C4A and systemic lupus erythematosus: When comparing FLC concentrations of SLE patients with low levels (n = 23, and n = 30, respectively) and SLE patients with normal levels (n = 22, and n = 15, respectively) of the complement factors C3 and C4, respectively, an association was demonstrated between C4 complement consumption and elevated concentrations of serum FLCs (Fig 7) (p = 0.073 and p = 0.030 regarding C3 and C4 concentrations, respectively).