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HelpTest Code C341Q Complement C3 and C4 with Anti-C1q Antibodies, Serum
Specimen Required
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 1.5 mL
Collection Instructions: Centrifuge and aliquot serum into a plastic vial
Useful For
Evaluating patients with suspected anti-C1q vasculitis
Predicting renal involvement in patients with systemic lupus erythematosus
Profile Information
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| C3 | Complement C3, S | Yes | Yes |
| C4 | Complement C4, S | Yes | Yes |
| AC1Q | Anti-C1q Antibodies, IgG, S | Yes | Yes |
Method Name
AC1Q: Enzyme-Linked Immunosorbent Assay (ELISA)
C3, C4: Nephelometry
Reporting Name
C3 and C4 with Anti-C1q, IgG, SSpecimen Type
SerumSpecimen Minimum Volume
0.9 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 7 days | |
| Frozen | 21 days |
Reference Values
C3:
75-175 mg/dL
C4:
14-40 mg/dL
AC1Q:
<20 U/mL (Negative)
20-39 U/mL (Weak Positive)
40-80 U/mL (Moderate Positive)
>80 U/mL (Strong Positive)
Interpretation
A positive result for anti-C1q antibodies may support a diagnosis of anti-C1q vasculitis or renal involvement in patients with systemic lupus erythematosus in the appropriate clinical context.
A negative result indicates no detectable IgG antibodies to C1q and does not rule out a diagnosis.
A decrease in C3 levels to the abnormal range is consistent with disease activation in systemic lupus erythematosus.
Clinical Reference
1. Dragon-Durey MA, Blanc C, Marinozzi MC, van Schaarenburg RA, Trouw LA. Autoantibodies against complement components and functional consequences. Mol Immunol. 2013;56(3):213-221
2. Defendi F, Thielens NM, Clavarino G, Cesbron JY, Dumestre-Perard C. The immunopathology of complement proteins and innate immunity in autoimmune disease. Clin Rev Allergy Immunol. 2020;58(2):229-251
3. Marzano AV, Maronese CA, Genovese G, et al. Urticarial vasculitis: Clinical and laboratory findings with a particular emphasis on differential diagnosis. J Allergy Clin Immunol. 2022;149(4):1137-1149
4. Hristova MH, Stoyanova VS. Autoantibodies against complement components in systemic lupus erythematosus - role in the pathogenesis and clinical manifestations. Lupus. 2017;26(14):1550-1555
5. Jachiet M, Flageul B, Deroux A, et al. The clinical spectrum and therapeutic management of hypocomplementemic urticarial vasculitis: data from a French nationwide study of fifty-seven patients. Arthritis Rheumatol. 2015;67(2):527-534
6. Jennette JC, Falk RJ, Bacon PA, et al. 2012 revised International Chapel Hill Consensus Conference Nomenclature of Vasculitides. Arthritis Rheum. 2013;65(1):1-11
7. Mehregan DR, Hall MJ, Gibson LE. Urticarial vasculitis: a histopathologic and clinical review of 72 cases. J Am Acad Dermatol. 1992;26(3 Pt 2):441-448
8. Damman J, Mooyaart AL, Seelen MAJ, van Doorn MBA. Dermal C4d deposition and neutrophil alignment along the dermal-epidermal junction as a diagnostic adjunct for hypocomplementemic urticarial vasculitis (anti-C1q vasculitis) and underlying systemic disease. Am J Dermatopathol. 2020;42(6):399-406
9. Marto N, Bertolaccini ML, Calabuig E, Hughes GR, Khamashta MA. Anti-C1q antibodies in nephritis: correlation between titres and renal disease activity and positive predictive value in systemic lupus erythematosus. Ann Rheum Dis. 2005;64(3):444-448
10. Fava A, Wagner CA, Guthridge CJ, et al. Association of autoantibody concentrations and trajectories with lupus nephritis histological features and treatment response. Arthritis Rheumatol. Published online July 4, 2024. doi:10.1002/art.42941
Day(s) Performed
C3, C4: Monday through Friday
AC1Q: Wednesday
Report Available
2 to 8 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
86160 x2
83520
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| C341Q | C3 and C4 with Anti-C1q, IgG, S | In Process |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| C3 | Complement C3, S | 4485-9 |
| C4 | Complement C4, S | 4498-2 |
| AC1Q | Anti-C1q Antibodies, IgG, S | 44702-9 |