What is C-Reactive Protein (CRP)?
C-Reactive Protein (CRP) is a special type of protein made by the liver that increases in the blood whenever there is inflammation, infection, or tissue injury in the body. The test doesn’t show the exact cause of inflammation but acts as a sensitive indicator of its presence and severity.
Doctors commonly use the CRP test to identify acute or chronic inflammation, monitor treatment response, and evaluate the risk of heart-related diseases.
Where is CRP Produced in the Body?
CRP is produced by the liver when the immune system releases specific chemical messengers known as cytokines, mainly interleukin-6 (IL-6), during infection or inflammation.
When body tissues are injured or invaded by harmful bacteria or viruses, IL-6 signals the liver to release CRP into the bloodstream. The higher the inflammation, the more CRP is released — which is why it is a reliable marker in blood tests.
Main Functions and Importance of CRP
CRP plays an important role in the body’s immune defense system. Here are its key functions and uses:
- Early detection of inflammation: CRP acts as an early warning sign for infections or inflammatory diseases even before symptoms become severe.
- Helps activate the complement system: CRP binds to damaged cells and certain bacteria, helping the immune system remove them effectively.
- Monitoring treatment response: Doctors use CRP levels to check how well a patient is recovering from infections or autoimmune conditions.
- Heart disease indicator: Mildly raised CRP levels may indicate a higher risk of cardiovascular diseases like heart attack or atherosclerosis.
Thus, the CRP test is useful not only for identifying infections but also for long-term disease monitoring.
Causes of Low or Negative CRP Levels
Low or undetectable CRP levels are generally a good sign, showing that the body has no ongoing inflammation or infection.
Common causes include:
- Being in a normal healthy state.
- Recovery after a recent infection or surgery.
- Successful response to anti-inflammatory or antibiotic treatment.
Symptoms of Low or Negative CRP Levels
There are usually no symptoms linked with low or negative CRP levels because they simply represent absence of active inflammation. A person with normal CRP levels is typically healthy.
Causes of High or Positive CRP Levels
When CRP levels are high, it signals the body is responding to inflammation, infection, or injury. Common causes include:
- Acute bacterial or viral infections (like pneumonia or sepsis).
- Autoimmune disorders such as rheumatoid arthritis or lupus (SLE).
- Chronic inflammatory diseases, for example inflammatory bowel disease (IBD).
- Tissue damage, burns, or after major surgery.
- Heart-related conditions, such as atherosclerosis or heart attack.
- Certain cancers, which cause persistent inflammation in the body.
Symptoms of High or Positive CRP Levels
CRP itself does not cause any symptoms; rather, the symptoms depend on the underlying condition that triggered inflammation. Common signs may include:
- Fever, fatigue, and weakness due to infection or inflammation.
- Pain, redness, or swelling at an affected area (for example, in infections or injury).
- Joint pain and stiffness in autoimmune diseases like arthritis.
- Chest pain or shortness of breath in cardiovascular diseases.
If you experience these symptoms, your doctor may recommend a CRP test to check for inflammation or infection.
CRP Test Reference Ranges
| CRP Level (mg/L) | Interpretation |
|---|---|
| < 1 mg/L | Normal or low cardiovascular risk |
| 1–3 mg/L | Average cardiovascular risk or mild inflammation |
| > 3 mg/L | High cardiovascular risk or active inflammation |
| > 100 mg/L | Severe infection or acute inflammation |
These ranges may slightly vary between laboratories. Very high values (above 100 mg/L) usually suggest a serious bacterial infection or major inflammatory condition.
Types of CRP Tests
There are two types of CRP tests used in clinical practice:
- Standard CRP Test: Measures high levels of CRP, useful for detecting infections and inflammatory diseases.
- High-Sensitivity CRP (hs-CRP) Test: Detects very small CRP changes to assess heart disease risk. Even a slight rise may indicate possible inflammation in blood vessels.
Sample Type for CRP Test
A blood sample (serum or plasma) is collected from a vein in the arm using a sterile needle.
No special preparation is needed, but you should inform your doctor about any medications you are taking, as some drugs (like statins or anti-inflammatory medicines) can affect CRP levels.
Test Preparation
- No fasting or dietary restrictions are usually required.
- Inform the doctor about ongoing infections, recent surgeries, or inflammatory conditions, as these can increase CRP.
- Avoid strenuous exercise before the test since intense activity can temporarily raise CRP levels.
- For heart risk assessment (hs-CRP test), ensure the test is done when you’re free of any infection to avoid false results.
When to Consult a Doctor
You should consult a doctor if:
- You have unexplained fever, fatigue, or inflammation that doesn’t improve.
- You suffer from joint pain, swelling, or stiffness.
- Your CRP levels remain high even after treatment.
- You have a family history of heart disease or your hs-CRP test result shows an elevated risk.
The doctor will interpret CRP levels along with other test results and medical history to find the root cause.
Important Word Explanations
- Inflammation: The body’s reaction to injury or infection, causing redness, swelling, or pain.
- Interleukin-6 (IL-6): A signaling protein that stimulates the liver to produce CRP.
- Autoimmune Disease: A condition in which the immune system mistakenly attacks healthy body tissues.
- Atherosclerosis: Hardening and narrowing of arteries due to fat and cholesterol buildup.
- High-Sensitivity CRP (hs-CRP): A more precise test used for predicting heart disease risk.
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