SPP1 and inflammation: Moreover, when we measured renal damage markers in the urine of patients with LN to assess whether urine OPN N-half could be a marker that can identify the site of nephron damage, we observed urine OPN N-half was correlated with urine IL-18 (Table 2, S2 Fig), suggesting that urine OPN N-half was correlated with overall renal inflammation, and not with damage to a specific nephron section, and so probably reflected the activity of LN.