Letter to the Editor.

The Authors Reply:

We thank Plüß and colleagues for their letter supporting our finding that aggressive histological forms of lupus nephritis may be present in patients with very little proteinuria. Although we did not find serology helpful in discriminating these patients from among all patients with low-grade proteinuria, Plüß et al. reported that higher titers of anti–double-stranded DNA antibodies and lower levels of C3 and C4 were associated with proliferative lupus nephritis. Their findings support the premise that the decision to perform a kidney biopsy in patients with systemic lupus erythematosus should not be solely based on the level of proteinuria. In the future, the pre-test probability of finding significant pathology on biopsy may be increased by applying noninvasive biomarkers of histologic activity to patients with lupus. As an example, we suggest that urine CD163, a biomarker of histologic activity in lupus nephritis and other glomerular diseases, could be used to screen these patients. Ultimately, identifying patients with lupus nephritis early is important, as many already have evidence of chronic damage by the time they manifest the standard clinical criteria for biopsy.