Using clinical and laboratory data from our prospective cohort of patients with SLE, we investigated the association of serum TNC levels with Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2 K) scores and conventional laboratory markers of disease activity, such as anti–double-stranded DNA antibodies (anti-dsDNA), C3, C4 and anti-nucleosome antibodies. The gene discussed is C4A; the disease is systemic lupus erythematosus.