The C-Reactive Protein (CRP) test is a valuable blood test that measures the level of inflammation in your body. As one of the most commonly used markers for detecting inflammation, CRP testing plays an important role in diagnosing and monitoring a wide range of health conditions. This guide will help you understand what CRP is, why the test is performed, and how to interpret your results.
What is C-Reactive Protein?
C-Reactive Protein is a substance produced by your liver in response to inflammation. When your body experiences infection, injury, or chronic disease, inflammation occurs as part of your immune system's natural defence mechanism. During this inflammatory response, CRP levels in your blood can rise dramatically – sometimes increasing by a thousandfold within hours of an inflammatory trigger.
CRP is classified as an "acute phase reactant," meaning it responds quickly to inflammation. This rapid response makes it an excellent marker for detecting both acute conditions (like infections) and chronic inflammatory states (like autoimmune diseases or cardiovascular risk).
Why is a CRP Test Performed?
Healthcare providers may request a CRP test for several reasons:
Detecting Infection
CRP levels rise rapidly in response to bacterial infections, making it useful for distinguishing between bacterial and viral infections. Bacterial infections typically cause much higher CRP elevations than viral infections.
Monitoring Inflammatory Conditions
For people with chronic inflammatory conditions such as rheumatoid arthritis, lupus, or inflammatory bowel disease, regular CRP testing helps monitor disease activity and treatment effectiveness.
Assessing Cardiovascular Risk
Research has shown that chronic low-grade inflammation plays a role in the development of cardiovascular disease. A high-sensitivity CRP (hs-CRP) test can help assess your risk of heart attack and stroke, even when cholesterol levels are normal. For more information about heart health markers, read our guide on cholesterol testing.
Post-Surgery Monitoring
After surgery, CRP levels naturally rise as part of the healing process. Monitoring these levels helps healthcare providers detect potential complications such as infection.
Investigating Unexplained Symptoms
When patients present with fever, fatigue, or other symptoms that could indicate inflammation, a CRP test can help guide further investigation.
Types of CRP Tests
There are two main types of CRP tests:
Standard CRP Test
This test measures CRP levels across a wide range and is typically used to detect significant inflammation caused by infections, autoimmune conditions, or other acute illnesses. Standard CRP tests can detect levels from about 10 to 1000 mg/L.
High-Sensitivity CRP (hs-CRP) Test
This more sensitive version of the test can detect very low levels of CRP in the blood – typically between 0.5 and 10 mg/L. The hs-CRP test is primarily used to assess cardiovascular disease risk, as even slightly elevated CRP levels have been linked to increased risk of heart problems.
The CRP Test Procedure
A CRP test is a simple blood test that requires minimal preparation. Here is what you can expect:
Before the Test
In most cases, no special preparation is needed for a standard CRP test. However, if you are having an hs-CRP test for cardiovascular risk assessment, your healthcare provider may ask you to fast for 9-12 hours beforehand, as this test is often performed alongside a lipid panel.
It is worth noting that certain factors can temporarily affect CRP levels:
Inform your healthcare provider about any of these factors, as they may influence the interpretation of your results.
During the Test
The blood draw is straightforward and takes just a few minutes. A healthcare professional will clean an area on your arm (usually the inside of your elbow), insert a small needle into a vein, and collect a blood sample into a tube. You may feel a brief pinch when the needle is inserted. For more details about what to expect during a blood test, see our comprehensive guide on blood testing procedures and results.
After the Test
Once the sample is collected, a small plaster is applied to the puncture site. You can resume normal activities immediately. The sample is sent to a laboratory for analysis, and results are typically available within 24-48 hours.
Understanding Your CRP Results
CRP is measured in milligrams per litre (mg/L). The interpretation of your results depends on which type of test was performed and the clinical context.
Standard CRP Test Results:
High-Sensitivity CRP (hs-CRP) Results for Cardiovascular Risk:
It is important to note that CRP is a non-specific marker – elevated levels indicate that inflammation is present somewhere in the body but do not pinpoint the exact cause or location. Further testing is usually needed to determine the underlying condition.
What Can Cause Elevated CRP Levels?
Many conditions can cause CRP levels to rise:
Acute Causes:
Chronic Causes:
CRP and Cardiovascular Health
The link between inflammation and heart disease has been well established. Chronic low-grade inflammation can damage the walls of blood vessels, contributing to the development of atherosclerosis (the buildup of fatty plaques in arteries). Studies have shown that elevated hs-CRP levels are associated with increased risk of:
For individuals with intermediate cardiovascular risk based on traditional factors (age, blood pressure, cholesterol, smoking status), hs-CRP testing can provide additional information to guide preventive strategies. If you are interested in a comprehensive assessment of your heart health, consider our health screening packages which include both CRP and lipid profile testing.
Lowering Your CRP Levels
If your CRP levels are elevated due to chronic inflammation or cardiovascular risk, lifestyle modifications can help:
In some cases, medications such as statins may be prescribed to help lower both cholesterol and CRP levels.
When to Seek Medical Advice
At Private Blood Tests London, we provide your raw CRP test data. We recommend sharing your results with your GP or healthcare provider for proper interpretation, particularly if:
Book Your CRP Test Today
Understanding your inflammation levels is an important part of managing your overall health. At Private Blood Tests London, we offer CRP testing at our CQC-registered clinic in South Kensington. Our experienced nursing team ensures a comfortable testing experience, and your results are delivered quickly and securely.
Learn about [how blood tests reveal early signs of heart disease](/blog/how-blood-tests-can-reveal-early-signs-of-heart-disease) and explore our [health screening packages](/health-screening).
Whether you are investigating symptoms, monitoring a chronic condition, or assessing your cardiovascular risk, we are here to help. Book your appointment today and take a proactive step towards understanding your health.