C-Reactive Protein

What is an C-Reactive Protein Test?

A C-reactive protein (CRP) test is a blood test that measures the level of C-reactive protein in your bloodstream. CRP is a protein produced by the liver in response to inflammation. It is a valuable marker of inflammation and is commonly used by healthcare professionals to assess the presence and severity of inflammation in various medical conditions.

The CRP test is a simple and quick diagnostic tool that can help doctors in several ways. It is often used to monitor inflammatory conditions, detect infections,  and assess cardiovascular risks. It can also be used to guide treatment planning and screen for autoimmune disorders.

The CRP test uses a blood sample to diagnose and manage medical conditions. Elevated CRP levels indicate inflammation, but further tests and evaluation are needed to determine the exact cause and treatment approach.

How Does it Work?

Step 1: Sample Collection

A healthcare provider will prepare for the CRP test by selecting an appropriate vein, usually in the arm, and cleaning the area with an antiseptic. They will then insert a needle into the vein and collect a small amount of blood into a special tube or vial.

Step 2: Laboratory Analysis

The collected blood sample is sent to a laboratory for analysis. In the lab, a technician will centrifuge the sample to separate the liquid (serum or plasma) from the blood cells.

Step 3: CRP Measurement

The separated serum or plasma is then tested using immunoturbidimetry or a high-sensitivity CRP (hs-CRP) assay. In immunoturbidimetry, a specific antibody reacts with CRP in the sample, causing it to clump together and change the sample's turbidity. The degree of turbidity is proportional to the CRP concentration. The hs-CRP assay uses more sensitive techniques to measure lower levels of CRP, which is particularly useful for assessing cardiovascular risk.

Step 4: Reporting Results

The laboratory provides a report indicating the blood's CRP level in milligrams per liter (mg/L) or milligrams per deciliter (mg/dL). This result is typically sent to the healthcare provider who ordered the test.

Step 5: Interpretation

The healthcare provider interprets the CRP level in the context of the patient's medical history and symptoms. Elevated CRP levels may suggest inflammation in the body, but the specific cause and severity of the inflammation require further evaluation.

The CRP test is not a definitive diagnosis tool but plays a vital role in understanding inflammation's underlying cause. You can get the test request form from your healthcare provider or laboratory, but it's essential to consult your doctor before taking the test. They will provide you with the necessary forms and instructions for sample collection.

When Would you use this Test?

The C-reactive protein (CRP) test is a valuable tool used by healthcare practitioners across various medical specialties to assess inflammation in the body. Here are several situations in which this test is commonly used:

• Infectious Diseases: Physicians often employ the CRP test to detect and monitor infections. Elevated CRP levels can indicate the presence of bacterial or viral infections, helping doctors determine the appropriate treatment regimen and track the effectiveness of antibiotics or antiviral medications.
• Rheumatology: Rheumatologists use the CRP test to diagnose and monitor inflammatory autoimmune conditions like rheumatoid arthritis and systemic lupus erythematosus. It assists in assessing disease activity and guiding treatment decisions.
• Cardiology: Cardiologists use the CRP test to assess cardiovascular risk. Elevated CRP levels are associated with a higher risk of heart disease and may prompt further evaluation and preventive measures, such as lifestyle changes or medications.
• Gastroenterology: Gastroenterologists may utilize the CRP test to diagnose and monitor inflammatory bowel diseases (IBD) like Crohn's disease and ulcerative colitis. Changes in CRP levels can indicate disease flares or remission.
• Orthopedics: Orthopedic surgeons may order CRP tests before and after joint replacement surgeries. Elevated postoperative CRP levels can suggest complications like infection while decreasing levels indicate successful recovery.
• Primary Care: General practitioners and internists use the CRP test as a general marker of inflammation in various health conditions, aiding the diagnostic process and monitoring treatment effectiveness.
• Emergency Medicine: In emergency settings, the CRP test can help identify patients with severe infections or inflammatory conditions requiring immediate attention.
• Pediatrics: Pediatricians may order CRP tests to evaluate children with suspected infections, inflammatory conditions, or chronic diseases like juvenile idiopathic arthritis.
• Preventive Medicine: Some practitioners use the CRP test as part of preventative health screenings to assess overall inflammation and potential cardiovascular risk in asymptomatic individuals.

