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What type of marker is CRP?

C-reactive protein (CRP) is an important inflammatory marker that is often measured in medical testing. Understanding what type of marker CRP is and how it functions in the body can provide useful health insights.

What is CRP?

CRP is a protein made by the liver that circulates in the bloodstream. When there is inflammation in the body, CRP levels rise rapidly. This makes CRP a valuable marker of inflammation.

Inflammation is the body’s response to infection, injury, or cellular damage. During inflammation, the immune system releases special proteins called cytokines that trigger the liver to produce more CRP. The more inflammation present, the higher CRP levels climb.

Because of this relationship with inflammation, measuring CRP levels in the blood can reveal important health information. Abnormal CRP levels may indicate the presence of infection, autoimmune disorders, cardiovascular disease risk, and more.

Key Facts About CRP:

  • CRP is produced by the liver and released into the bloodstream.
  • CRP levels rise rapidly when inflammation is present.
  • Higher CRP indicates more inflammation in the body.
  • Checking CRP levels can help detect infection, injury, and disease.
  • CRP is considered an acute phase reactant protein.

CRP as an Acute Phase Reactant

CRP is classified as an acute phase reactant protein. Acute phase reactants are a group of proteins whose concentrations increase or decrease significantly during inflammation and infection.

In addition to CRP, other major acute phase reactants include:

  • Fibrinogen
  • Serum amyloid A
  • Ferritin
  • Procalcitonin

These proteins are synthesized in the liver and released into the blood within hours of tissue injury or the start of an inflammatory process. Their levels can increase as much as 1000% during inflammation.

By testing for changes in acute phase reactants, doctors can detect the presence of inflammation, even before outward symptoms appear. This allows for faster diagnosis and treatment.

How CRP Levels Change During Inflammation

Here is an overview of how CRP levels typically change during the inflammatory response:

  • Baseline: At healthy baseline, CRP levels are normally below 10 mg/L.
  • Early Rise: Within 6 hours of an inflammatory trigger, CRP levels begin rising.
  • Peak: CRP levels peak at around 48 hours, often increasing over 100-fold.
  • Decline: If inflammation resolves, CRP drops back to normal over the next 6-8 days.
  • Chronic Inflammation: With ongoing inflammation, CRP remains persistently elevated.

This pattern makes CRP useful for diagnosing and monitoring inflammatory conditions. A single CRP test can reveal if inflammation is present. And repeating the test over time can show if inflammation is improving or worsening.

Normal, Borderline, and High CRP Levels

Here is how CRP levels are typically interpreted:

CRP Level Interpretation
Less than 1.0 mg/L Normal: Lowest risk for cardiovascular disease
1.0 – 3.0 mg/L Normal to slightly elevated: Average CVD risk
3.1 – 10 mg/L Borderline high: Moderate CVD risk
Greater than 10 mg/L High: Highest CVD risk

For identifying inflammation from injury or infection, a CRP over 10 mg/L is considered high.

Functions of CRP

CRP has several important functions, including:

  • Binding to damaged cells and microbes – CRP recognizes foreign pathogens and dead or dying cells. It flags them for removal by binding to them.
  • Activating complement – CRP interacts with the complement system, part of the innate immune response. This enhances inflammation and recruits immune cells.
  • Promoting phagocytosis – CRP makes it easier for phagocytes like macrophages to engulf and destroy bacteria and other cellular debris.
  • Stimulating cytokine release – CRP promotes cytokine secretion to amplify the inflammatory signal.

Through these mechanisms, CRP plays a key role in the inflammatory process and immune function. Measuring CRP levels provides insight into how much inflammation-related activity is occurring in the body.

Causes of High CRP

Some common causes of elevated CRP include:

  • Bacterial infections – Elevated CRP is a sign of active bacterial infection. Levels may be markedly high with sepsis.
  • Viral infections – Viral illnesses can also raise CRP, though the increase is usually more modest.
  • Inflammatory conditions – Diseases like rheumatoid arthritis, lupus, and inflammatory bowel disease raise CRP.
  • Tissue damage or trauma – Any injury, burns, or tissue necrosis activates inflammation and CRP release.
  • Heart attack and stroke – CRP rises with the artery damage and inflammation of heart attacks and strokes.
  • Cancer – Many cancers increase CRP levels, particularly blood cancers.

In the absence of infection or injury, chronic inflammation within the body can also lead to persistently elevated CRP levels over time.

Medical Uses of CRP Testing

Measuring CRP is a common medical test with many uses, including:

  • Detecting infection – CRP can identify bacterial infections and sepsis rapidly.
  • Monitoring inflammatory disease – For conditions like rheumatoid arthritis, CRP reflects disease activity and severity.
  • Predicting cardiovascular risk – Those with high CRP have elevated risk of heart attack, stroke, and peripheral artery disease.
  • Evaluating treatment response – Falling CRP indicates a treatment is working and inflammation is resolving.
  • Distinguishing viral vs. bacterial infection – Viral illnesses tend to cause lower CRP elevations than bacterial ones.
  • Predicting complications – Higher CRP predicts worse prognosis and more complications after major trauma or surgery.

Checking CRP is inexpensive and the test is often repeated over time to monitor disease progression and treatment efficacy. It provides an objective measure of inflammation throughout the body.

High Sensitivity CRP Test

A high sensitivity CRP (hs-CRP) test can detect CRP levels in the low normal range, less than 10 mg/L. The regular CRP test often cannot reliably detect CRP below 10 mg/L.

The hs-CRP test is used to assess cardiovascular disease risk. Those with CRP between 1-3 mg/L have moderately increased risk while CRP above 3 mg/L indicates high risk.

Hs-CRP can detect even minor inflammation within blood vessels early on, allowing steps to be taken to prevent progression to cardiovascular disease.

Limitations of CRP Testing

While CRP is an important marker of inflammation, there are some limitations to be aware of:

  • CRP is nonspecific – it cannot identify the exact cause of inflammation.
  • Levels may be elevated due to unrelated factors like obesity, smoking, aging, etc.
  • CRP may be normal in some cases of infection or inflammation.
  • Testing must be combined with clinical evaluation and other labs for accuracy.

CRP should not be relied on in isolation. Doctors must interpret CRP results in combination with a patient’s full clinical presentation.

Takeaways About CRP

  • CRP is an acute phase reactant protein made by the liver that circulates in blood plasma.
  • CRP levels rise rapidly during inflammatory processes in the body.
  • Checking CRP is useful for detecting and monitoring infection, inflammatory disease activity, heart disease risk, and more.
  • CRP testing has some limitations but can provide objective data about systemic inflammation when interpreted carefully.

By understanding what type of biomarker CRP is and how it behaves, doctors can appropriately utilize CRP testing to gain valuable clinical insights and guide patient care decisions.

In summary, CRP is a helpful, widely used inflammatory marker that aids in the diagnosis, treatment, and monitoring of inflammatory conditions when applied properly in medical practice.