A good way to differentiate between the two is; speedy screen and testing takes time; a screen is cheap and fast (speedy screen), a test is slow and expensive (testing takes time). A drug screen is just that a "Screen". Drug screening is a cost-effective method to quickly review all samples. Drug screens are highly reactive, but not highly selective. This can result in false positives for substances like ibuprofen, poppy seeds, and over the counter sinus medications. The screen cannot tell the difference between ibuprofen and the drug metabolite. For example, over 60% of screens that test positive for amphetamines later prove to be negative on a drug test. This means 6 out of 10 people screening positive for amphetamines are truly negative.
With statistics this bad, why do labs even use drug screens? The answer is simple: Money! It would be way too expensive for labs to run a drug test on each sample. This cost would then be passed onto the customer who would then decide drug testing is too expensive and drop the program.
To further complicate things there are several types of screens. The first is the on-site screen, which is manually performed. These are popular with parole departments and pre-employment situations for lower paying hourly jobs. This occurs because the company or agency simply wants to save time and money and does not really care about results. The screen is given and if the person passes every thing is okay. If the person fails, it is no job, fired, or back to jail. Not a very fair system considering if they tested positive for amphetamines, there is a 60% chance the sample would test negative on a drug test.
The second type of screen is used in conjunction with a drug test. This is the method used by most major corporations. If the sample passes the screen, the testing process is done and the individual is given a passing status. If the sample fails the screen, it moves on to the drug test or confirmation test. For a test to be labeled "Drug Test" a gas chromatography/mass spectroscopy (GC/MS) has to be performed on all positive screens. GC/MS is an extremely precise piece of equipment, which measures the molecular size, charge, and weight of the atoms in the drug metabolites. Due to the precision of the machine it can tell the difference between poppy seeds and opiates, ibuprofen and THC metabolites, nasal sprays and amphetamines.