Confused about drug screen vs. drug test

hey guys. i took a drug screen today (for pre-employment) for the first time so i don't know what it's all about. but i was told that a drug screen was diferent than a drug test. i just did a urine test and i thought it wass gonna be instant results but they said they were gonna said it to a lab or something. does this mean they are gonna to be more sensitive or is it gonna be the standard 50 ng/ml cuttoff? i don't get it. or are they going to start out doing gc/ms? help guys i am worried. i smoked like 2.5 weeks ago and all but i am worried that its gonna exeed the 15 ng/ml cuttoff with gc/ms?

i looked on the website of the lab i went to and it said that for "screening" the cutoff is 50 ng, but that if tested postitive, it will be examined through gc/ms and the cutoff then would be 15 ng. i tested negative twice with the at-home test, which is supposed to be like a drug screen at labs... but since it's shipped off to a diff. lab does that mean it's most likely done through gc/ms? anyone, help????

na man those home test do not even conmpare to a lab test...... but to answer the question.......i really dont know. i havent taken a test in years

Yes a screen and test are not the same, a screen or EMIT is a immunoassay or dip test like a home test. EMIT recognizes a composite of all 31 metabolite concentrations. The psychoactive ingredient in marijuana is 11-nor-D-9-tetrahyrocanibinol (THC). This is oxidized by the body and comes out as 31 different metabolites. The most prevalent form is 11-nor-D-9-tetrahyrocanibinolic acid (THCA). Thats why it's at a higher cut-off level 50 ng/mL.
The GC/MS cutoff number is lower at 15 ng, because the machine only identifies one of the 31 metabolites, which is the 11-nor-D-9-tetrahyrocanibinolic acid, mentioned previously. To pass, that one metabolite must be below the 15 ng cutoff level.
If your positive on a screen it will be sent for a GC/MS for a conformation