A pregnant woman presents at 35 weeks reporting dark, amber-…

A pregnant woman presents at 35 weeks reporting dark, amber-colored urine and intense itching for the past 5-6 days. She states the itching is all-over her body but worse on her hands and feet, especially at night. She states that it is so bad that she cannot function at work or home. Exam reveals no rash. Which laboratory test is of most importance based on this data: