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C-Reactive Protein Complement Test and Lupus

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C-Reactive protein including C3, C4, and CH50 are heavily involved in immune system function and lupus. Testing for these proteins can even help make a definitive diagnosis.

Imagine a series of dominos, lined up in a row. Except, in this case, when the last domino falls, it kills bacteria and viruses invading the body. In this analogy, the dominos are a series of over 15 different proteins called C-reactive proteins. The chain reaction they create in the body is essential to how our bodies protect themselves from invaders.

However, in autoimmune diseases such as systemic lupus erythematosus (SLE), the dominos are turned against the body. The push that sends the dominos tumbling down are a person’s own cells. 

C-reactive proteins and lupus

For people living with lupus, there are typically issues at the C3 or C4 ‘dominos’ so these blood tests provide a proxy measure for the total inflammation levels within the body. Unfortunately, the results do not provide insight into where in the body the inflammation is occurring.

More than 75% of people with lupus have C-reactive protein deficiencies, but the exact role of complement proteins in lupus is still unclear. Researchers believe that complement proteins may be involved in how the body clears out dead or dying cells. When things go awry, they start attacking healthy cells as well.

C-reactive protein complement tests are used to:

  • help diagnose lupus
  • monitor inflammation and lupus flares
  • assess how well medications are working
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How do you test C-reactive proteins?

When blood is drawn for a C-reactive protein test, it is usually taken from a vein or a finger. No preparation, like fasting, is needed before the blood draw. The protein test is conducted using the whole blood sample (as opposed to plasma or just blood cells).

The test measures 2 things in the blood sample:

  1. The amount of the specific proteins
  2. The activity level of the proteins

The lab test then looks at how the ‘dominos’ fall and which proteins are leftover. 

Because C-reactive protein levels can vary from person to person over time, there is a range of what is considered to be normal. Different laboratories set the ‘normal’ levels for their tests differently. To get the best interpretation of your lab results, talk to your doctor when you get them.

Is it worth getting tested?

Yes, it is likely that your lupus treatment team will order C-reactive protein tests throughout your care journey. C-reactive protein complement tests can’t measure disease activity because the levels fluctuate naturally over time. However, if you have potential symptoms of lupus, you should think about taking this blood test. Alongside symptoms like the malar rash and other blood tests and biopsies, a C-reactive protein complement test can help fill in a piece of the puzzle and aid diagnosis.

Comments (11)

11 thoughts on “C-Reactive Protein Complement Test and Lupus

    1. Not true. I get my C reactive proteins and sed rate tested every 4 weeks. In fact I have never spent the night in the hospital aside from having my children. Which was long before I was diagnosed.

    2. My primary which is an internist was able to have the test ran through our lab assigned by my insurance. That was in July 2017. Just had bloodwork On the 24th too see where my levels are now!!

  1. I’ve had all these test done back in 1989 and go in every week and have it done because I stay I’ll constantly because of my lupus. They gave me 10 years to live at first diagnoses but God continues to keep me going with my diagnostic drs etc and God.

  2. My bloodwork in 09/19 showed my c reactive level at 9.5 and categorized as extremely high. Did methotrexate in 2 90 day intervals and had horrible reactions, this was 2017! Hurricane Irma hit Florida Where I live and due to stress from all of this my body swelled so bad i could barely move and my bp was through the roof. I had to be hydrated and a week of bp meds but had a reaction to that. I have a neurological disorder called RSDS/CRPS which causes many complications with stability & sensitivities along with severe spine issues, I have not been to an RA because most want you on pain meds and i don’t take any and ive lived with major pain over 20 years, I was originally told SLE but recently after having shngles i was told cutaneous lupus or medical induced, I’m confused. Any help would be appreciated,

  3. Where can one find more information on CRP levels? I have lupus and RA. I was never tested for CRP until RA was diagnosed. My CRP is all over the place, and I would like to know more. My doctor says that there is little information on it.

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