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C-Reactive Protein (CRP)

C-Reactive Protein (CRP)

June 25, 2020

Inflammation

What is C Reactive Protein (CRP)?

C-reactive protein (CRP) is a protein produced by the liver. A small amount of CRP always circulates in our blood, but its level drastically increases in the presence of infection, inflammation and tissue injury.

Inflammation is our body’s response against harm, including infections, injuries, allergens and some toxins. When our cells are damaged, they release chemical signals that activate our immune system. Depending on how long the immune system is activated, an inflammatory process can be acute or chronic.

Acute inflammation is crucial for our survival as it helps us fight infections and heal wounds. However, an acute inflammation can sometimes linger on and become a chronic inflammation, which can have a more negative impact on our health.

A chronic inflammation can be due to an unresolved acute inflammation or a so-called “autoimmune process”, where our immune system mistakenly attacks our own healthy tissue. Long-term exposure to environmental irritants, such as cigarette smoke or air pollution also causes chronic inflammation.

CRP levels in the blood usually rise to its peak 36-50 hours following an infection or injury. Once the inflammation is resolved, CRP levels quickly fall back to normal due to its relatively short half-life.

Why is this analysis important?

CRP levels in the blood are usually determined when infection is suspected. In the clinic, CRP is often used to differentiate between bacterial and viral infections in a feverish patient. While bacterials infections typically cause dramatic increases in the level of CRP, viral infections typically only cause modest increases. However, not all infections fall within this pattern. For example, patients requiring hospital care for COVID-19 infections can have CRP levels higher than that of the bacterial pneumonia, despite the fact the COVID-19 is caused by a virus and not a bacteria.

Measuring the low levels of CRP that circulates in the blood in asymptomatic people with no sign of infection or injury can help evaluate the risk of cardiovascular disease such as heart attack and stroke. However, the amount of CRP that circulates the blood is so small that it cannot be detected by conventional CRP assays, but requires a special assay called “hsCRP”, which is short for “high sensitivity CRP”. Research shows that combining hsCRP with traditional cardiovascular risk assessment tests such as the lipid panel could better predict risk of cardiovascular disease than lipid panel alone.

In short, it is useful to analyse CRP levels in the blood to:

  • Identify the presence of inflammation

  • Investigate the cause of an infection

  • Monitor the progression and treatment response of inflammatory/infectious diseases

  • Assess the risk of cardiovascular diseases

Results

The reference range for CRP levels in the blood can be different depending on the laboratory and technique used. Doctors usually also take into account a number of factors when evaluating CRP values.

High CRP levels in the blood may be associated with:

  • Infections

  • Trauma and tissue injury

  • Wound healing and after surgery

  • Autoimmune diseases

  • Tumor processes

  • Chronic diseases such as diabetes, peripheral vascular disease or cardiovascular disease

  • Pregnancy

  • Smoking

  • Sedentary lifestyle

Low CRP levels in the blood may be associated with:

  • Liver failure

Other considerations

Increased CRP levels only indicate the presence of inflammation but cannot pinpoint the exact cause. To identify the cause of inflammation, further investigation by a doctor is required.

Normal CRP levels cannot completely rule out inflammation. A CRP value should be evaluated together with other markers of inflammation such as ESR, white blood cells and ferritin.

Slight increase in CRP during pregnancy, especially late pregnancy is normal and usually not a sign of any infection. However, if symptoms of infection are present, a doctor should be consulted.

References

Acute phase reactants. Irving Kushner, MD. UpToDate Mar 01, 2019.

Comparison of C-reactive protein and low-density lipoprotein cholesterol levels in the prediction of first cardiovascular events. Paul M Ridker , Nader Rifai, Lynda Rose, Julie E Buring, Nancy R Cook. New England Journal of Medicine. 2002 Nov 14;347(20):1557-65.