Low levels of complement may be due to inherited deficiencies, acquired deficiencies, or due to complement consumption (eg, as a consequence of infectious or autoimmune processes).
Absent (or low) C2 levels in the presence of normal C3 and C4 values are consistent with a C2 deficiency.
Low C2 levels in the presence of low C3 and C4 values are consistent with a complement-consumptive process.
Low C2 and C4 values, in the presence of normal values for C3 is suggestive of C1 esterase inhibitor deficiency.
As with all complement assays, proper sample handling is of utmost importance to ensure that the complement system is not activated before clinical testing.