C7 Complement, Functional, Serum
Use
This test is useful for diagnosing C7 deficiency and investigating a patient with an undetectable total complement level. Patients with deficiencies in the late complement proteins, such as C5, C6, C7, C8, and C9, are unable to form the membrane attack complex (MAC) and are more susceptible to neisserial infections. C7 deficiency, though relatively rare, is primarily associated with neisserial infections but is also seen in conditions such as systemic lupus erythematosus, rheumatoid arthritis, scleroderma, and pyoderma gangrenosum.
Special Instructions
Fasting for 12 hours is preferred but not required. The total complement assay should be used as a screen for suspected complement deficiencies before ordering individual component assays. Proper specimen handling to ensure the complement system is not activated before testing is crucial. If low C7 functional levels are noted with normal antigen levels, repeat testing with a new serum specimen is advised.
Limitations
Complement levels can be nonfunctional despite being present. It is essential to detect C7 deficiency with a functional assay. Complement consumption due to infections or autoimmune processes can also lower complement levels. Absent C7 levels in the presence of normal C3 and C4 are consistent with C7 deficiency, while low C7 with low C3 and C4 suggests complement consumption. Inappropriate test selection and improper specimen collection can lead to diagnostic confusion.
New York Approved
Methodology
Automated Analyzer (Clinical Chemistry)
Biomarkers
LOINC Codes
- 87724-1
- 87724-1
Result Turnaround Time
1-3 days
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
1 mL
Minimum Volume
0.5 mL
Container
Serum gel or red top tube; transfer to plastic vial
Collection Instructions
After collection on wet ice, allow specimen to clot. Centrifuge at 4°C, aliquot serum into a plastic vial and freeze within 30 minutes. If not frozen immediately, place on dry ice.
Patient Preparation
Fasting for 12 hours is preferred but not required.
Causes for Rejection
Gross hemolysis and gross lipemia are causes for rejection.
Stability Requirements
| Temperature | Period |
|---|---|
| Frozen | 14 days |