Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (829 page)

Decreased in acquired conditions (see Complement Components in Plasma and Their Deficiencies table)
. Decreases in complement in acquired conditions are usually only partial and affect several components of the system. They are most commonly due to complement consumption.

Associated with arthritis

   Active systemic lupus erythematosus (SLE), especially if associated with renal disease. About 50% of patients with SLE have reductions in C3 and C4. Low complement levels correlate with more severe disease, especially with renal involvement. Normalization reflects good therapeutic results.

   Hepatitis B or C

   Essential mixed cryoglobulinemia

   Serum sickness

Associated with vasculitis

   Rheumatoid vasculitis

   Essential mixed cryoglobulinemia

   Sjögren syndrome

   Hypocomplementemic vasculitis

Associated with nephritis

   Acute poststreptococcal GN (transient decline in C3)

   IgA nephropathy

   Membranous nephropathy

   Types I and II membranoproliferative glomerulonephritis

   SLE nephritis;