Heroin tests positive for morphine. This is because heroin is metabolized first from diacetyl morphine, then to 6-monoacetyl morphine (known as 6-MAM) and then into morphine. Codeine is often seen in low levels in the urine drug screens of heroin users.
Heroin is morphine, except with two methyl groups attached. The two acetyl groups were put onto morphine to make it cross the blood-brain barrier more easily. Unlike the rest of the body, the space between capillaries in the brain is much tighter, preventing harmful material from leaking into the fluid that bathes the fragile brain. There’s also a basement membrane at the blood-brain junction, thicker than in other areas of the body. This blood- brain barrier keeps bacteria and large molecules of many drugs from getting access to the brain.
Acetyl groups apparently make it easier for morphine to cross, or be transported, through the blood-brain barrier. With morphine, even if it’s injected, only five to ten percent of the drug crosses the blood brain barrier to reach the pleasure center, to produce the desired euphoria. However, with the addition of two methyl groups, creating heroin, around eighty to ninety percent of the drug gets across the blood- brain barrier. Thus with heroin, more drug gets to the pleasure centers of the brain. This is what makes most intravenous opioid addicts prefer heroin to injectable morphine, though personal preferences do vary.
On drug screens, we sometimes see 6-monoacetyl morphine (often called 6-MAM) as a metabolic product of heroin, and only of heroin. If this substance is seen in the urine, the person is using heroin, not morphine or other prescription opioids. This molecule is difficult to detect, since it’s in the urine briefly, from thirty minutes to twelve hours after use.
Yes, poppy seeds can cause a low-level positive for opiates, because they contain tiny amounts of morphine. But unless you eat a mountain of poppy seed muffins, the cut-off for a morphine screening test is usually set high enough to prevent positives opiate tests from poppies. But if you were to decrease the lower limit of detection of morphine, positive tests could be seen in poppy seed eaters.
With heroin, the ratio of morphine to codeine found in the urine is much higher than 2 to 1, but with prescription morphine, this ratio is less than 2:1. Thus the ratio can give an idea whether the person taking a drug test has used prescription opioid medication or heroin.
Urine drug testing for benzodiazepines can also be confusing. On most EIA tests, the antibody in the test is targeted for diazepam (Valium). However, diazepam is metabolized into several compounds, including nordiazepam, temazepam (Restoril), and oxazepam (Serax). Patients who take only Valium as prescribed can be falsely accused of taking Restoril or Serax unless the person interpreting the test results knows this
Many EIA screens don’t test positive for clonazepam, so usually a special test must be added to detect this medication.
Other tidbits: the Z medications don’t cause benzodiazepine positive results on urine drug screen EIAs. False positives for buprenorphine can be seen in patients using codeine, naltrexone, or hydrocodone.
All of these finer points of drug testing illustrate the possible hazards of drug test interpretation. Companies doing drug tests on their employees shouldn’t try to interpret the tests by themselves. They should hire doctors specially trained to interpret these tests. This type of doctor is called an MRO, for Medical Review Officer. To be an MRO, the doctor must take an initial three-day course with about 22 hours of material, and then pass a two-hour written exam to become certified. The course and test must be repeated every five years to remain certified, since the science of drug screening can advance rapidly.
Companies usually contract with MROs to look at all positive tests, and to watch for problems that could affect the integrity of the test process. If a test is positive, the MRO contacts the urine donor, and asks questions about drug use and prescriptions in an effort to decide if there was unauthorized use of a medication or drug. Otherwise, many mistakes can be made and people can lose their jobs over an error in interpretation of the drug test. If the test is positive for a prescribed medication, the only report the employer should get is that the test didn’t show any illicit drugs. In this way, the MRO also acts as a buffer between employee and employer, safeguarding the health information of the employee.
Drug addiction treatment centers usually don’t need MROs, since they are not doing screening tests, but rather tests on patients know to have issues with addiction. At most addiction treatment facilities, the medical directors interpret drug testing results. Counselors shouldn’t be expected to interpret test results on their own, and should always be able to discuss unexpected results with the program physician.