Why Is A Split Urine Sample Collected For A Pre-Employment Drug Screen?

A split urine sample is collected because it is more reliable than a standard test. By splitting a sample in two, any testing mistakes can be accounted for.
How a split urine test works:

• First of all, a sample of urine is taken from the subject, just as if a non-split test was being performed.
• The sample is then split into two, and both specimens are sent to the same laboratory for testing.
• One of the two samples is drug-tested straight away and the other is left in storage.
• If the first sample tests positive for traces of illegal and abusive substances, then the subject can request that the second sample be tested.
• The laboratory will ask the subject if they are on any prescription medication, as these can sometimes cause false positive results.
• If the subject hasn't been taking any prescription medication, then they can request to have the second sample (the one in storage) tested. This sample can be tested at the same lab or a completely different one.
• If the second sample tests positive as well, then the subject fails the test. If it's negative then the test will have to be taken again.
• The advantage that a split urine test has is that it ensures that no lab errors could have contributed to the result.