In simplest terms, ANA-negative lupus is a condition in which a persons ANA - or antinuclear anitbody - test comes back negative, but the person exhibits traits consistent with someone diagnosed with lupus. The ANA test is used to screen for systemic lupus erythematosus(SLE or lupus), not diagnose it. ANA-negative lupus is believed to be less common now that the ANA test has improved senstitivity and precision.
Typically, if a person tests positive for the antinuclear antibody, it means only that the person could have lupus. Further evaluation is needed to determine if a person actually has lupus.
