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 ...

To expand just a bit on Dr. @Rudnick'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 impr...