Osteopontin (OPN) is a protein present in the bone and other tissues. Elevated levels of OPN have been observed in several autoimmune diseases including lupus. Investigators from a group called Systemic Lupus International Collaborating Clinics (SLICC) examined data from 344 people with lupus over the course of five years to determine whether raised OPN is a reliable biomarker for lupus. Specifically, they wanted to know if increased levels of OPN could predict damage; reflect current disease activity; or if increased OPN levels are associated with certain disease phenotypes (characteristics).