Is per-protocol kidney biopsy required in lupus nephritis?

Baseline kidney biopsy is recommended in lupus nephritis (LN). Biopsy allows to classify different forms of LN and differentiate other forms of renal involvement, such as tubulo-interstitial nephritis or thrombotic microangiopathy. The indications for repeat biopsy are more controversial. Some authors feel that good clinical monitoring is sufficient to assess prognosis and make therapeutic decisions. Based on the recently demonstrated discordance between clinical and histological response, some physicians recommend per-protocol biopsies either at 6 months in stable patients to verify the response to induction therapy, or after one-to-two years to assess treatment efficacy and tune the duration of maintenance therapy. Others recommend repeating kidney biopsy in case of incomplete response or to discriminate between active and chronic lesions. By definition, a per-protocol kidney biopsy differs from a repeat biopsy in that the former is foreseen at fixed timepoints, regardless of the clinical response. Although any decision should always consider the patient's overall clinical condition, there are no doubts that repeat kidney biopsy represents a useful tool in difficult cases to evaluate treatment response, modulate treatment intensity, and predict long-term renal outcome both in quiescent lupus and during flares. How to harmonize per-protocol biopsies in the LN course remains challenging.