Does Low Urine Creatinine Level Indicate the Presence of Urine Alcohol in Methadone Maintenance Treatment Patients?

OBJECTIVE: We sought to test the assumption that a low urine creatinine level is indicative of the presence of alcohol in the urine of patients prescribed methadone. METHODS: This is a medical record review of 261,055 urine samples from approximately 6,000 patients prescribed methadone during a one-year period and for whom both urine creatinine and ethanol levels were simultaneously measured. We defined a creatinine level of less than 2.26 mmol/L as 'low' used a urine ethanol level of greater than 2.0 mmol/L as the reference standard for alcohol consumption. RESULTS: The sensitivity and specificity of low urine creatinine as a marker for the detection of urine ethanol are 11.9% (95% CI: 11.3, 12.5%) and 96.7% (95% CI: 96.7, 96.7%), respectively. In this patient population with a low (3.6%) prevalence of alcohol in the urine, the results correspond to a positive predictive value of 11.9% (95% CI: 11.3, 12.6%) and a negative predictive value of 96.7% (95% CI: 96.7, 96.7%), respectively. CONCLUSIONS: Low urine creatinine is a poor screening test for detecting alcohol consumption among patients on methadone. However, a normal creatinine level has a 96.7% probability of no alcohol urine present in the urine.