Intradermal Reaction

Intradermal reaction, or intracutaneous (from Latin intra- within and cutis- skin), along with cutaneous, subcutaneous, and conjunctival, is used for the following purposes: 1) to detect allergic conditions, i.e., increased sensitivity to a particular substance ('allergen'); 2) for diagnostic purposes in tuberculosis, syphilis, glanders, typhoid fever, gonorrhea, cerebrospinal meningitis, pregnancy, cancer, actinomycosis, pseudotuberculosis, etc.; 3) to determine sensitivity to a given toxin, which indicates the body's susceptibility to the corresponding infection; such are the reactions to diphtheria toxin (Schick reaction) and to scarlatinal toxin (Dick reaction); 4) for titrating antidiphtheric sera according to Romer and for determining the virulence of diphtheria bacilli. Walker and Adkinson, comparing the intradermal reaction with the cutaneous, concluded that the cutaneous method is simpler, requires no special instruments, causes less discomfort to the patient, gives a faster result, and provides fewer opportunities for error due to false reactions, but it is less sensitive than the intradermal. Therefore, the latter method is used only when the cutaneous gives a negative result. The intradermal method, along with the local reaction, more often causes a general reaction due to the easier absorption of the antigen. Special care must be taken when performing the test in cases of extreme sensitivity, especially in persons suffering from bronchial asthma, as well as those sensitive to horse and other sera, egg white, milk, and flower pollen. In such cases, the cutaneous reaction is preferable. If the intradermal reaction is used, very small amounts of antigen are employed, namely: 0.05-0.1 cubic cm of dilution from 1:100 to 1:1,000, starting with the highest dilutions (1:1,000 and more). If the test is performed with bacteria, a bacterial suspension containing 500 million bacteria per 1 cubic cm is used, with 0.05-0.1 cubic cm injected. Technique. The injection is made either on the front-outer surface of the arm or on the flexor surface of the forearm. 0.05-0.1 cubic cm is injected; larger amounts are undesirable as they cause more significant trauma and are painful. The skin is cleansed with alcohol, fixed between the fourth and thumb of the left hand, and the needle is inserted from below upward almost parallel to the skin surface until the eye of the needle is completely in the skin, with the point of the needle being visible through the epidermis. A whitish blister, pierced by hair roots, appears at the injection site. If the antigen solution is prepared with the addition of 0.2-0.3% phenol, a control (injection of physiological salt solution with the same phenol content) is necessary. The injection sites should be at least 3-5 cm apart. Manifestation of allergic reaction: the white blister obtained at the injection site does not dissolve, but instead grows and already after 5-10 minutes reaches several times its original size. With particularly strong allergic reactions, curved processes resembling pseudopodia extend from the periphery of the blister along the lymphatic pathways. Intense redness with skin infiltration appears around the blister, which may involve the entire limb and even spread to the nearest parts of the trunk, with the redness not being continuous toward the periphery but taking the form of a rash, sometimes petechial in nature. The allergic reaction reaches its maximum development after 20-30 minutes, after which it begins to subside, although traces of it are still noticeable after 24 hours (sometimes even after 48 h.). Some experience is necessary to be able to distinguish a weak degree of reaction from traumatic and non-specific reactions. Due to the possibility of severe general phenomena (decline in cardiac activity, edema of the skin and mucous membranes, elevated temperature), no more than 6-8 injections are made at the same time. If severe general phenomena occur, which develop as quickly as the local ones, an excellent effect is obtained by injecting adrenaline diluted 1:1,000, in doses for children of 0.3-0.6 cubic cm and for adults-1.0 cubic cm. In case of heart dilation, intravenous injection of strophanthin in a dose of 0.001 for an adult is also recommended (see also Anaphylaxis).