A clinician calls and says the laboratory made an error on the opiate screen he had ordered for one of his patients to detect methadone, which was being prescribed for this patient. The clinician states that the patient always takes his/her methadone at the correct time each day, yet the urine opiate screen is negative. The clinician also wonders why the urine creatinine is flagging abnormal (it is 15 mg/dL).
Why is the opiate screen negative if the patient is taking methadone regularly as prescribed?
What does the abnormal creatinine result probably indicate?