Complement Tests

A comprehensive evaluation of the complement system requires three types of data to offer to your patient the best chance of accurately defining the cause and consequence of complement dysregulation.

  • Complement Biomarker Profiling – Specific biomarkers provide a detailed and mechanistic understanding of the underlying complement pathology to add to disease definition. By defining a complement pathway signature, biomarkers can be useful to follow disease activity and/or severity in the clinical setting.
  • Measuring Complement Function – Measuring and following complement activity can predict disease status (active vs. inactive) and response to therapy.
  • Identifying Acquired Drivers of Disease – Identifying acquired drivers of disease such antibodies to C3 convertase, factor H and factor B provides a metric to follow a patient’s clinical course.

Antibody Tests

Nef Activity (by IFE) Indications for screening: C3 nephritic factors can be detected in approximately 80% of DDD and 65% of C3 Glomerulonephritis patients and interfere with innate mechanisms that would otherwise control C3 convertase activity. C3Nefs can also be detected in patients with partial lipodystrophy, meningococcal meningitis and post-streptococcal acute glomerulonephritis.

C3NeF (by C3CSA) Indications for screening: C3 nephritic factors can be detected in approximately 80% of DDD and 65% of C3 Glomerulonephritis patients and interfere with innate mechanisms that would otherwise control C3 convertase activity. C3Nefs can also be detected in patients with partial lipodystrophy, meningococcal meningitis and post-streptococcal acute glomerulonephritis.

C5NeF (by C3CSAP) Indications for screening: C3/C5 nephritic factors can be detected in approximately 80% of DDD and 65% of C3 Glomerulonephritis patients and interfere with innate mechanisms that would otherwise control C3 convertase activity. C3/C5Nefs can also be detected in patients with partial lipodystrophy, meningococcal meningitis and post-streptococcal acute glomerulonephritis.

C4Nef Indications for screening: C4 nephritic factors can be detected in more than 10% of patients with C3 Glomerulopathy and interfere with innate mechanisms that would otherwise control C3 convertase activity.  C4Nefs can also be detected in patients with post-infectious glomerulonephritis, systemic lupus erythematosus and meningococcal disease

Factor H Autoantibody (FHAA) Indications for screening: Factor H autoantibodies have been associated with DDD (Dragon-Durey, et al., 2005, Moore, et al 2010) and they are identified in approximately 10% of patients with aHUS. MLPA testing is indicated in those patients who have been identified to have Factor H Autoantibodies.

Factor B Autoantibody (FBAA) Indications for screening: Factor B autoantibodies have been associated with DDD (Strobel, et al. 201; Chen, et al. 2011) Although rare, FB autoantibodies should be considered in the evaluation of patients with DDD, C3GN and aHUS.


Biomarker Tests

Complement C3 Plasma Level Indications for screening: Consumption of C3 is consistent with activation of the alternative pathway of complement in patients with DDD and C3GN see Zhang et al. Defining the complement biomarker profile of C3 glomerulopathy, CJASN 2014).  C3 levels are also reduced in 30% to 50% of patients with atypical hemolytic uremic syndrome (aHUS) carrying Factor H variants, and 20% to 30% of patients carrying Factor I variants, a finding consistent with complement-dependent disease (Loirat & Frémeaux-Bacchi, 2011).   Screening is appropriate in patients with complement-mediated renal diseases.

Complement C3c Fragment Assay Indications for screening: The common pathophysiological basis of both Dense Deposit Disease (DDD) and C3 Glomerulonephritis (C3GN) is dysregulation of the AP complement cascade. Consumption of AP complement components is dependent on the degree of dysregulation of both the C3 and C5 convertases.  Plasma C3c levels are elevated in both DDD and C3GN as compared to controls (p<0.001).

Complement C4 Fragment Assay Indications for screening: Complement C4 (MW: 188 kDa), a central complement component in the classical and lectin pathways, is required to generate C4b2a, the C3 convertase of the classical pathway. C4 is cleaved to C4a (anaphylatoxin; 8 kDa) and C4b (180 kDa). C4b binds C2, and after removal of non-catalytic domain on C2, the C4b2a complex is formed. Unlike plasma C3, plasma C4 levels are typically normal in aHUS and C3G, however this test helps to rule out other complement-mediated renal diseases.  Screening is appropriate in patients with aHUS, DDD and C3GN.

Complement Factor B Level Assay Indications for screening: The common pathophysiological basis of both Dense Deposit Disease (DDD) and C3 Glomerulonephritis (C3GN) is dysregulation of the AP. Consumption of AP complement components is dependent on the degree of dysregulation of the C3 and C5 convertases. In both DDD and C3GN, patients often have lower levels of factor B as compared to controls (p<0.001) consistent with dysregulation of the C3 convertase in both diseases (see Zhang et al. Defining the complement biomarker profile of C3 glomerulopathy, CJASN 2014).  Screening is appropriate in patients with complement-mediated renal diseases.

Complement Ba Fragment Assay Indications for screening: The common pathophysiological basis of both Dense Deposit Disease (DDD) and C3 Glomerulonephritis (C3GN) is dysregulation of the AP complement cascade. Consumption of AP complement components is dependent on the degree of dysregulation of the C3 and C5 convertases. Plasma levels of Ba are elevated in both DDD and C3GN as compared to controls (p<0.001), consistent with consumption of C3 in both diseases.  Screening is appropriate in patients with DDD and C3GN.

