Complement Total CH50 (Total Complement Activity) Biomarker Testing
It measures overall complement immune activity to help evaluate recurrent infections or autoimmune disease, with easy ordering and Quest draw access via Vitals Vault.
With Vitals Vault, you have access to a comprehensive range of biomarker tests.
Complement Total CH50 is a blood test that checks how well a major part of your immune system—called the complement system—can do its job. Instead of measuring one single complement protein, CH50 looks at the overall “team performance” of the classic complement pathway.
This test is most useful when you and your clinician are trying to make sense of patterns like recurrent serious infections, certain autoimmune conditions, or unexplained inflammation. It can also help guide which more specific complement tests to order next.
Because CH50 is a functional screening test, it is best interpreted alongside your symptoms, exam, and related labs. A single result rarely gives a complete diagnosis on its own.
Do I need a Complement Total CH50 test?
You may want a Complement Total CH50 test if you have a history of unusual or recurrent infections, especially severe bacterial infections, infections with Neisseria species, or infections that seem out of proportion to typical exposures. CH50 can be a helpful first step when your clinician is considering a complement deficiency as part of the explanation.
This test is also commonly used when autoimmune disease is on the table. In conditions like systemic lupus erythematosus (SLE), complement can be “used up” during immune complex activity, and CH50 may drop when disease is active. If you already carry an autoimmune diagnosis, CH50 can sometimes be used as one piece of monitoring—usually together with C3, C4, symptoms, and other markers.
You might also consider CH50 if prior labs show low C3 and/or low C4, or if you have findings that suggest immune-complex–driven inflammation (for example, certain kidney or skin findings) and your clinician wants a broader complement picture.
Testing supports clinician-directed care and follow-up planning, but it is not a stand-alone way to diagnose an immune disorder. If your result is abnormal, the next step is usually targeted testing (such as AH50, C3, C4, or individual complement component levels) rather than guessing based on CH50 alone.
CH50 is a CLIA-performed laboratory assay that measures functional complement activity; results should be interpreted in clinical context and are not diagnostic by themselves.
Lab testing
Order Complement Total CH50 through Vitals Vault and complete your draw at Quest.
Schedule online, results typically within about a week
Clear reporting and optional clinician context
HSA/FSA eligible where applicable
Get this test with Vitals Vault
If you are trying to understand a CH50 result—or you want to order the test to support a clinician conversation—Vitals Vault makes it straightforward to get labs without unnecessary friction. You can order Complement Total CH50 and complete your blood draw through the Quest network.
After your results post, PocketMD can help you translate the number into plain language: what “low” can mean, which companion tests often clarify the pattern, and what retest timing is reasonable based on why you tested.
If your CH50 is abnormal, you can use Vitals Vault to build a more complete follow-up plan with related labs (for example, C3/C4 or other immune markers) so you and your clinician are not making decisions from a single data point.
- Order online and draw at a Quest location
- Clear next-step guidance with PocketMD
- Easy re-testing to confirm trends over time
Key benefits of Complement Total CH50 testing
- Screens overall classic complement pathway function in one result.
- Helps investigate recurrent or unusually severe bacterial infections.
- Adds context when autoimmune disease activity (such as lupus) is being evaluated.
- Clarifies whether low C3/C4 might reflect consumption versus another issue.
- Guides which follow-up tests to order next (AH50, C3, C4, or specific components).
- Supports monitoring over time when used alongside symptoms and companion labs.
- Makes it easier to act on results with PocketMD interpretation and convenient re-ordering.
What is Complement Total CH50?
Complement is a group of proteins in your blood that work together to help your immune system clear microbes and immune complexes. When complement is activated, it triggers a cascade that can tag germs for destruction, recruit inflammation, and form a “membrane attack complex” that can puncture certain bacteria.
Complement Total CH50 (often shortened to CH50) is a functional test of the classic complement pathway. In practical terms, it asks: does your serum have enough working complement components (C1 through C9) to carry out the full classic-pathway cascade?
Because it measures function, CH50 can be low if one or more complement components are missing (inherited deficiency) or if complement proteins are being consumed faster than they are replaced (for example, during active immune-complex disease). CH50 can also be affected by sample handling because complement proteins are sensitive to heat and time.
