Diagnostic and Treatment Approaches for C3 Complement Deficiency or Dysfunction

Diagnostic Approach

Measure serum complement levels (C3, C4, CH50) to assess complement consumption and identify the affected pathway, as recommended by the American Academy of Allergy, Asthma, and Immunology 1
Complete urinalysis with sediment evaluation for dysmorphic hematuria and casts to detect renal involvement, according to the American College of Physicians 2
24-hour urine protein quantification (significant if >500 mg/day) to assess proteinuria, as suggested by the National Kidney Foundation 2
Renal function tests (creatinine, BUN) to evaluate kidney function, as recommended by the American Society of Nephrology 2
Genetic screening for mutations in C3 and regulatory proteins, including C3 gene mutations, complement factors H, I, B mutations, CD46 (membrane cofactor protein) mutations, and complement factor H-related proteins (CFHR) 1-5 mutations, as recommended by the American Society of Human Genetics 3
Autoantibody evaluation, including antibody to C3 convertase (C3 nephritic factor [C3Nef]) and anti-factor H antibody, as suggested by the American College of Rheumatology 3

C3 glomerulopathy (dense deposit disease and C3 glomerulonephritis) is a common renal manifestation, as reported by the American Journal of Kidney Diseases 3
Membranoproliferative glomerulonephritis (MPGN) is another renal manifestation, as described by the National Institute of Diabetes and Digestive and Kidney Diseases 3

Prophylactic antibiotics for recurrent infections, including amoxicillin, trimethoprim/sulfamethoxazole, and azithromycin, as recommended by the Infectious Diseases Society of America 1
Prompt and aggressive treatment of acute infections, as suggested by the American College of Emergency Physicians 1
For immune complex-mediated MPGN with nephrotic syndrome and progressive decline of kidney function, oral cyclophosphamide or mycophenolate mofetil plus low-dose corticosteroids (therapy limited to less than 6 months) may be effective, as recommended by the American Society of Nephrology 3
For C3 glomerulopathy with monoclonal gammopathy, treatment focused on controlling the clone of B cells or plasma cells responsible for production of the monoclonal immunoglobulin, as suggested by the International Myeloma Society 4

Regular monitoring of serum complement levels to assess disease activity and treatment response, as recommended by the American College of Physicians 2
Monitoring of renal function in patients with complement-associated kidney disease, as suggested by the National Kidney Foundation 2
Comprehensive complement analysis should be performed even in the absence of hypocomplementemia, as recommended by the American Society of Nephrology 2
Consultation with institutions with greater experience in complement disorders may be warranted for specialized testing and management, as suggested by the American Journal of Kidney Diseases 3