C-reactive protein

A C-reactive protein (CRP) test is used to detect inflammation. It measures levels of CRP, a protein that is released into the blood in response to inflammation. Levels of CRP start to rise soon after the start of inflammation or an infection. Normally, you have low levels of CRP in your blood. A CRP test may be ordered if your doctor suspects you have an infection, is checking for an infection after surgery, thinks that you may have an autoimmune disorder such as rheumatoid arthritis or lupus, or is monitoring your treatment of an inflammatory disease to see if it is working.

Why get tested?

CRP is made in the liver and sent out into the bloodstream in response to inflammation. It plays an important role in the immune process which is your body's way of protecting your tissues if you have an infection or have been injured. Inflammation causes redness and swelling in the affected area, but it is essential to the healing process. Some autoimmune disorders and chronic diseases also cause inflammation.

Levels start to rise soon after the start of inflammation or an infection.  Levels can rise very steeply and then drop relatively quickly as soon as the inflammation passes. This makes measuring CRP blood levels a useful way of checking for inflammation and monitoring the effectiveness of any treatment you need to have.

Normally, you have low levels of CRP in your blood.  A CRP test might be ordered if your doctor:

• suspects you have an infection
• is checking for infection after surgery
• thinks that you may have an autoimmune disorder such as rheumatoid arthritis or lupus 
• or is monitoring treatment of an inflammatory disease to see if it is working.

The CRP test cannot show where inflammation is located and it cannot diagnose a particular disease. The test is usually ordered along with other tests.

Having the test

Sample

Any preparation?
None

Your results

Your results will be presented along with those of your other tests on the same form.  You will see separate columns or lines for each of these tests.  

Although a high CRP result is not specific for a particular condition it is a sensitive marker of inflammation and so is a useful test in many situations. There is often no clear connection between the level of CRP and the severity of the inflammation.

• A high or increasing amount of CRP in your blood suggests that you have an acute infection or inflammation - most infections and inflammations result in CRP levels above 10 mg/L.
• If the CRP level in your blood drops it means that you are getting better and inflammation is reducing.
• A CRP test can be useful in differentiating between bacterial and viral infections. A very high CRP level is more likely to occur in a bacterial rather than a viral infection. A normal CRP level is unlikely if there is a bacterial infection.

Reference intervals

• Reference intervals are the range of results expected in healthy people. 
• When compared against them your results may be flagged high or low if they sit outside this range.
• Many reference intervals vary between labs so only those that are standardised or harmonised across most laboratories are given on this website.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation. Your results need to be interpreted by your doctor.

CRP test results can vary between laboratories, so it is a good idea that repeat tests are carried out by the same laboratory to avoid confusion. 

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms.   It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

Any more to know?

Another test to monitor inflammation is the erythrocyte sedimentation rate (ESR). Both CRP and ESR give similar information. However, CRP appears and then disappears sooner than changes in the ESR. Thus, your CRP level may fall to normal if you have been treated successfully, such as for a flare-up of arthritis, but your ESR might still be abnormal for a while longer.

CRP is not affected by as many things as is ESR, which can be affected by periods and pregnancy as well as some medications. This makes CRP a better test for some types of inflammation. Because ESR is an easily performed test and requires only relatively simple equipment, many doctors still use it as an initial test when they think a patient may have inflammation.

More information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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