Classic pathway vs. alternative pathway
The classic pathway is often triggered by antibodies bound to targets, while the alternative pathway can activate more directly on microbial surfaces. CH50 primarily reflects the classic pathway. If CH50 is low and your clinician suspects an alternative pathway issue, an AH50 test may be added to compare patterns.
Why a “total activity” test can be useful
Measuring individual proteins like C3 and C4 tells you how much of those proteins are present, but not necessarily whether the whole system is functioning. CH50 is a broad screen that can point you toward more specific testing when something looks off.
What do my Complement Total CH50 results mean?
Low Complement Total CH50
A low CH50 means your classic complement pathway activity is reduced. This can happen if you have an inherited deficiency of one complement component (often associated with recurrent infections, including certain meningococcal infections), or if complement is being consumed during active immune-complex inflammation. In autoimmune conditions such as lupus, a low CH50 can align with higher disease activity, especially when C3 and C4 are also low. Because pre-analytic issues can falsely lower CH50, your clinician may repeat the test or confirm with C3, C4, and/or individual complement component testing.
In-range (expected) Complement Total CH50
An in-range CH50 suggests your classic complement pathway is functioning at an expected level at the time of testing. This makes a major classic-pathway complement deficiency less likely, although it does not rule out all immune problems. If you still have symptoms such as frequent infections or autoimmune features, your clinician may look at other immune markers, antibody levels, or pathway-specific tests. Trend matters too—one normal result does not always explain intermittent symptoms.
High Complement Total CH50
A high CH50 is usually interpreted as increased complement activity, which can be seen in inflammatory states because complement proteins can behave like “acute-phase” reactants. It is less commonly used as a stand-alone flag for a specific diagnosis, and many clinicians focus more on low values. If your CH50 is high, the next step is typically to interpret it alongside other inflammation markers and your clinical picture rather than treating the number itself. Your clinician may consider whether infection, chronic inflammation, or recovery from a recent illness could be contributing.
Factors that influence Complement Total CH50
Recent infections, autoimmune flares, and other inflammatory conditions can shift complement activity. Medications and therapies that affect the immune system can also change results, so it helps to share your current medication list with your clinician. Sample handling matters: complement proteins can degrade if the specimen is not processed and stored correctly, which can make CH50 appear lower than it truly is. Finally, CH50 is a broad screen; pairing it with C3, C4, and sometimes AH50 often provides a clearer pattern than CH50 alone.
What’s included
- Creatinine, Random Urine
- Manganese, Creatinine Ratio
- Manganese, Random Urine
Frequently Asked Questions
What does a CH50 test measure?
CH50 measures the overall functional activity of the classic complement pathway. It reflects whether the complement system can complete the cascade needed to lyse target cells, which depends on multiple complement components working together.
Do I need to fast for a Complement Total CH50 blood test?
Fasting is not usually required for CH50. If you are ordering CH50 alongside other tests that do require fasting (such as lipids or glucose/insulin), follow the fasting instructions for the full set of labs.
What does a low CH50 mean in lupus?
In lupus, a low CH50 can suggest complement consumption during active immune-complex disease, especially when C3 and C4 are also low and symptoms are flaring. Your clinician typically interprets it with your clinical status and other monitoring labs rather than using CH50 alone.
What is the difference between CH50 and C3/C4?
C3 and C4 measure the amount (concentration) of individual complement proteins. CH50 measures function of the classic pathway as a whole, so it can be low even if one specific component is missing or not working properly.
What is AH50 and when is it ordered with CH50?
AH50 is a functional test of the alternative complement pathway. If CH50 is low or if your clinician suspects a pathway-specific issue, ordering AH50 alongside CH50 can help narrow down where the complement problem might be.
How often should CH50 be repeated?
Retest timing depends on why you tested. For autoimmune monitoring, clinicians may repeat it during symptom changes or at intervals aligned with other disease activity labs; for suspected deficiency or a surprising result, repeating to confirm and adding targeted complement tests is common.
Can a CH50 result be wrong because of sample handling?
Yes. Complement proteins are sensitive, and delays in processing or improper storage can reduce measured activity and make CH50 look falsely low. If the result does not fit your clinical picture, your clinician may repeat the test.