A 55-year-old man is evaluated in follow-up after a recent routine screening for antibody to hepatitis C virus (HCV) was positive. His medical history is unremarkable; he has not used illicit drugs or had any history of blood transfusions. He currently feels well and takes no medications.

Vital signs and physical examination are normal.

Laboratory studies reveal a positive HCV antibody test, but HCV RNA testing is negative. The serum alanine aminotransferase level is normal.

Which of the following is the most appropriate diagnostic test to perform next?