The presence of codeine can be the result of either heroin or codeine use
. The presence of morphine can be the result of the use
of heroin, codeine, or morphine. Relative levels of codeine and morphine can help determine their origin.
With the new higher cutoff levels (2,000 ng/ml), Heroin use will generally only produce a positive test result for a day after single use (somewhat longer with chronic use).
I hope this helps, if you have any more questions please feel free to ask.