The rule of thumb with ADV testing is that if there is cause to doubt a result or if there is a positive result then have a different type of test by a different place done. Don't panic, don't go to any form of extreme, and don't readily accept a result when there is room for doubt. That's it in a nutshell. There is a lot of info about why this approach makes sense, who does testing, why tests aren't 100% accurate, etc. in the Archives of BOTH the FML http://listserv.cuny.edu/archives/ferret-search.html and the FHL http://fhl.sonic-weasel.org and in ADV websites http://www.ferretcongress.org for links to those and a lot more useful stuff in the critical reference section. When ADV testing is under discussion it best to recall that absolutes fit for almost nothing except the statements that testing makes sense and that ADV when it takes it off is a real horror. [Posted in FML issue 4215]