This article was last reviewed on
This article waslast modified on 5 November 2020.
At a Glance
Why Get Tested?

To identify the presence of inflammation, to determine its severity, and to monitor response to treatment. 

When To Get Tested?

When your doctor suspects that you might be suffering from an inflammatory disorder (as with certain types of arthritis and autoimmune disorders or inflammatory bowel disease) or to check for the possibility of infection (especially after surgery)

Sample Required?

A blood sample taken from a vein in your arm

Test Preparation Needed?


On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

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.

Accordion Title
Common Questions
  • How is it used?

    CRP is useful in assessing patients with:

    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).