Complement Factor B (Serum) – Quantitative

Why This Test Is Done

Doctors may order a complement factor B test if you have symptoms of immune system disorders, such as frequent infections, autoimmune diseases, or signs of complement system dysfunction. It can also be part of a broader evaluation for conditions like hereditary angioedema or other genetic immune deficiencies.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast for a few hours before the test if it’s part of a larger blood workup, but this is not always required. Bring any medications or supplements you’re taking to your appointment.

A healthcare provider will draw blood from a vein in your arm using a small needle. You may feel a brief pinch, but the procedure is quick and usually not painful. The blood sample will be sent to a lab for analysis.

You can return to your normal activities immediately. There may be a small bruise or slight discomfort at the injection site, but this typically fades within a day or two. If you experience excessive bleeding, swelling, or signs of infection (like increased pain or redness), contact your doctor.

Results may be compared to a reference range provided by your healthcare provider. Low levels of complement factor B can indicate immune system dysfunction, while very high levels may suggest certain inflammatory conditions or laboratory artifacts. Your doctor will interpret the results in the context of your overall health and symptoms.

Interpreting results can be complex and depends on your medical history, so always discuss findings with your healthcare provider.