C-Reactive Protein (CRP)

The CRP (C-Reactive Protein) is a simple blood test that estimates the level of inflammation in the body. The C-Reactive protein is an actual protein made by the liver in response to inflammation.

The CRP is a very common test used in rheumatology. It is often used as a screening test that gives a picture of a person’s overall level of inflammation.

The CRP can be used as a first step to screen for a wide range of inflammatory diseases. An CRP is usually ordered when a person has signs and symptoms of any of the following rheumatologic diseases:

  • Rheumatoid Arthritis
  • Ankylosing Spondylitis
  • Polymyalgia Rheumatica
  • Psoriatic Arthritis
  • Systemic Sclerosis
  • Giant Cell Arteritis
  • Granulomatosis with Polyangiitis
  • Microscopic Polyangiitis
  • Eosinophilic Granulomatosis with Polyangiitis
  • Behçet’s Disease
  • Takayasu Arteritis
  • Reactive Arthritis
  • Enteropathic Arthritis
  • Raynaud’s Phenomenon

A CRP test is ordered when inflammation in the body is suspected. An elevated CRP points to increased inflammation in the body, but it doesn’t say anything about what is causing the inflammation. The CRP test can be elevated in many conditions, not just rheumatologic diseases.

Science Behind This Test

Inflammation

The word inflammation comes from the Latin word inflammare which means to set on fire. Inflamed tissues can be swollen, warm, painful, and red.

Many medical conditions or diseases can cause inflammation. A few examples include:

  • Infections
  • Uric acid crystals in gout
  • Autoimmune diseases such as Rheumatoid Arthritis can cause inflammation in the joints

Why the CRP is done

When there is inflammation in the body, evidence of this inflammation can be seen in the blood. The CRP is one type of test that can be used to estimate the level of inflammation in the body. It does not indicate why inflammation is present in the body.

CRP results

The CRP results are important to consider because:

  • It can be used to screen for a wide range of inflammatory conditions including rheumatologic diseases
  • It can be used to monitor a person’s condition after a diagnosis is made, e.g. during a flare
  • It can be used to monitor a person’s response to treatment

The best use of the CRP is to follow inflammation over time. CRP levels can go up and down for many reasons. Because of this, it is important to make sure the CRP test results “match up” with a person’s symptoms. For example, a person with Polymyalgia Rheumatica (PMR) might have an elevated CRP at diagnosis. After treatment is started, the CRP may fall. If the CRP increases again, it might be due to a flare of PMR or it might be due to an infection in the body, such as a urinary tract infection. So when CRP levels change, it is important to look at the person’s overall health status so that the right treatment decisions can be made.