Expert: Dr Alan Galbraith - 10/16/2009

Question
Dear Dr Galbraith,

I recently contacted Dr Ravindra Ghooi who provided some valuable advice.  My husband recently failed a Urine Drug Test for Cannabis, yet he has not smoked any.  He has exposed himself to some due to his sister being a user.

Are you able to provide any advice on the following -

My husbands results came back as >85 ng/ml and then 75 ng/ml, is it fair to say that passive inhalation is NOT a valid explanation for failing such a test.  I either believe my husband has suffered due to passive inhalation or he's possibly eaten a little bit.  It has been stated that the amount found he 'has taken' cannabis and that the level of THC can not be attributed to passive inhalation of cannabis smoke, and finally no other substance would give a positive result for THC.

Please help.....

Answer
Dear Lauren

I am surprised you are from the UK as all questions referring to abnormal drug tests seem to emanate from the US where many laboratories are sub-standard and frequently report false positives. However, in your case, considering there are two quantitative tests giving similar results they should be correct considering the sensitivity of modern analytical tests.

I tend to agree that passive inhalation should not give such such high results as the cut off rate for passive smoking has been given as 65 ng/mL. Your husband's figures are not much higher than this and it could still be passive smoking and perhaps ingestion of THC from other sources. See http://www.idmu.co.uk/pdfs/drugtest.pdf Also, does his sister bake with cannabis, a not to uncommon scenario with user.

Hope this is of some help. The website is a bit technical in places but I am sure that some of what you want to know can be found there.

Regards

Alan Galbraith