Since kidney biopsies are not repeated at every flare of lupus nephritis, a noninvasive predictor of renal pathology would be very useful in choosing therapy. A biomarker that can forecast lupus nephritis flare well before thresholds of proteinuria, renal function, and urine sediment that signal clinical flare are reached would be a valuable tool. Osteoprotegerin (OPG), a member of the tumor necrosis factor (TNF) receptor family, has been identified as a regulator of bone resorption. Increased plasma concentrations of OPG have been found in patients with diabetes mellitus and have been associated with diabetic microvascular manifestations.