Why look at rheumatoid arthritis CRP levels?
C-reactive protein, commonly called CRP, is a protein that can be produced by the liver in response to other immune activity, especially the increase of IL-6. CRP can rise quickly in response to many inflammatory conditions such as infections or injury, helping clear out dying cells or bacteria.
Blood tests for CRP measure the amount of this protein in the blood. An increased CRP level is an indication of inflammation somewhere in the body. (However, the converse has not been proven, that low CRP proves no inflammation or disease activity exists.) Also, remember that disease activity such as damage or pain is not necessarily linked to inflammation markers (CRP). (See numbers 9 and 12 in the list of Reasons that remaining pain theories are wrong.)
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The meaning of rheumatoid arthritis CRP levels
Many doctors use CRP levels to help diagnose rheumatoid arthritis or detect unseen disease activity. A normal CRP should not rule out rheumatoid disease activity, but confusion over this causes problems for many people living with rheumatoid disease (PRD). A poster at the recent meeting of the American College of Rheumatology (ACR) defined three considerations for interpretation of rheumatoid arthritis CRP levels: The Relationship Between Elevations in CRP With Physical Function and Radiographic Progression Over the Long-term in Patients With Rheumatoid Arthritis. Let’s take a look at how rheumatoid arthritis CRP levels relate to physical function and radiographic progression (bone erosion).
3 Conclusions from an ACR poster shed light on rheumatoid arthritis CRP levels
- “CRP is an important marker of inflammation that can be used to identify patients at risk of radiographic progression, and this relationship appears more dependent on disease duration, as there were differences observed in the early vs. established patients populations.”
TAKE AWAY: Higher CRP could indicate greater risk for bone erosion, but longer disease duration increases this risk.
- “However, since radiographic progression was also observed in up to 60-75% of patients who did not have CRP elevations, regular structural evaluation remains critical until more precise markers are identified.”
TAKE AWAY: A majority of PRD with normal CRP still suffered bone erosion, so physically examining joints is more important until better blood markers are found.
- “A relationship between CRP elevations and HAQ was observed but weak, indicating that functionality may be driven by factors beyond CRP.”
TAKE AWAY: CRP is only weakly related to disability.
Rheumatoid arthritis CRP levels are imperfect indicators
Many practitioners rely on blood tests such as CRP instead of more labor-intensive physical joint examinations and health assessment questionnaires (HAQs). They may tell PRD they are doing well or have low disease activity, based on CRP levels. Investigations like this one expose the flaws in over-reliance on CRP.
An indicator should not be confused with the actual thing it is meant to measure. CRP is like a smoke alarm. If a smoke alarm goes off, then people should search for a cause, possibly a fire. However, it remains possible to have a fire without an alarm.
WHAT IMPORTANCE DO DOCTORS PLACE ON CRP?
DO BLOOD TESTS DETERMINE SO-CALLED REMISSION?
HOW MANY PEOPLE HAVE DISABILITY & DAMAGE WITH NORMAL CRP?
- Blood Tests for Rheumatoid Arthritis: What Is Their Role?
- All I Want for Christmas Is My CRP
- Textbook Rheumatoid Arthritis: Patient Input Will Replace It
- Blood Tests for Rheumatoid Arthritis, part 2
Kavanaugh A, Haraoui B, Sunkureddi P, Wolfe B, Wang L, Suboticki JL, Keystone E. The relationship between elevations in CRP with physical function and radiographic progression over the long-term in patients with rheumatoid arthritis. American College of Rheumatology Annual Meeting November 11-16, 2016. Available from: http://acrabstracts.org/abstract/the-relationship-between-elevations-in-crp-with-physical-function-and-radiographic-progression-over-the-long-term-in-patients-with-rheumatoid-arthritis/