Control of Sensitization Patch Test

The technical conditions in which patch tests are performed for the specific reaction of sensitization as well as for the primary toxic reaction must be well determined  

A few hours before the application of the substance, we shear the flanks with an electrical shearing machine, then we shave them very delicately with an electric shaver. Some hours after this we apply the substance with a cotton swab on a surface of about 3 cm, spreading it in the most uniform manner possible. 

As Chase (1954) emphasized, all causes of possible irritation to the surface being tested, must be eliminated in order to avoid misinterpretation scratching of the animals, irritation caused by the method of depilation or by the solvent olive oil may be irritating in 5% of normal animals (Fisher and Cooke, 1958). 

We perform the patch test 8 to 15 days after the end of a sensitization treatment and we interpret the macroscopic reaction generally 12 to 14 hours later, for in sensitized guinea pigs the reaction is best seen at this moment however, it may appear earlier (see citraconic anhydride p. 31). 

The incubation time is shorter if the sensitization is great and the concentration high (Chase, 1954). However, the period of latency cannot in itself be a criterion for the appreciation of the degree of sensitization (Nilzen, 1952). The duration of the macroskopic reaction persists up to approximately 24 hours it varies with the ecze-matogenic substance used. 

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