The aim of this study is to compare the predictive validity and reliability of PEth testing at detecting alcohol use in post liver transplant patients. A prospective cohort study will be used to test the primary hypothesis. Subjects enrolled in the study will be followed for 12 months with biomarker levels drawn at baseline, six and 12 months. The baseline interview will inquire about the previous 30 day alcohol and tobacco use; lifetime and 12 month Diagnostic and Statistical Manual-IV criteria for alcohol abuse and/or dependence; prior alcohol treatment; history of abstinence prior to transplant; co-morbid medical issues; and depression. The six and 12 months interview will focus on previous 30 day alcohol use. The baseline, six and 12 months interviews will be conducted face-to-face at each site. While many patients who receive a transplant do not live near the academic medical center that performed the surgery patient, they normally have a transplant clinic visit 1-2 times per year. Medical records and transplant databases will be assessed to assess the other variables of interest.

Patients who have a positive PEth will be asked to have a confirmatory test performed 10-14 days after a positive result (PEth >20ng/ml). The rationale for this procedure is to determine the test retest reliability of this marker and as well as being able to correlate levels of drinking with changes in biomarker levels over time. There is limited information on the length of time PEth levels remain elevated in transplant patients after drinking episodes.

Hypothesis H.1. PEth will have a significantly higher "area under the Receiver Operating Characteristic (ROC) curve" in a sample of post-transplant patients who report any alcohol use in the past 30 days compared to the control group.

H.2. PEth will have a significantly higher "area under the ROC curve" in a sample of post-transplant patients who report daily alcohol use of >40 grams/day (three drinks/day) in the past 30 days compared to the control group.

H.3. PEth will have a significantly higher "area under the ROC curve" in a sample of post-transplant patients who report heavy episodic drinking (>60 grams of alcohol, eight or more occasions in the past 30 days) compared to the control group.

H.4. PEth levels will be <20 ng/ml in the control sample of 50 post transplant patients who do not have a history of alcohol dependence or alcohol related liver disease.

H.5. The test-retest reliability of PEth will be >0.90.

Inclusion Criteria:

• men and women 18 years and over
• Participant must have received a liver transplant after January 1, 2003
• Participant must be six months or more post-transplant
• Mini-mental status score of greater than or equal to 20
• Participant must be well enough to participate in the research procedures over a 12 month period
• Participant must continue to be followed by the transplant center

Exclusion Criteria:

• Individuals who do not consent

Transplant center patients