A C-reactive protein (CRP) test is a blood test used to detect general inflammation. Inflammation is the body's natural response to infection, disease, or injury, so a CRP test can provide the first clue as to whether some sort of inflammatory condition is occurring.
A CRP test cannot tell what the source of the inflammation is, but, when combined with other tests such as a complete blood count (CBC), it can help narrow the possible causes.
This article walks you through the purpose and uses of the CRP test, including how it is performed and what the results mean.
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What Is C-Reactive Protein?
C-reactive protein is a protein produced by the liver that is normally found in the bloodstream at low levels. When there is any inflammatory condition in the body, the liver will release more.
The role of CRP is to activate certain parts of the immune system, specifically white blood cells called macrophages that clear foreign attackers (like bacteria) and dead or dying cells from the body.
CRP levels rise and fall in tandem with the level of inflammation in the body, making them an ideal marker of any number of inflammatory conditions.
Why Is the CRP Test Done?
The CRP test is a general marker for inflammation. It is used to determine if your symptoms are related to an inflammatory or non-inflammatory condition. The results, along with other findings, can help narrow the possible causes.
Because CRP levels are dynamic, rising and falling in tandem with inflammation, they can help determine whether the condition is acute (sudden, severe, and typically short-lasting) or chronic (persistent and often progressive).
Based on how high the CRP levels are, the lab can narrow the likely suspects. By way of example, CRP levels with acute bacterial infections will invariably be higher than with chronic autoimmune diseases like rheumatoid arthritis.
Although there are limitations to what the CRP test can reveal, it is a relatively reliable way to measure inflammation. The higher the CRP levels, the greater amount of inflammation in the body.
The CRP test can help identify a wide array of medical conditions, including:
- Allergic reactions
- Asthma
- Autoimmune diseases like rheumatoid arthritis and lupus
- Bacterial infections
- Bronchitis
- Cancer
- Celiac disease
- Chronic obstructive pulmonary disease (COPD)
- Connective tissue disease
- Diabetes
- Heart attack
- Heart disease, including atherosclerosis or myocarditis
- Hypertension (high blood pressure)
- Inflammatory bowel disease (IBD)
- Major trauma
- Pancreatitis
- Pelvic inflammatory disease (PID)
- Pneumonia
- Systemic (whole-body) fungal infections
- Vascular diseases like aortic aneurysms and vasculitis
- Viral infections
A CRP test is sometimes used to predict the progression of COVID-19. Studies have found that people with COVID-19 who have higher CRP levels have an increased chance of developing severe disease.
CRP and Heart Disease
The CRP test is increasingly used to determine a person's risk of heart attack or stroke and whether medications are needed to help lower the risk.
With heart disease, CRP levels tend to be modestly elevated and will gradually increase as the disease progresses. A test called a high-sensitivity CRP (hs-CRP) test can be used in people with risk factors for heart disease to decide whether treatment is needed.
In some cases, a CRP test can be the deciding fact even if levels are only mildly elevated.
Among the other risk factors that inform the decision to treat are:
- A family history of heart disease
- Diabetes
- High blood pressure
- High cholesterol
- Smoking
- Being overweight or having obesity
- Heavy alcohol use
- Physical inactivity
- A diet high in saturated fats and refined carbohydrates
Related Tests
The CRP test is often performed with another blood test called the erythrocyte sedimentation rate (ESR). Both are non-specific markers for inflammation but, together, can offer important clues as to what is going on in the body.
The ESR checks for inflammation by seeing how quickly red blood cells fall to the bottom of a test tube over the course of one hour. Because inflammatory chemicals produced by the body cause red blood cells to clump together, the rate at which they fall will be faster.
As such, an ESR is an indirect measure of inflammation while a CRP is a direct measure of inflammation.
The main difference between the two tests is that changes occur more quickly with CRP. For instance, CRP may drop quickly once an infection has cleared, while ESR will remain elevated. In such cases, the ESR can reveal that you had an illness even if the CRP shows nothing.
What Is a High C-Reactive Protein Level?
The CRP test result is typically reported in milligrams per liter (mg/L).
Based on your CRP levels, a doctor can begin to narrow down the possible causes of an illness. Some of the likely causes can be broken down by the following CRP results:
| CRP Level | Classification | Possible Meaning |
|---|---|---|
| Under 3 mg/L | Normal | Normal |
| 3 to 10 mg/L | Normal to moderate elevation | Obese Pregnancy Smoking Diabetes Gum disease Common cold |
| 10 to 100 mg/L | Whole-body inflammation | Rheumatoid arthritis Lupus Pancreatitis Acute bronchitis Cancer |
| Over 100 mg/L | Marked whole-body inflammation | Acute bacterial infection Viral infection Systemic vasculitis Major trauma |
| Over 500 mg/L | Severe whole-body inflammation | Severe bacterial infection Sepsis |
hs-CRP Test
The results of the hs-CRP test are classified as follows to offer a sense of one's risk of a heart attack or stroke:
- Low risk: Lower than 1.0 mg/L
- Average risk: 1.0 and 3.0 mg/L
- High risk: Above 3.0 mg/L
Risks of the Tests
There are very few risks involved with blood tests. You may experience bruising, swelling, or a hematoma (a pooling of blood under the skin) after the blood draw.
