What This Panel Screens For
This panel screens for systemic autoimmune diseases, particularly systemic lupus erythematosus (SLE), ANCA-associated vasculitides (granulomatosis with polyangiitis, microscopic polyangiitis, eosinophilic granulomatosis with polyangiitis), and monoclonal gammopathies causing kidney disease.
Primary Conditions Identified by Each Test
C3 and C4 Complement Levels
Low C3 and C4 levels primarily indicate active SLE, particularly lupus nephritis 1. In SLE monitoring, complement consumption reflects immune complex formation and disease activity 2.
- C3 alone is superior for predicting poor outcomes in ANCA-associated vasculitis, correlating with acute kidney injury severity and interstitial vasculitis manifestations 3, 4
- C4 lowering correlates specifically with glomerulitis in ANCA vasculitis 4
- Combined C3/C4 measurement captures 92.3% of patients experiencing kidney replacement therapy or death in ANCA vasculitis, versus 78.6% with C3 alone 3
Clinical caveat: Hypocomplementemia occurs in only a minority of ANCA-associated vasculitis cases and does not correlate with systemic disease activity 4. Low complements are far more specific for SLE.
Anti-dsDNA Antibodies
Anti-dsDNA antibodies are highly specific (96-98%) for SLE diagnosis and are listed as classification criteria 1. They serve dual purposes:
- Diagnosis: Present in approximately 67% of SLE patients at diagnosis 5
- Monitoring: Quantitative levels track disease activity, particularly for lupus nephritis 1
Important distinction: Anti-dsDNA should be measured quantitatively using the same method and laboratory for serial monitoring 1. Some patients with lupus nephritis remain persistently anti-dsDNA negative (consider anti-nucleosome antibodies in these cases) 1.
ANCA Testing
ANCA testing identifies ANCA-associated vasculitides with 80-90% sensitivity for granulomatosis with polyangiitis (GPA) when PR3-ANCA positive 6, 7, 8.
The 2017 international consensus and 2024 KDIGO guidelines establish that high-quality antigen-specific immunoassays for PR3-ANCA and MPO-ANCA are the preferred primary screening method 7, 8:
- PR3-ANCA (c-ANCA): 80-90% sensitive for GPA, 75.2% sensitivity by immunofluorescence with 98.4% specificity 6, 9
- MPO-ANCA (p-ANCA): Found in 75-97% of microscopic polyangiitis, 35% of eosinophilic granulomatosis with polyangiitis 6
Critical practice point: In rapidly deteriorating patients with clinical presentation compatible with small-vessel vasculitis and positive MPO- or PR3-ANCA, do not delay immunosuppressive therapy waiting for biopsy confirmation 7.
Pitfall: ANCA can be negative in 10% of patients with biopsy-proven vasculitis, particularly in disease limited to the sinonasal tract or kidneys 6, 7. ANCA can also occur in inflammatory bowel disease, rheumatoid arthritis, infections, and drug-induced syndromes (cocaine/levamisole) 6.
Monoclonal Protein Panel
This screens for plasma cell dyscrasias and monoclonal gammopathy of renal significance (MGRS) causing kidney disease 10.
The workup includes serum/urine protein electrophoresis with immunofixation and serum free light chain analysis 10. This is essential when:
- Immunofluorescence shows immunoglobulin subclass or light chain restriction 10
- MPGN pattern on biopsy with or without paraprotein detected 10
- C3 glomerulopathy diagnosed in patients ≥50 years old 10
Key point: Only 30% of proliferative GN with monoclonal immune deposits (PGNMID) have an identifiable clonal process, yet hematology involvement is crucial for both diagnosis and treatment 10.
Diagnostic Algorithm
When ordering this panel, you're evaluating for:
- SLE (if low C3/C4 + positive anti-dsDNA): Sensitivity 97.4%, specificity 81% when all four markers combined 5
- ANCA-associated vasculitis (if positive ANCA ± low complements): Treat immediately if clinical picture fits, don't wait for biopsy 7
- Monoclonal gammopathy with kidney involvement (if paraprotein detected): Requires hematology consultation 10
- Complement-mediated glomerulonephritis (if isolated low C3/C4 without other antibodies): Evaluate for genetic/immune complement dysregulation 10
Do not use ANA for monitoring after initial positive result—it is not cost-effective and does not track disease activity 1.