C5 Complement, Functional
Label Mnemonic: C5FX
Epic Lab Code: LAB7398
Downtime Form: A-1a Miscellaneous Request
Commercial Mail-out Laboratory
5231 RCP
Specimen Instructions:
Specimen is suggested to be drawn from a fasting patient.
Collection Medium:
Red top tube 5 mL (Clot Activator)
Preferred Minimum: 1.0 mL Serum
Absolute Minimum: 0.5 mL Serum
Delivery Instructions:
Mix well and place on wet ice. Keep on ice and deliver to laboratory immediately.
Turn Around Time:
3 working days upon receipt at reference laboratory
Reference Range:
29-53 unit/mL
Interpretive Data:
Low levels of complement may be due to inherited deficiencies, acquired deficiencies, or due to complement consumption (e.g., as a consequence of infectious or autoimmune processes).

Absent C5 levels in the presence of normal C3 and C4 values are consistent with a C5 deficiency. Absent C5 levels in the presence of low C3 and C4 values suggest complement consumption.

Normal results indicate both normal C5 protein levels and normal functional activity.
Useful For:
Diagnosis of C5 deficiency

Investigation of a patient with an undetectable total complement (CH50) level.

The total complement assay (COM Complement, Total, Serum) should be used as a screen for suspected complement deficiencies before ordering individual complement component assays. A deficiency of an individual component of the complement cascade will result in an undetectable total complement level.

Absent (or low) C5 functional levels in the presence of normal C5 antigen levels should be replicated with a new serum specimen to confirm that C5 inactivation did not occur during shipping.
Automated Liposome Lysis Assay
CPT Code:
See Additional Information:
Fasting Specimen Requirements