How long would you wait before performing a kidney biopsy in a patient with possible AIN whose creatinine has plateaued, but not improved, after discontinuing the suspected offending agent?  

If the kidney function has not resolved one week after withdrawal of the suspected offending agent, I would request a biopsy.

Steroids, when initiated early with AIN, can improve long-term outcome (reduce fibrosis), and biopsy confirms your diagnosis.

It is difficult to say, because the question is somewhat abstract compared to the realities of having taken care of someone with AKI for days or weeks on end, usually in a team setting with multiple factors at play. It is easier to order a biopsy on an online platform than with a person in front of ...