nativ = angeboren, natürlich, unverändert, nicht denaturiert
http://www.tk-online.de/rochelexikon/

Bei Nahrungsmittelallergien wird er zudem häufig mit dem „nativen“ (=echten) Nahrungsmittel durchgeführt. (also z.B. mit der Säuglingsnahrung des Kindes)
http://www.allergiezentrum-ibiza.de/de/allergie_allgemeinete...

In einer Scratchtestung wurde ebenfalls das native Material getestet.
The scratch test generated strongly positive reactions against native tube material.
http://www.springerlink.com/content/59jutkv90b4fcxj0/


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Note added at 3 hrs (2008-10-03 03:38:42 GMT)
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As far as I know, this means that the test is performed with materials, substances, allergens in there original form. (p.ex. real food, undiluted/unprocessed substances, without solvents, alcohol, ..... )
So how I understand it it should read "epicutaneous test performed with native substances".

On epicutaneous testing, high molecular weight substances like food or latex proteins will at times give positive reactions only on previously involved or possibly even inflamed skin because of better penetration. Suspected foods often give positive skin reactions only with the **native substance** since commercial extracts are often unreliable. The choice of vehicle is also important: agents suspended in alcoholic solutions or suspensions cause more rapid and fleeting reactions whereas reactions to agents in vaseline last longer. Equivocal tests results should be repeated, simulating the exposure of the patient with the suspected agent.
http://www.john-libbey-eurotext.fr/en/revues/medecine/ejd/e-...