C-Reactive Protein (CPR) Test: What Is It & High Levels

C-reactive protein, also known as CRP, is a protein produced by the liver that is produced in higher amounts when there is some type of inflammatory or infectious process occurring in the body, being one of the first signals of abnormality in the blood test.

This protein is usually used to assess the possibility of there being some type of infection or inflammatory process that is not visible, such as appendicitis, atherosclerosis, or viral and bacterial infections. However, CRP can also assess the risk of a person developing cardiovascular diseases, as if the levels are high, the risk of getting one of these diseases is also high.

The CRP test does not identify exactly which inflammation or infection the person has, but an increase in CRP levels shows that the body is fighting an aggressive agent which can also reflect on the level of leukocytes in the blood test. Since there may be different variables at play, CRP test results should always be analyzed by the doctor who prescribed the test.

C-Reactive Protein (CPR) Test: What Is It & High Levels

Normal CRP levels

The reference value for CRP levels, for both men and women, is up to 3.0 mg/L or 0.3 mg/dL. In relation to cardiovascular risk, the intervals that indicate the probability of developing a heart disease are:

  • High risk: above 3.0 mg/L;
  • Medium risk: between 1.0 and 3.0 mg/L;
  • Low risk: less than 1.0 mg/L.

It's important for the C-reactive protein levels to be between 1 and 3 mg/L. Low levels of CRP can also be seen in some cases, such as people who have undergone great weight loss, people who do a lot of physical activity, people who consume a lot of alcoholic drinks and those who use certain types of medication. It is therefore important for a doctor to identify the cause.

The CRP test results should always be interpreted by a doctor, as it's important that the tests be analyzed together in order to get to an accurate diagnosis and so as to identify the cause for CRP increase or decrease.

What is high-sensitivity CRP (hs-CRP) test 

The high-sensitivity CRP (hs-CRP) test is prescribed when the doctor wants to assess the person's risk of developing cardiovascular problems, such as heart attack or stroke. In this case, the test is requested when the person is healthy, and doesn't have any symptoms or apparent infection. This exam is more specific, and it can detect very small amounts of CRP in the blood.

If someone is apparently healthy and presents high CRP levels, this means that this person has a higher risk of developing peripheral artery disease, or having a heart attack or a stroke. In this cases, it's usually recommended to start a healthy diet and practice regular physical activity, in order to improve cardiacvascular health.

What causes high CRP levels

High levels of C-reactive protein normally occur when there is some type of inflammatory or infectious processes occurring in the body.

In some cases, the CRP amounts can indicate the gravity of the inflammation or infection:

  • Between 3.0 to 10.0 mg/L: generally indicate slight inflammation or slight infection like gingivitis, flu or cold;
  • Between 10,0 to 40,0 mg/L: can be a sign of a moderate infection, such as chickenpox or respiratory infection;
  • More than 40 mg/L: generally indicate a more serious bacterial infection;
  • More than 200 mg/L:  may indicate septicemia, a very serious situation that can be life threatening.

An increase in CRP levels can also signal chronic disease and so the doctor may prescribe other exams to evaluate what could be causing the CRP levels to increase.

What to do when the CRP is high 

After confirming high levels of CRP, the doctor will assess the results of other prescribed tests, as well as assessing the patient, taking into account the symptoms. From the moment the cause is identified, treatment can be started in a more directed and specific way.

When the patient shows signs of malaise without there being another symptom or specific risk factors, the doctor may request other exams, such as blood tumor marker tests or a CT scan, to check if increased levels of CRP are related to cancer.

When CRP levels are above 200 mg/L and the infection diagnosis is confirmed, normally the person will be hospitalized to get intravenous antibiotics. The CRP levels start to increase 6 hours after any infection starts and tend to lower after intake of antibiotics. If CRP levels have not decreased after two days, it's important that the doctor establish another treatment strategy.

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  • NURSHAD, Ali. Elevated level of C‐reactive protein may be an early marker to predict risk for severity of COVID‐19. Journal of Medical Virology. 2020
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