Urine is the specimen almost all workplace drug testing uses, and it is the only one authorised for most federally regulated testing. It is cheap, the science behind the cutoff levels is settled, and the procedures for collecting it defensibly are written down in detail. This page covers the detection window, what happens when a specimen comes back dilute, and where urine testing does not answer the question you are asking.
Why it is the default
Testing conducted under Department of Transportation authority follows 49 CFR Part 40, which specifies urine as the standard specimen with oral fluid authorised in defined circumstances. That regulatory anchor pulled the entire commercial market along with it: laboratories, collection networks, cutoff levels and Medical Review Officer practice are all built around urine first. For an employer the practical consequence is that a urine programme is the cheapest to run, the easiest to staff and the best supported if a result is ever challenged.
What the detection window actually tells you
A urine test detects metabolites, which are what the body produces after processing a substance, so it reports past use rather than present impairment. Detection periods vary by substance, by dose and by the individual: a few days for most substances, longer for regular cannabis use. That distinction matters more than employers usually allow for. A positive urine result is evidence somebody used something within a window, not evidence they were impaired at work, and a policy written as though it proves impairment is a policy that will not survive being tested.
Dilute, adulterated and substituted specimens
A dilute specimen is one where the creatinine and specific gravity readings indicate excess fluid intake, which can be deliberate or entirely innocent. The standard response is a recollection rather than a finding against the donor. An adulterated specimen contains something that should not be there, and a substituted one is outside the physiological range for human urine altogether. Under the federal procedure those last two are handled as refusals to test rather than as negatives, which is why they matter far more than a dilute result and why written policies should address all three separately.
The 5 panel and its variants
The federal five are amphetamines, cocaine metabolites, opiates, phencyclidine and cannabinoids, tested at federally specified cutoff levels for regulated employees. A private employer buying a urine 5 panel is usually buying the same analyte list without the federal procedural framework around it. Everything above the five is a commercial choice, and every analyte that reaches prescription medication needs a Medical Review Officer behind it, because a lawful prescription is the most common explanation for a non-negative result on those groups.
Questions people ask about urine drug test
How long does a urine drug test detect drug use?
It varies by substance, dose and individual. A few days is typical for most substances, with regular cannabis use detectable for considerably longer. It reports past use within a window, not impairment on the day.
What happens if a specimen comes back dilute?
Usually a recollection. A dilute result means the creatinine and specific gravity readings indicate excess fluid intake, which can be deliberate or innocent, so it is not treated as a positive.
Is a urine test valid for DOT purposes?
Yes. Urine is the standard specimen under 49 CFR Part 40, with oral fluid authorised in defined circumstances. Hair is not an authorised specimen for regulated testing.
What is the difference between adulterated and dilute?
Dilute means excess fluid. Adulterated means something is in the specimen that should not be, and substituted means it is outside the human physiological range. Under the federal procedure the latter two are treated as refusals to test.