This algorithm is intended for use with additional UpToDate content on low C1q.
C1q: complement component 1q; HUVS: hypocomplementemic urticarial vasculitis syndrome; AAE-C1-INH: acquired angioedema due to deficiency of C1 esterase inhibitor; GI: gastrointestinal; CBC: complete blood count; BUN: blood urea nitrogen; UA: urinalysis; UPCR: urine protein/creatinine ratio; ANA: antinuclear antibody; C4: complement component 4; C3: complement component 3; LCV: leukocytoclastic vasculitis; SPEP: serum protein electrophoresis; UPEP: urine protein electrophoresis; SLE: systemic lupus erythematosus; C1-INH: C1 inhibitor. * Interpretation of an abnormal result should be based on the reference range reported with that result. ¶ HUVS is an autoimmune disorder that may occur as a primary syndrome or as a clinical feature that is part of another diagnosis, such as SLE. Δ AAE-C1-INH is a rare disorder. It often occurs in association with monoclonal gammopathy, low-grade lymphoma, or SLE. ◊ C1-INH should be discontinued for at least 1 week before obtaining diagnostic complement studies in patients receiving C1-INH concentrate.
