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Complement test
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The complement test is a blood test. It measures the amount of a group of proteins called the complement system, or how active they are. Nine of them are the main ones.
These proteins do not act on their own: they work in a chain, and each one switches on the next. That is why a single test, the CH50, measures the activity of the whole set all at once. First you check the whole set and then the parts: if the CH50 comes back abnormal, you can measure the nine levels one at a time to see which one is failing.
Among them, C3 and C4 are the ones most often ordered separately. Levels that come back outside the normal range can point to another condition or to an autoimmune disease, one in which the body's defenses attack the body itself.
In brief
A complement test measures the amount or the activity of the complement proteins in the blood; nine of them are the main ones.
They work in sequence, each one activating the next; CH50 measures the total activity, and if it comes back abnormal, all nine can be measured separately.
First you check the whole row, then you check tile by tile.
C3 and C4 are the ones most often ordered individually; abnormal levels can point to an autoimmune disease or another condition.
Sources (1)
- MedlinePlus, U.S. National Library of MedicineComplement Blood Test, MedlinePlus Medical TestPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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