1. Presented by Alisha Ware, MD and reviewed by William Clarke, PhD

An adult patient with a history of alcoholic cirrhosis status post liver transplant presented with symptoms of chronic transplant rejection and progressive weakness. On presentation, the patient had elevated liver enzymes (ALT 99 U/L, AST 138 U/L), total bilirubin (15 mg/dL), and creatinine (2.1 mg/dL, baseline 1.5-1.8 mg/dL). The patient also had hyponatremia (Na 134 mmol/L) and hyperkalemia (K 5.3 mmol/L). In addition to concerns for chronic rejection, the clinical team was concerned that the patient's worsening liver function was due to possible alcohol abuse.

Question:
What laboratory test is specific for long-term alcohol abuse?