Complement Component C3, C4, CH50

This panel may be useful in evaluating patients with clinical suspicion of systemic lupus erythematosus (SLE). This panel includes measurements of complement component 3 (C3), complement component 4 (C4), and total hemolytic complement (CH50).

Low levels of C3 and/or C4 are included in the 2019 SLE classification criteria from EULAR (European League Against Rheumatism/American College of Rheumatology) [1], whereas the 2012 Systemic Lupus International Collaborating Clinics classification criteria for SLE include low levels of C3, C4, or CH50 [2]. Without SLE diagnostic criteria in place, SLE classification criteria are often used by clinicians to guide diagnosis. However, the current classification criteria have not been tested for diagnostic purposes and should not be used alone to exclude the diagnosis of SLE [1,2].

Other immunologic biomarkers that may aid in the diagnosis of SLE include antinuclear antibodies and specific antibodies to double-stranded DNA and Smith [3]. Measurement of C3 and C4 may also help monitor activity and remission of SLE [4].

The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

References
1. Aringer M, et al. Arthritis Rheumatol. 2019;71(9):1400-1412.
2. Petri M, et al. Arthritis Rheum. 2012;64(8):2677-2686.
3. Kavanaugh A, et al. Arch Pathol Lab Med. 2000;124(1):71-81.
4. Mosca M, et al. Ann Rheum Dis. 2010;69(7):1269-1274.