Provided herein are methods for treating a patient having NASH who has been determined to have a particular threshold level of serum Pro-C3 (e.g., greater than 10 ng/ML) by administering to the patient a modified Fibroblast growth factor 21 (FGF-21) in an amount and with a frequency sufficient to treat NASH. Also provided are methods for monitoring responsiveness of a patient having NASH to treatment with a modified FGF-21, the method comprising: determining the serum Pro-C3 level in a blood sample from the patient obtained during or after treatment, wherein: a decreased serum Pro-C3 level in the blood sample from the patient obtained during or after treatment, as compared to the serum Pro-C3 level in a blood sample from the patient obtained prior to treatment with the modified FGF-21, indicates that the patient is responsive to treatment with the modified FGF-21.