A C-reactive protein (CRP) blood test is used to identify inflammation or infection in the body.
C-reactive protein is released into the blood by the liver shortly after the start of an infection or inflammation. CRP is an early indicator of these problems because its levels usually start to rise in the blood before symptoms, such as fever and pain, appear.
Why It's Done
Doctors may order the C-reactive protein test if symptoms suggest any kind of inflammation, particularly related to inflammatory bowel disease (IBD), arthritis flare-ups, or an autoimmune disorder such as rheumatoid arthritis or lupus.
It may also be used to detect infections in vulnerable patients, such as those who've just had surgery. The CRP test also may help determine whether treatment for any of these conditions is working, because CRP levels drop quickly as inflammation subsides.
No special preparations are needed for this test. Make sure to tell your doctor about any medications your child is taking because certain drugs might alter the test results.
On the day of the test, having your child wear a short-sleeve shirt can make things easier for your child and the technician who will be drawing the blood.
A health professional will usually draw the blood from a vein. For an infant, the blood may be obtained by puncturing the heel with a small needle (lancet). If the blood is being drawn from a vein, the skin surface is cleaned with antiseptic, and an elastic band (tourniquet) is placed around the upper arm to apply pressure and cause the veins to swell with blood. A needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe.
After the procedure, the elastic band is removed. Once the blood has been collected, the needle is removed and the area is covered with cotton or a bandage to stop the bleeding. Collecting blood for this test will only take a few minutes.
Either method (heel or vein withdrawal) of collecting a sample of blood is only temporarily uncomfortable and can feel like a quick pinprick. Afterward, there may be some mild bruising, which should go away in a few days.
Getting the Results
The blood sample will be processed by a machine. The results are commonly available after a few hours or the next day.
Generally, an elevated CRP level indicates an infection or inflammation somewhere in the body. But the CRP alone can't tell doctors where the problem is or what's causing it, so further testing may be necessary.
The C-reactive protein test is considered a safe procedure. However, as with many medical tests, some problems can occur with having blood drawn, such as:
fainting or feeling lightheaded
hematoma (blood accumulating under the skin causing a lump or bruise)
pain associated with multiple punctures to locate a vein
Helping Your Child
Having a blood test is relatively painless. Still, many kids are afraid of needles. Explaining the test in terms your child can understand might help ease some of the fear.
Allow your child to ask the technician any questions he or she might have. Tell your child to try to relax and stay still during the procedure, as tensing muscles and moving can make it harder and more painful to draw blood. It also may help if your child looks away when the needle is being inserted into the skin.
If You Have Questions
If you have questions about the C-reactive protein test, speak with your doctor.