is used for each allergen extract to reduce the risk of cross-contamination. Positive and negative controls are also used. The negative control identifies the patient with significant dermographism (non-specific skin sensitivity), reducing the chance of false positive reactions. This is commonly allergen diluent, or normal saline. The positive control commonly used is histamine phosphate (1 mg/ml of histamine base).

Other prick-puncture test methods have been developed. These involve the introduction of specific instruments perpendicular to the skin, such as the Morrow Brown standardised needle. This is an attempt to improve repeatability of the test. Opinion is divided as to which method is preferred, although some guidelines do recommend the perpendicular method. 25

Prick-puncture is a safe test; there have been very few reports of systemic reactions, and no fatalities.25

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