Advanced Diagnostic Laboratories

Classical Complement Pathway Activity (CH50)

Test Code

CM50

Description

The complement system is part of our innate immune response. It is vital to our defense against invasive microorganisms. Complement activation can occur through the classical, lectin and alternative pathway, which then converge to a common terminal pathway. Activation of the complement pathway(s) results in the generation of biologically active peptides, also known as complement split products, and referred to as anaphylatoxins (C4a, C3a, C5a) which protect us from invasive microorganisms by enhancing inflammation, facilitating the clearance of immune complexes and apoptotic cells, enhancing cellular, and antibody immune responses, and altering vascular permeability, as well as smooth muscle contractility.

Complement deficiency can lead to life-threatening infections well as long-term autoimmune conditions such as systemic lupus erythematosus (SLE) and hereditary angioedema (HAE). The CH50 hemolytic assay is a sensitive method for detection of total classical complement activity or lack thereof. Severe or recurrent infections that produce strong activation of the classical complement pathway may lower CH50 levels below normal. Genetic or acquired complement deficiency involving the classical complement pathway components (C1q, C1r, C1s, C2, C4, and C3) as well as terminal complement components (C5, C6, C7, C8, and C9) may also lower CH50 levels. The CH50 assay can also be utilized to monitor response to anti-complement therapies.

Collect

Serum from a Red top tube is the only acceptable sample type. Draw blood into a serum collection tube. The collection tube should be completely filled with blood. Invert tube several times to initiate the clotting process. Keep the collection tube filled with blood at room temperature for 30-60 minutes to allow the blood to clot.

Patient Prep

Centrifuge the collection tube at 1600 (± 200) x g (rcf) at 4°C (± 2°C) for 15 (±1) minutes. Affix tube label to a polypropylene cryogenic storage tube. Immediately transfer the cell-free serum to the cryogenic tube on ice and immediately store the cryogenic tube at -60°C or below in an ultra-low freezer.

Preferred volume: 1.0 mL serum

Minimum volume: 0.25 mL

Pediatric Collection

Minimum volume: 0.25 mL serum

Unacceptable Conditions

Thawed samples or samples stored at room temperature prior to shipment

Storage Transport Temp

Ship samples overnight in a well-insulated container on dry ice. We receive samples Monday - Friday. Avoid sending samples on the weekend and holidays to ensure that samples arrive frozen.

Stability

-60°C or below in an ultra-low freezer - up to 2 years

Notes

Additional tests may be needed for confirmatory testing or reflex testing.

To prevent unnecessary delays in testing, please send one aliquot per test request.

Performed

Monday - Friday

Methodology

Hemolytic Assay

Turnaround Time

Up to 4 weeks

Department

Complement Lab

Synonyms

Hemolytic Assay (Classical Complement Pathway Activity), Classical Complement Pathway Activity, Complement (Classical Complement Pathway Activity), CM50

Study Offerings

CAP/CLIA

Reference Interval

176-382 Units/mL

Interpretation

Low CH50 level is indicative of a reduction, absence, and/or inactivity of any components of the classical complement pathway and/or terminal complement pathway. Anti-complement therapy with C5 inhibitors including Eculizumab or Ravulizumab is associated with complete loss or reduced CH50 level.