C-reactive protein (CRP)
The liver produces a type of acute phase protein known as C-reactive protein (CRP) and the level of C-reactive protein increases in the blood when there is inflammation in the body. When there is tissue damage the concentration of CRP in the blood can double every six hours.
Doctors can perform a C-reactive protein (CRP) test to determine if a person has a problem linked to acute infection or inflammation but not what or where the problem is. However, increased levels of CRP may prompt the doctor to perform other tests. They can also use the test to monitor how the body is responding to treatment for an infection or a long-term illness that causes inflammation.
Why is a C-reactive protein test taken?
There are several reasons why a doctor may want to have a C-reactive protein (CPR) test performed, including:
- To determine if there is infection after surgery: CRP levels normally increase within two to six hours following surgery but then return to normal by the third day; if CRP levels are elevated three days after surgery it means there is an infection.
- To keep track of an infection or disease that can cause inflammation: Inflammatory bowel disease (IBD), lymphoma ( cancer of the lymph nodes), immune system diseases such as lupus (SLE), rheumatoid arthritis ( swelling of the tissues that line the joints) and osteomyelitis (infection of the bone) are some conditions in which inflammation can be monitored with a CRP test.
- To monitor treatment of a disease such as cancer or infection: Not only do CRP levels go up quickly if you have an infection but they also return to normal quickly if you are responding to the treatment.
How is a C-reactive protein test taken?
A nurse or other healthcare professional will take a sample of blood in the same way as for any other blood test. The site for the needle may be cleaned with alcohol before inserting the needle into a vein in your arm. You may feel a quick sting as the needle is inserted, and there may be a small bruise at the site afterwards, but there are normally no other problems. However if you have a bleeding or clotting problem discuss it with your doctor.
What can a doctor determine from the test results?
If there is a high or increasing level of C-reactive protein in your blood it suggests that you have an acute infection or inflammation. If you are being tested for inflammation linked to a chronic disorder it can tell the doctor that you are having a flare-up or that treatment is not successful and the doctor may change your treatment. If the level of C-reactive protein in your blood drops it means you're getting better, and if the number falls to below 10 mg/L, you no longer have active inflammation.
Can the test be affected by other health issues?
The results of the test may not be accurate if:
- You have just exercised
- You are using an intrauterine device (IUD) or are on the contraceptive pill
- You are in the later stages of pregnancy
- You are very overweight.