What do the Results Mean?

Interpreting C-reactive protein (CRP) test results is crucial for healthcare providers to understand the presence and severity of inflammation in a patient's body. CRP levels are measured in milligrams per liter (mg/L) or milligrams per deciliter (mg/dL) of blood. Here's what common CRP test results typically mean:

• Low or Normal CRP (0-1 mg/L): A low CRP level suggests no significant ongoing inflammation in the body. This is typically seen in healthy individuals or those with well-controlled chronic conditions.
• Moderate CRP (1-10 mg/L): Moderate CRP levels may indicate mild inflammation. This can be due to minor infections, allergies, or chronic conditions with low-grade inflammation like osteoarthritis.
• High CRP (>10 mg/L): Elevated CRP levels, significantly above 10 mg/L, often signify significant inflammation. Possible causes include severe infections, autoimmune diseases (e.g., rheumatoid arthritis, lupus), inflammatory bowel disease (e.g., Crohn's disease), or acute injuries.
• Very High CRP (>100 mg/L): Extremely elevated CRP levels are typically seen in acute and severe inflammatory conditions, such as severe infections (sepsis), extensive tissue damage, or certain autoimmune diseases during acute flares.

In some cases, healthcare providers may also use a high-sensitivity CRP (hs-CRP) test, which can detect even lower levels of CRP and is often used to assess cardiovascular risk. For this test:

• Low hs-CRP (<1 mg/L): Low levels are associated with a lower risk of cardiovascular disease.
• Moderate hs-CRP (1-3 mg/L): Moderate levels indicate a moderate risk of cardiovascular disease.
• High hs-CRP (>3 mg/L): High levels suggest an increased risk of cardiovascular disease, potentially indicating underlying inflammation in blood vessels.

CRP levels can indicate inflammation, but a healthcare provider must evaluate the underlying cause and treatment plan. Consult a healthcare professional for personalized guidance and interpretation of your CRP test results.

Research & Evidence

The C-reactive protein (CRP) test has a well-established history in medicine, with extensive research and evidence supporting its use as a valuable diagnostic and prognostic tool for assessing inflammation. 

CRP was first discovered in 1930 by scientists Tillet and Francis when they identified it as a substance in the serum of patients with acute inflammation that reacted with the C-polysaccharide of Streptococcus pneumoniae. In the following decades, research continued, and the CRP test became a marker of inflammation in various medical conditions.

In recent years, the development of high-sensitivity CRP (hs-CRP) assays has allowed for more precise measurement of lower CRP levels, particularly for assessing cardiovascular risk.

Numerous clinical studies and research papers have demonstrated the utility of the CRP test in various medical contexts. In cardiovascular medicine, research, such as the "JUPITER trial" (Justification for the Use of Statins in Prevention: An Intervention Trial Evaluating Rosuvastatin), showed that elevated CRP levels are associated with an increased risk of cardiovascular events. This led to the recognizing of hs-CRP as a valuable tool for assessing cardiovascular risk.

In rheumatology, the CRP test is routinely used to monitor disease activity in conditions like rheumatoid arthritis. Research has shown a correlation between CRP levels and the severity of joint inflammation. In infectious diseases, studies have established the CRP test's effectiveness in diagnosing and monitoring infections, as elevated CRP levels often indicate an inflammatory response to infection.

Research continues to explore the role of CRP as a biomarker in various conditions, including cancer, diabetes, and autoimmune diseases, contributing to our understanding of inflammation's role in these diseases.

References

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• Donovan, R. (2023, May 4). C-Reactive protein test. Healthline. https://www.healthline.com/health/c-reactive-protein
• Eustice, C. (2023). What is a C-Reactive protein (CRP) test? Verywell Health. https://www.verywellhealth.com/what-is-the-c-reactive-protein-crp-test-188021
• Faacc, T. K. P. D. (2022, July 29). C Reactive Protein (CRP blood test) - Testing.com. Testing.com. https://www.testing.com/tests/c-reactive-protein-crp/
• Healthdirect Australia. (n.d.). C-reactive protein (CRP) blood test. https://www.healthdirect.gov.au/c-reactive-protein-CRP-blood-test
• Huizen, J. (2023, August 22). What does it mean if you have a high C-reactive protein level? https://www.medicalnewstoday.com/articles/322138
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