Most blood and urine tests for the presence of heroin differ from alcohol test results as these measure a metabolite of heroin (morphine) which is itself active. Heroin is metabolised to 6-monoacetyl morphine and then to morphine in the blood. Alcohol produces clear dose-related impairment as measured by breath, blood or urine tests. The presence of morphine in urine merely signifies that the person had used or been exposed to opiates at some point prior to the test.