Cell-bound complement activation product (CB-CAP) profiling and scoring serve as diagnostic biomarkers for patients to determine whether a patient who has not met at least four American College of Rheumatology (or similar e.g. SLICC) criteria for a definite Lupus diagnosis should be classified as exhibiting a pre-existing condition that this document refers to as pre-Lupus. This document also describes methods for determining whether a patient who has been determined to exhibit pre-Lupus has progressed to exhibiting definite Lupus.