Are there instances when you recommend performing a kidney biopsy in patients with presumed acute interstitial nephritis who are already on steroids and have improving renal function?

The decision to perform renal biopsy in a patient with presumed allergic interstitial nephritis on steroids, who is demonstrating improvement depends on the magnitude and rate of improvement. In a patient whose magnitude and rate of improvement, I suggest that the prior acute kidney injury baseline serum creatinine will be achieved over a 7 to 14-day period while on steroids, I would not perform a renal biopsy. On the other hand, if the magnitude of improvement is minimal, despite 7 to 10 days of steroids, and the diagnosis of interstitial nephritis is uncertain, under these circumstances, I would consider performing a renal biopsy,

To expand just a bit on Dr. @Dr. First Last's comments, for me kidney biopsy should be entertained if there is question about the diagnosis or if there is consideration to change therapy that is not working. If you are certain of the underlying etiology and stopped the offending agent and steroids are improving the course then I do not see the potential benefit of a kidney biopsy since I would not change treatment. However, close follow up is still merited and if there is any question about the course, then biopsy may be reconsidered.