THC Testing.

[GrndIIlusion]

No I'm not asking how to pass one.

 

I'm asking how they work. Recently my brother had to undergoe a urinalysis at his job and i've been wondering how they work.

 

So, THC is fat soluble. So when you're getting rid of it wouldn't be coming out the other end? What does a drug test actually test for?

[insane_alien]

there are a number of ways to test for THC. but they all look for the compound and its daughter products. THC will remain in your system for a couple of weeks depending on how heavy the usage is. this will come out in your urine for a while after the person took the drug. IIRC the most common method used for urinalysis is high performance liquid chromatography. i assume that they'll have some sortof indicator for the presence of THC as well.

 

basically, if the test develops a certain coloured strip at a certain position it has detected THC

[Dak]

iirc, thin-layer chromatography with an indicator is usually used first, 'cos it's cheaper and faster, with HPLC used to confirm (tho, i think theres a new cheaper/faster confirmation test used now, elisa maybe?).

[CharonY]

Pure ELISAs are possible, though often not that fast (due to washing steps and so on).

Mostly hybrids (immunochromatograhphic) assay are used, as in pregnancy tests. They take roughly 5 minutes and are the fastest I am aware of.

Essentially you put urine in a device which essentially contains a vial and a strip. The urine m(mobile phase) igrates along the strip (as normal thin-film chromatography). On the strip you have got immobilised drug conjugates as well as a THC directed antibody-dye conjugate.

If you don't have drugs, the antibody-dye conjugate binds to the drug-conjugate and this will result in a colouring, due to the dye. On the other hand, if drugs are present in the urine, they saturate the antibody-dye-conjugates and thus do not bind to the immobilized drug conjugates. This will result in absence of colour.