Advanced Diagnostic Laboratories

Factor I Level

Test Code

FIL

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. Complement activation is controlled by multiple proteins at various steps in each pathway to prevent injury to autologous tissues. Factor I is the key regulator of the complement pathways due to its ability to degrade activated complement proteins C3b and C4b in the presence of cofactors such as factor H, C4b-binding protein, complement receptor 1 or CD46.

The factor I RID assay is a method for quantitation of the complement regulatory factor I protein. Complete deficiency of factor I can lead to complement consumption resulting in severe recurrent infections, glomerulonephritis or autoimmune disease. Low or absent factor I levels can be associated with low C3 levels

Collect

Plasma from a lavender top (K2- EDTA) tube is the only acceptable sample type. The EDTA collection tube must be completely filled with blood to ensure the correct blood to anticoagulant ratio. Invert tube several times for thorough mixing of blood anticoagulants. Keep the EDTA tube filled with blood on ICE until centrifugation.

Patient Prep

Within 30 (±5) minutes of venipuncture, centrifuge the collection tube at 1600 (± 200) x g (rcf) at 4°C (± 2°C) for 15 (±1) minutes. Transfer the cell-free plasma to a clean cryogenic storage tube and immediately store samples at -20°C, or freeze at -60°C or below in an ultra-low freezer.

Preferred volume: 1.0 mL plasma

Minimum volume: 0.25 mL plasma

Pediatric Collection

Minimum volume: 0.25 mL plasma

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 – greater than 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

Radial Immunodiffusion (RID)

Turnaround Time

Up to 4 weeks

Department

Complement Lab

Synonyms

RIA (Factor I Level);C3b-INA (Factor I Level);Complement (Factor I Level);KAF (Factor I Level);Radial Immuno Assay (Factor I Level)

Study Offerings

CAP/CLIA

Reference Interval

Human Male: 29 - 59 mcg/mL
Human Female: 29 - 59 mcg/mL

Interpretation

Positive results should be interpreted with other complement tests including the Factor H Function (FHF), Factor H Level (FHL), Classical Complement Pathway Activity (CM50), Alternative Complement Pathway Activity (AM50), and Complement C3 level (C3).