An interactive session at the 69th AACC Annual Scientific Meeting & Clinical Lab Expo, The Complement System: Overview and Laboratory Testing (72412), aims to turn participants into “complement whizzes” who can go back to their labs with a fresh perspective on complement testing.

Clinical laboratory professionals have yet to embrace complement testing as an area of expertise. At the same time, clinicians have little knowledge of the challenges labs face with respect to testing. “We are here at AACC raising awareness to complement to bridge that gap,” session moderator Maria Alice Willrich, PhD, a chemist with the Mayo Clinic’s laboratory medicine and pathology departments, told CLN Stat.

This afternoon short course will take place from 12:30 p.m. to 2 p.m. on July 31 and is worth 1.5 CE credits.

Part of the innate immune system, the complement system functions “complementarily” to antibodies and phagocytic cells, removing microbes and damaged cells from circulation by tagging them, then promoting inflammation and cell lysis, Willrich said. A number of functional and inhibitory proteins circulate as inactive precursors until a “trigger” is present to activate the cascade.

Three known pathways may activate the complement system: the classical (CP), the lectin (LP), and the alternative pathways (AP). “The CP is activated by an antigen-antibody immune complex, whereas the LP is activated directly by mannose-containing bacterial surfaces. The AP is constantly active at low levels, by spontaneous hydrolysis of C3 in the presence of properdin, and has a surveillance role,” said Willrich. “The recognition molecules which trigger activation of each pathway differ; however, all pathways converge to a C3-mediated amplification loop and end with the terminal pathway.”

Willrich’s presentation will include an overview of complement testing and interpretation for clinical laboratorians. Co-presenter Ashley Frazer-Abel, PhD, assistant professor of research at the University of Colorado School of Medicine, will follow up with a talk on understanding the complement in clinical laboratories.

The speakers plan to review the main lab tests used to characterize complement dysfunction, which usually involve serum or plasma. Tests such as traditional hemolytic assays and others measure complement function or activity, complement components concentration, activation products or autoantibodies.

Other topics of discussion include some of the genetic variants responsible for complement dysregulation and limitations associated with the methodologies and testing. “We also have a few cases that will help the audience put the new knowledge into perspective,” Willrich added.

A number of factors are driving utilization of complement system testing right now. Historically, people thought of complement deficiencies in relation to immunodeficiencies, manifesting with severe or frequent infections, Willrich said.

Recently, however, “complement has been recognized for its role in inflammatory states, autoimmune disorders, and even in vision loss.  This requires new considerations for complement testing. Ten years ago, there was not much recognition of the complement system involvement in these conditions and also nothing you could do to control it,” she explained.

Use of monoclonal antibody eculizumab, a drug with an annual cost exceeding $500,000, and other complement inhibitors to treat complement-related disorders have driven the need for proper complement testing for diagnosis and monitoring the impact of therapy.

To cover such a large expense, health insurance companies often need proof that patients’ disease is complement-mediated and that the drug will provide therapeutic benefits, Willrich said. This has given labs a new role: to aid clinicians in making these diagnoses and show evidence of complement dysregulation through testing. “Different institutions have developed different serological panels to detect complement dysregulation,” she said.

Frazer-Abel recalls when she first started researching complement and gave lectures on hereditary angioedema (HAE), a disorder marked by spontaneous swelling of the hands, face, and gut that can prove fatal if it strikes the upper airways.

“Physicians would tell me that they would never bother to order a complement test to diagnosis the disease as it could not change their treatment,” she told CLN Stat.

Once a complement-specific drug targeting HAE hit the U.S. market, Frazer-Abel began getting calls about which complement test to use and what to do when available tests weren’t sufficient. “Now, with the success of eculizumab, we are getting calls from nephrologists and other areas of medicine if they find they have to remember that seemingly arcane complement cascade,” Frazer-Abel said.

As these drugs become more widespread, tests once suited for complement deficiencies aren’t as effective in testing for complement function nuances or in informing clinicians about the effectiveness of therapy, Frazer-Abel said. “This in turn calls on laboratorians to be ready to diagnose, follow treatment, and be able to bring on complement assays to meet developing needs,” she noted.

As the heat-labile fraction of the immune system, Willrich said instability and heat sensitivity are the main challenges associated with testing the complement system.

“Samples cannot be exposed to room temperature, and preanalytical diligent care is a must for good results. Also, some complement pathways are always active at low levels, so you may have complement activation occurring in vitro after the blood is drawn, which can also affect test results, depending on what you are measuring,” Willrich explained. “Since the complement system is a cascade of proteins, one needs multiple tests for a comprehensive overview of complement function.”

Isolating a complement disorder usually requires a panel approach. The assays also aren’t standardized or harmonized. “The reference intervals and performance between methods is often not interchangeable across laboratories,” she added.

Internationally, an official committee of the International Complement Society has been working to improve the harmonization and quality of complement assays, according to Frazer-Abel. So far, this effort has resulted in seven rounds of external quality assessment.

In the United States, a small group of labs have been active in complement. At least in Willrich’s practice, method comparisons and academic collaborations have resulted in process improvements. “I think if laboratories understand the importance of the preanalytical stringent sample collection requirements and have a better understanding of the complement cascade to make informed interpretations in the post-analytical step, this is a win,” she said.

To get all of the details on complement testing, register today for the for the 69th AACC Annual Scientific Meeting & Clinical Lab Expo in San Diego, July 30–Aug. 3.