C1q Antibody, IgG

  • Assess risk for lupus nephritis development in individuals with SLE
  • Assess global SLE disease activity

See Related Tests for other tests for SLE or connective tissue disease

Systemic lupus erythematosus (SLE) is an autoimmune disease with multiorgan involvement. Approximately 37-45% of patients with SLE will develop lupus nephritis, which negatively impacts patient survival.  Testing for C1q antibodies assists in evaluating the risk of lupus nephritis development. 

Disease Overview

Physiology

C1q antibodies are associated with active glomerulonephritis in patients with SLE.  The presence of antibodies in patients with SLE indicates a higher risk for developing severe clinical manifestations of the disease. Specifically, the presence of C1q antibodies correlates with renal activity and flares, and the absence of antibodies indicates a low probability of lupus nephritis. 

Test Interpretation

Sensitivity/Specificity

  • Clinical sensitivity and specificity vary based on disease population and disease state
  • Analytical sensitivity and specificity vary based on disease population and disease state as well as testing platform

Results

  • Negative: 0-19 units
  • Equivocal: 20-39 units
  • Positive: ≥40 units

Limitations

  • Not all patients with lupus nephritis will be positive for C1q antibodies
  • The presence of C1q antibodies is not specific for SLE
    References