Complement Component C4a, Plasma Test
This test measures C4a, in its stable form called C4a-des-arg, in a plasma sample. Quest describes C4a as released when the complement protein C4 is cleaved during activation of the classical or lectin complement pathways.
About this test
The test uses an ELISA method to measure C4a-des-arg in plasma collected in an EDTA tube and submitted in a protease inhibitor transport tube. Quest describes elevated C4a-des-arg levels as an indicator of recent complement system activation.
Quest notes that the liver can increase production of C3 and C4 during acute inflammation, which means total C3 and C4 levels can appear normal even when complement activation has occurred. An elevated C4a-des-arg level can still reflect that activation even when those other complement measures look unremarkable.
Test details
| Collection | Quest patient service center |
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Quest resources
Additional details
What this test looks at
The test reports a single value: the level of Complement Component C4a in a 2 mL frozen plasma sample, measured by Enzyme Linked Immunosorbent Assay (ELISA).
This test isn't part of the Celio Health store at the moment, so it can't be ordered or requested here. The test menu lists everything that can.
Laboratory results should always be interpreted by a licensed clinician who knows your health history. This page is information about a test, not medical advice.
Frequently asked questions
What does this test measure?
It measures C4a, in its stable form C4a-des-arg, in a plasma sample, using an ELISA method. C4a is released when complement protein C4 is cleaved during activation of the classical or lectin pathways.
How is the sample collected?
The test uses a 2 mL frozen plasma sample, collected in an EDTA tube and submitted in a protease inhibitor transport tube.
Do I need to prepare for this test?
No preparation instructions are listed for this test, though people follow any instructions their ordering clinician provides.
Why measure C4a instead of just total C3 and C4?
Quest notes that the liver can raise C3 and C4 production during acute inflammation, so those totals can look normal even when complement activation has occurred. An elevated C4a-des-arg level can still reflect that activation.