CRP Blood Test: How It Works and What Do the Results Mean?

What is a C reactive protein (CRP) blood test?

A CRP blood test is used to measure the level of C reactive protein inside the blood. This protein is released by the liver into the bloodstream in response to inflammation caused by infections, injuries, or chronic conditions.

However, even though the CRP test can detect the presence of inflammation, it can’t identify the exact cause or where it is in your body. Because of this, your healthcare provider may perform additional tests, such as erythrocyte sedimentation rate (ESR), to help diagnose the underlying medical condition.

What conditions can the CRP blood test detect?

The CRP test can be used by healthcare providers to detect inflammation in the body, monitor existing chronic or inflammatory conditions, and assess the effectiveness of your current treatment. Here are some conditions that the C reactive protein test can detect, including:

• Bacterial or viral infections, such as urinary tract infection (UTI).

• Fungal infections, such as chromoblastomycosis (chronic skin infection).

• Lung diseases, such as asthma or bronchitis.

• Autoimmune diseases, such as lupus or coeliac disease.

• Chronic conditions, such as rheumatoid arthritis.

• Inflammatory bowel disease (IBD), which is an inflammation in the gastrointestinal tract that's commonly caused by Crohn's disease or ulcerative colitis.

A different type of the CRP blood test, called the high-sensitivity CRP (hs-CRP) test, can also be used to measure the risk of heart disease in addition to finding the above inflammatory conditions. To provide a more comprehensive evaluation of cardiovascular risk, the hs-CRP test is usually performed in conjunction with additional health screenings, such as cholesterol levels and blood pressure. 

When do I need a CRP test?

Your healthcare provider may order a CRP test if you are showing symptoms associated with inflammation in the body, such as:

• Unexplained fever

• Rapid breathing (tachypnea)

• Rapid heart rate (tachycardia)

• Nausea and vomiting

• Unexplained weight loss

• Joint stiffness

• Neck or shoulder pain

• Headaches

After your healthcare provider has confirmed the presence of inflammatory activity within the body, they can proceed with other clinical assessments to further diagnose your medical condition.

If you're experiencing any of the symptoms mentioned above, request an appointment with Thomson Medical. Our specialists can assist with further diagnoses and provide a personalised recommendation.

What to expect during a CRP blood test

The CRP blood test is a simple procedure that usually requires no special preparation. Your healthcare provider only needs to take a small amount of blood from a vein in your arm.

Before inserting the needle to draw your blood, the puncture area will be sterilised with an antiseptic to prevent infection. The needle is then inserted into your vein to collect it in a blood vial, the entire procedure usually takes less than five minutes. Once the sample is collected, the needle is removed, and a piece of gauze and a bandage will be placed over the puncture site. Thereafter, your blood sample is sent to a lab for analysis. Your results will usually be available within a few days.

What do the results mean?

Currently, there's no set reference values for CRP blood levels, so different labs may have slightly different reference ranges. The results of your CRP blood test are usually measured in milligrams per decilitre (mg/dL). However, as a general rule, these are the classification levels for CRP:

In general, healthy adults have low CRP levels (less than 0.3 mg/dL), with increases up to 1 mg/dL still considered within the normal range. If your CRP results are higher than these standard ranges, it indicates elevated levels of inflammation in the body and may warrant further investigation.

If your CRP levels are elevated, don't hesitate to consult a doctor. Request an appointment with Thomson Medical for recommendations based on your medical conditions and further evaluation.

Hs-CRP test results

In addition to standard CRP testing, a high-sensitivity C-reactive protein (hs-CRP) test can help assess the risk of future cardiovascular disease (CVD). This includes conditions like heart attacks and strokes, even in individuals with no prior history of heart disease.

The results are measured in milligrams per litre (mg/L) and are interpreted as follows:

• An hs-CRP level below 1.0 mg/L indicates a low risk of cardiovascular disease.

• An hs-CRP level between 1.0 and 3.0 mg/L can suggest a moderate risk of cardiovascular disease.

• An hs-CRP level above 3.0 mg/L indicates a high risk of cardiovascular disease.

Because the CRP levels can vary due to factors like a cold or smoking, it's recommended to repeat the hs-CRP test at least two weeks apart to confirm results and ensure accuracy.

Are there any risks to the test?

Since the CRP blood test only requires a sample of your blood to check the level of inflammation, it is a low-risk test. However, as this test involves drawing blood directly from your vein, there are some minor discomforts you may experience, such as:

• Slight bruising, swelling, or soreness at the puncture site.

• Slight pain or discomfort around the area where the needle was inserted.

• There might be a slight sting during the needle insertion or removal process.

• Dizziness due to the withdrawal of blood.

Staying hydrated by drinking plain water before your blood test can keep your veins fuller, making it easier for the medical professional to draw your blood, potentially reducing the discomfort you may experience during the test.

FAQ

What does it mean when the CRP blood test is high?

A high CRP level indicates active inflammation in the body, which may result from conditions such as autoimmune diseases or bacterial infections. However, since this test doesn't specify the exact cause of the inflammation, it's usually performed alongside other blood tests for a more accurate diagnosis.

What infections cause high CRP?

When an infection occurs, the body responds with an inflammatory reaction to help fight off the germs. This natural reaction causes CRP levels to spike and usually tends to be higher in bacterial infections than in viral infections.

Here are some infections that can lead to elevated CRP levels, including:

• Bacterial infections

  • Conditions such as pneumonia, pelvic inflammatory disease, sepsis, and tuberculosis can cause significant inflammation and raise CRP levels.

• Viral infections

  • Illnesses like flu (influenza), COVID-19, or viral gastroenteritis can also lead to inflammation.

• Fungal infections

  • Although rare, certain fungal infections, such as chromoblastomycosis (a chronic skin infection), can lead to elevated CRP levels.

How do I reduce my CRP levels?

To lower your CRP levels, it usually means addressing the medical or chronic condition that causes the inflammation. Here are some treatments you can try to reduce CRP levels, such as:

• Exercise regularly to maintain an ideal body weight.

• Quit smoking and drinking alcohol.

• Eat a healthy, nutritionally balanced diet rich in antioxidants and omega-3 fatty acids.

• Consume anti-inflammatory medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs) or corticosteroids.

What foods should you avoid if you have high CRP?

If your CRP test results are high, you should avoid foods that can trigger inflammation. The condition can be triggered due to the composition of these foods and how the body processes them. Here are some foods you should avoid if you have high CRP levels, such as:

• Refined carbohydrates, like white bread, white rice, pastries, and other processed carbs.

• Foods and drinks with added sugar, such as soda, cookies, sweets, and coffee or tea drinks.

• Processed meat, such as bacon, hot dogs, sausage, and corned beef.

• Deep-fried food, such as french fries, fried chicken, and doughnuts.

• Foods high in saturated and trans fats, which are contained in fast foods, processed snacks, and margarines.

What is an alarming CRP level?

A CRP blood test result that exceeds 50 mg/dL is considered alarming. This is because it indicates the presence of an acute bacterial infection that necessitates immediate medical attention.

The information provided is intended for general guidance only and should not be considered medical advice. For personalised recommendations and tailored advice from a specialist, request an appointment at Thomson Medical.