Some people feel dizzy, lightheaded, or even faint. And there is a very small risk of infection from the needle puncture.
How to Prepare for the Test
Before getting a CRP test, let your healthcare provider know about any medications you take since some can affect CRP levels.
Location and Timing
The CRP test can be performed in your doctor's office, at a local hospital or clinic, or at a dedicated lab facility.
A blood draw usually takes less than five minutes. You will be able to leave as soon as the test is complete as long as you're not feeling faint or sick.
What to Wear
It is helpful to wear a short-sleeved shirt for the blood draw. Avoid tight sleeves that are difficult to roll or push up.
Food and Drink
A CRP test doesn't require fasting beforehand. However, other blood tests may be performed at the same time that do, such as a fasting cholesterol test. Speak with your healthcare provider or the lab to double-check.
Cost and Health Insurance
A CRP test is relatively inexpensive—around $12 to $16, on average. If you have health insurance, your plan should cover the cost at least in part.
You can find out what your out-of-pocket costs are by calling the number on the back of your insurance card.
What to Bring
Bring a form of ID (such as your driver's license) as well as your insurance card and an approved form of payment, if needed. Check with the lab in advance to find out what kinds of payment they accept.
What to Expect During the Test
The CRP test may be performed by a lab technician, a nurse, or a phlebotomist, a professional who is specially trained to draw blood.
Pre-Test
You may have to fill out some routine paperwork before your test. The receptionist will let you know once you check-in.
Throughout the Test
The CRP test takes just a few minutes. Once you're called into the lab, you will sit in a chair. The technician will ask you which arm you want to use.
A vein, typically one near the crook of your elbow, is chosen. Then a blood draw is performed as follows:
- An elastic band is tied around your upper arm to help the vein swell.
- The skin is cleaned with an alcohol swab.
- A small needle is inserted into the vein. You may feel a slight pinch or poke. If the pain is considerable, let the technician know.
- Blood is drawn into a vacuum tube via a thin tube connected to the needle.
- After enough blood is taken, the elastic band is taken off and the needle is removed.
- Pressure is placed on the puncture site with a cotton ball, after which an adhesive bandage is applied.
7 Tips to Make Getting Blood Drawn Painless
Post-Test
Once you feel well enough to do so, you can leave. If you are feeling lightheaded or faint. let the technician or a staff member know.
After a CRP Test
When you've finished having your blood drawn, you can resume normal activities. Although there may be swelling, bruising, or pain at the injection site, the side effects tend to be mild and go away within a few days. If they don't or get worse, call your healthcare provider.
The results of a CRP or hs-CRP test are typically returned within a day or two, depending on the lab.
Follow-Up
The follow-up of a CRP test can vary based on your diagnosis. Your healthcare provider will consider your CRP results along with your symptoms and medical history, a physical exam, and other lab tests and procedures. The treatment or next steps will depend on that diagnosis.
With respect to the hs-CRP test, a repeat test may be ordered within two weeks since the results can fluctuate. If the results are borderline, the healthcare provider may take a watch-and-wait approach, re-testing after conservative measures like diet and exercise are tried.
If Your hs-CRP Is High
If your hs-CRP results are high, your healthcare may recommend drugs to help reduce your blood pressure or cholesterol, such as calcium channel blockers and statins.
American Heart Association Recommendations
The American Heart Association advises that people with CRP levels equal to or greater than 2 milligrams per liter (mg/L) may need more intense measures to prevent heart disease even if they are at borderline risk.
Based on a review of your lab tests and risk factors, other interventions may be recommended, including:
- Quitting cigarettes
- Exercising regularly, especially aerobic activities like biking or swimming
- Losing weight if overweight
- Easting a heart-healthy diet
- Managing your diabetes
- Reducing your alcohol intake
Summary
A CRP test is a type of blood test used to measure general inflammation in the body. It does so by detecting a substance called C-reactive protein, which is produced by the liver in response to inflammation.
The CRP test only requires a simple blood draw. The test cannot tell you why or where inflammation is occurring, but it can point to possible causes. There are many, including infection, pancreatitis, an autoimmune disorder, or cancer.
The high-sensitivity CRP is a variation of this test used to predict the risk of heart attack or stroke.
5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
MedlinePlus. C-reactive protein.
Muthanna FM, Ibrahim HK, Al-Awkally NA, Yousuf A, Mounich K. C-reactive protein in patients with COVID-19: a scoping review. Int J Health Sci. 2022;6:1610-20. doi:10.53730/ijhs.v6nS5.8920
Cozlea DL, Farcas DM, Nagy A, et al. The impact of C reactive protein on global cardiovascular risk on patients with coronary artery disease.Curr Health Sci J. 2013;39(4):225-231.
MedlinePlus. Erythrocyte sedimentation rate (ESR).
Arnett DK, Blumenthal RS, Albert MA, et al. 2019 ACC/AHA guideline on the primary prevention of cardiovascular disease: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Circulation.2019 Sep 10;140(11):e563-95. doi:10.1161/CIR.0000000000000677
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By Carol Eustice
Carol Eustice is a writer covering arthritis and chronic illness, who herself has been diagnosed with both rheumatoid arthritis and osteoarthritis.
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