C1 Esterase Inhibitor, Functional

For Specimen Integrity during Extreme Weather see the “Lockbox Usage in Extreme Weather” document at the top of this page.

Test Code

CPT Codes

Preferred Specimen
1 mL serum collected in a red-top tube (no gel)

Minimum Volume
0.2 mL

Freeze serum within one hour of time drawn.
Do not submit the sample in a glass tube. Do not thaw.

Transport Temperature

Specimen Stability
Room temperature: Unacceptable
Refrigerated: Unacceptable
Frozen: 30 days

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Grossly lipemic • Serum separator tube • Received thawed

Enzyme Immunoassay (EIA)

Setup Schedule
Monday-Saturday Afternoon Report available: Next Day

Reference Range
≥68 % Normal
41-67 % Equivocal
≤40 % Abnormal

Less than 40% of the reference functional activity indicates a likely diagnosis of hereditary angioedema or acquired C1 Inhibitor deficiency.

Clinical Significance
C1 esterase is decreased in angioedema. The inherited form is usually diagnosed in the first two decades of life. The acquired form affects primarily adults with autoimmune or lymphoproliferative disorders. Approximately 15% of patients with hereditary angioedema have a normal concentration of the protein but it is dysfunctional.

Performing Laboratory
Quest Diagnostics Nichols Institute
14225 Newbrook Drive
Chantilly, VA 20153

Last Updated: November 24, 2021

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.