Complement Bb Fragment Assay Indications for screening: The common pathophysiological basis of both Dense Deposit Disease (DDD) and C3 Glomerulonephritis (C3GN) is dysregulation of the AP. Consumption of AP complement components is dependent on the degree of dysregulation of the C3 and C5 convertases. Plasma levels of Bb are elevated in both DDD and C3GN as compared to controls (p<0.001) consistent with dysregulation of the C3 convertase in both diseases (see Zhang et al. Defining the complement biomarker profile of C3 glomerulopathy, CJASN 2014).  Screening is appropriate in patients with complement-mediated renal diseases.

Plasma Properdin Level Assay Indications for screening: The common pathophysiological basis of both Dense Deposit Disease (DDD) and C3 Glomerulonephritis (C3GN) is dysregulation of the AP. Consumption of AP complement components is dependent on the degree of dysregulation of the C3 and C5 convertases. While properdin plasma levels are often reduced in both DDD and C3GN, properdin levels are generally lower in C3GN as compared to DDD (p<0.01) (see Zhang et al. Defining the complement biomarker profile of C3 glomerulopathy, CJASN 2014).  Screening is appropriate in patients with complement-mediated renal diseases.

Complement C5 Level Assay Indications for screening: The common pathophysiological basis of both Dense Deposit Disease (DDD) and C3 Glomerulonephritis (C3GN) is dysregulation of the AP. Consumption of AP complement components is dependent on the degree of dysregulation of the C3 and C5 convertases. Plasma C5 levels are reduced in both DDD and C3GN as compared to controls (p<0.001 for both diseases) (see Zhang et al. Defining the complement biomarker profile of C3 glomerulopathy, CJASN 2014).  Screening is appropriate in patients with complement-mediated renal diseases.

Soluble C5b-9 (sMAC) Indications for screening: The soluble form of the membrane attack complex can be elevated in some complement-mediated renal diseases such as aHUS, C3GN and DDD. This testing may be helpful to help determine future therapies.

Complement Factor I Level Assay Indications for screening: Complement Factor I (FI; MW: 88 kDa) is an important regulator of complement activity triggered through the classical and alternative pathways. FI limits complement activation by cleaving surface-bound and fluid-phase C3b and C4b, preventing the assembly of the C3 and C5 convertases. Patients with FI variants may have reduced plasma FI levels and/or function, and are at-risk to develop atypical hemolytic uremic syndrome or C3 glomerulopathy.  Screening is appropriate in patients with aHUS.

Complement Factor H Level Assay Indications for screening: Complement Factor H (FH; MW: 155 kDa) is an important fluid-phase and cell-surface regulator of alternative pathway (AP) activity. Patients with FH variants or FH autoantibodies may have reduced plasma FH levels and/or function, and are at-risk to develop atypical hemolytic uremic syndrome or C3 glomerulopathy.   Screening is appropriate in patients with aHUS, DDD and C3GN.


Complement Pathway Functional Tests

Complement CH50 Assay (CH50eq) Indications for screening: CH50 measures total hemolytic activity of the classical and terminal pathways using sensitized sheep erythrocytes. CH50 can be low if complement components in the classical pathway (C1, C4, C2, C3) or terminal pathway (C5 through C9) are reduced or absent. Since most patients with C3G (especially DDD) have exceedingly low plasma C3 levels, their CH50s are also typically low.  Screening is appropriate for many diseases associated with complement activation.

Hemolytic Assays of Complement Activity Indications for screening: Abnormal hemolytic activity may be seen in serum from patients with aHUS if these patients carry either a genetic variant in complement or have acquired risk factors for aHUS such as Factor H autoantibodies. An abnormal hemolytic activity assay may also be seen in serum from patients with DDD if these patients carry either genetic variants or acquired factors for DDD such as C3 nephritic factors. Screening is appropriate for patients with aHUS and biopsy-proven DDD.

Alternative Pathway Functional Assay (APFA) Indications for screening: Dense deposit disease (DDD) and C3 glomerulonephritis (C3GN) are two ultra-rare renal diseases. Both diseases are characterized by fluid-phase dysregulation of the AP that often leads to partial or complete consumption of circulating complement components, including complement C3, factor B, properdin and C5 (see Zhang et al. Defining the complement biomarker profile of C3 glomerulopathy, CJASN 2014). As a consequence, APFA can be low.  Screening is appropriate for patients with dysregulated AP activity.

C3b Deposition Assay Indications for screening: Testing using the C3b Deposition Assay is appropriate for patients whith complement-mediated TMAs such as atypical hemolytic uremic syndrome (aHUS).

ADAMTS-13 Tests

ADAMTS-13 Activity Indications for screening: ADAMTS13 activity is absent in the inherited form of TTP (Upshaw-Schülman syndrome) and reduced (<10%) when a patient has an inhibitor of ADAMTS13 such as is seen in the usual/acquired TTP. Reduced ADAMTS13 Activity levels can also be seen in patients with aHUS (<60%).