Local anaesthetics skin tests

Skin tests are often useful. They are commonly carried out by intradermal injection, but prick, scratch and patch tests may be used (Aldrete and Johnson 1969, 1970). Incaudo et al. (1978) obtained positive results only in 5 (8%) of the 59 patients they reported. Furthermore, the information gained from the skin test results was of little value since some of these were false positives. We had a similar experience in 18 patients with suspected acute reactions to local anaesthetics. Clearly positive results were obtained in only 2 patients, but further investigations carried out in those 18 patients cast further doubt on the validity of skin tests. These investigations are detailed in Chap. 6. 

In summary, the value of skin tests in suspected reactions to local anaesthetics is limited, and the situation is no different from that with the majority of drugs. Both false negatives and false positives account for their low predictive value. 

Alternative in vivo challenge tests have been proposed, such as the nasal (Eyre and Nally 1971), and conjunctival tests, where local anaesthetics are applied locally to those mucous membranes. The subcutaneous injection of a test dose has been advocated by Incaudo et al. (1978). We cannot see any of these tests as being either convincingly reliable or less risky than the conventional skin tests. The single case of fatal reaction to the instillation of one drop of a local anaesthetic into the con-... 

The leucocyte histamine release test (referred to in greater detail in Chaps. 1-7) is one of the in vitro correlates of immediate allergy which may find useful application in investigating reactions to local anaesthetics. It is of some value in detecting acute reactions, whether they are truly anaphylactic or due to direct (non-immune) histamine release (anaphylactoid). It is also more accurate (quantitative), more reliable and more predictive than skin tests, and above all it is free from risk. 

In three of the patients with reactions to local anaesthetics in whom both the skin and the leucocyte histamine release tests were negative, it was thought that their reaction might have been due to an immune mechanism other than anaphylaxis. The lymphocyte transformation test was carried out in these three patients, but the results were negative. 

Other authors have reported the value of the lymphocyte transformation test. Lehner (1971) reported positive results in four patients with suspected allergy to local anaesthetics, in whom the intradermal skin test was negative. 

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