A blood sample taken from a vein in your arm
C-reactive protein (CRP) is an acute phase reactant, a protein made by the liver that is released into the blood within a few hours after tissue injury, the start of an infection or other inflammation. Increased concentrations in the blood can be found after a heart attack, in sepsis, and after a surgical procedure. It is often the first evidence of inflammation or an infection in the body, with rising concentrations frequently preceding pain, fever or other clinical indicators. The concentration of CRP in the blood can jump a thousand-fold in response to inflammation and can be valuable in monitoring disease activity.
The CRP blood test is not diagnostic but it provides information to the doctor as to whether inflammation is present. This information can be used by the doctor in conjunction with other factors, such as signs and symptoms, physical examination and other tests to determine if someone has an acute inflammatory condition, or if they are experiencing a flare-up of a chronic inflammatory disease. The doctor may then follow up with further testing and treatment.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in your arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
CRP is useful in assessing patients with:
- Inflammatory bowel disease (IBD)
- Some forms of arthritis
- Autoimmune diseases
- A suspected serious bacterial infection, such as sepsis
- Pelvic inflammatory disease (PID)
- CRP is also used to monitor patients after surgery or other invasive procedures to detect the presence of an infection during the recovery period.
While measuring CRP in the blood is not specific enough to diagnose a particular disease, it does serve as a general, non-specific marker for infection and inflammation which can alert medical professionals that further testing and treatment may be necessary.
When is it requested?
Because the concentration of CRP increases in severe cases of inflammation, the test is requested when acute inflammation is a risk (such as from an infection after surgery) or suspected based on patient symptoms. It is also requested to help evaluate chronic inflammatory conditions, such as rheumatoid arthritis and lupus (SLE) and is often repeated to determine whether treatment has been effective. This is particularly useful for inflammatory conditions since CRP levels drop as inflammation subsides.
What does the test result mean?
A high or increasing amount of CRP in your blood suggests that you have an acute infection or inflammation but it does not help in identifying its location or the condition causing it. In people with chronic inflammatory conditions, high concentrations of CRP suggest a flare-up or that treatment has not been effective.
If the CRP concentration in your blood drops, it means that you are getting better and inflammation is being reduced.
When your results fall below 10 mg/L, you no longer have clinically active inflammation.
Is there anything else I should know?
CRP concentrations can be elevated in the later stages of pregnancy, with use of birth control pills or in women taking hormone replacement therapy. Higher levels of CRP have also been observed in the obese.
Another test to monitor inflammation is called the erythrocyte sedimentation rate (ESR). Both CRP and ESR are elevated in the presence of inflammation, but the concentration of CRP in the bloodstream rises and falls faster than ESR. CRP levels may therefore fall to normal if you have been treated successfully, such as for a flare-up of arthritis, but your ESR may remain abnormal for a while longer.
What are chronic inflammatory diseases?
Chronic inflammatory diseases are diseases that lead to the development of long-lasting or frequently recurring inflammation. They can be caused by a number of different pathological conditions. Examples include rheumatoid arthritis, lupus, and inflammatory bowel disease (e.g. Crohn's disease or ulcerative colitis).
What is the difference between regular CRP and hs-CRP tests?
Both tests measure the same molecule in the blood. The high sensitivity CRP (hs-CRP) test is not widely used but may be requested on seemingly healthy people to help assess their risk for heart disease. The regular CRP test is requested in patients who are at risk of bacterial or viral infections (such as after surgery) or in patients with chronic inflammatory diseases (such as rheumatoid arthritis).
On This Site
Tests: High-sensitivity C-reactive protein (hs-CRP); erythrocyte sedimentation rate (ESR)
Conditions: Arthritis, Autoimmune Disorders, Inflammatory Bowel Disease, Pelvic Inflammatory Disease, Systemic Lupus Erythematosus, Sepsis, Vasculitis, Meningitis and Encephalitis
Elsewhere On The Web
Analyte Monographs alongside the National Laboratory Medicine Catalogue (AMALC): CRP
MEDLINEplus Medical Encyclopedia: C-reactive protein
National Rheumatoid Arthritis Society