About the Test
Purpose of the test
Doctors measure CRP because it is a marker of inflammation, which is part of the body’s fight against illness or injury. Your doctor might order a CRP test to:
- Check for infection if you have symptoms of inflammation such as fever, chills, redness or flushing, nausea, vomiting, rapid breathing, and/or rapid heart rate.
- Guide treatment of sepsis, a life-threatening complication where the body’s response to a bacterial infection triggers inflammation throughout the body.
- Monitor flare-ups of a chronic inflammatory autoimmune disease such as lupus or rheumatoid arthritis.
- Assess the treatment of a chronic inflammatory condition.
What does the test measure?
The test measures the amount of CRP in your blood. CRP levels can reflect the presence and severity of inflammation in your body.
CRP is a protein produced by the liver. When bacteria or other cellular invaders threaten the body, the liver releases CRP into the bloodstream to help organize the body’s defenses. This early response is called an acute phase response. It is also referred to as inflammation or aninflammatory response. The acute phase response also can occur in chronic conditions, including some autoimmune diseases.
As an early responder, CRP is technically known as a positive acute phase reactant. Its level, measured from a blood sample, gives your doctor information about the presence of inflammation and how serious it is. However, CRP levels do not tell the doctor where in your body the inflammation is located or what is causing it.
High-sensitivity CRP (hs-CRP) testing is a different form of testing that identifies very low concentrations of CRP. Although both tests measure CRP, hs-CRP is considered a separate test with distinct uses.
When should I get a CRP?
CRP testing, which might be casually referred to as inflammation testing, is done primarily to detect or monitor health conditions that are associated with inflammation. For example, a CRP test may be recommended if you have signs and symptoms of:
- Bacterial or viral infection
- Symptoms such as fever(s)
- Autoimmune disease, including rheumatoid arthritis and lupus
- Minor inflammation
There are no strict guidelines for when CRP testing is prescribed, so it is important to consult with your health care provider to determine if a CRP test or test for inflammation is appropriate in your situation.
Finding a CRP
How can I get a C-Reactive Protein test?
CRP testing is typically performed only after being prescribed by a doctor or other health professional.
After your doctor orders a CRP test, which is usually a blood test for inflammation, the blood sample can be drawn at a hospital (including your bedside) or clinic laboratory. In some cases, the sample might be collected at your doctor’s office. The measurement of CRP takes place in a laboratory.
Can I take the test at home?
Options are available for at-home CRP testing. For most of these at-home inflammation tests, you collect a blood sample at home and then mail it to a laboratory where it can be analyzed.
The blood sample for at-home CRP tests is taken from your fingertip using a very small needle called a lancet. You then apply a drop of blood to a special test paper that is processed by the lab. Results are usually provided through a secure website or smartphone app.
At-home CRP tests can be purchased without a prescription, but it is generally best to consult with your doctor before taking an at-home CRP test. Your doctor can discuss the appropriateness of testing and help interpret any test results.
How much does the test cost?
Many factors contribute to the cost of a CRP test, including the test materials, the fee for the phlebotomist who draws your blood, the laboratory’s fee for analyzing the sample, and your doctor’s office fee.
Your insurance coverage will determine your out-of-pocket cost. Insurance generally covers CRP testing, but depending on your policy, you might owe a deductible or a copay. If you are in doubt, check with your insurance provider.
If you are uninsured, then discuss the cost with your doctor, the hospital, or laboratory administrator. Some health care institutions have financial advocacy offices that can assist you with concerns about cost. Typically, you can use your FSA or HSA to pay for testing.
Taking a CRP
CRP is measured from a blood sample that comes from a vein. A small amount of blood will be drawn from your arm. It usually takes place in a hospital or clinic laboratory, but the blood draw can also be done in a doctor’s office or at the bedside in a hospital. The blood draw takes only a few minutes.
Before the test
Your doctor’s office may review your medications before the test. Some medications, including nonsteroidal anti-inflammatory drugs and statins, can impact CRP levels. Magnesium supplements also can affect your CRP level. For this reason, tell your doctor about any medications or supplements you take and ask whether you should adjust your medications before the test.
If you are taking an at-home CRP test, follow the directions in the test kit step-by-step to collect the sample correctly using a lancet. You do not need to fast for a CRP test.
During the test
A phlebotomist will take a blood sample from a vein in your arm. They will place a rubber tourniquet around your upper arm and ask you to pump your fist a few times so that the vein can be located. The technician will cleanse that area of your arm with an alcohol wipe and when the skin is dry, insert a needle and draw out a vial of blood.
There may be a brief pinching sensation when the needle is inserted. The phlebotomist will then remove the tourniquet, withdraw the needle, briefly apply pressure to the site, and place a bandage over it.
Taking a CRP test at home also takes just a few minutes. Test kit instructions may vary, so be sure to carefully read all the instructions on how to obtain your blood sample.
After the test
Providing a blood sample is a routine, low-risk procedure. There may be slight pain or bruising at the injection site, but these symptoms disappear quickly. You will be able to get on with your day and normal activities when you leave the laboratory.
Very rarely, there may be more serious effects such as light-headedness or infection.
These complications are very unlikely, but if you notice any ongoing effects after your test, make sure to contact your doctor.
Receiving test results
The results of your CRP test should be available within a business day or two depending on where the test is performed. You may receive the results via electronic communication or directly from your doctor’s office.
Interpreting test results
Your test result is the level of CRP in your blood. Depending on the laboratory’s standards, the result is expressed in milligrams per deciliter (mg/dL) or milligrams per liter (mg/L). The report might indicate that the level is high, low, or normal.
Although “normal” CRP levels vary from lab to lab, it is generally accepted that a value of 0.8-1.0 mg/dL (or 8-10 mg/L) or lower is normal. Most healthy adults have CRP levels lower than 0.3 mg/dL.
A minor elevation in CRP level—generally 0.3 to 1.0 mg/dL—does not necessarily mean you have an illness that requires treatment. CRP levels may be higher in females, patients on hormone replacement therapy, and those with high body mass index. Mildly elevated CRP can be associated with insomnia and depression. Your doctor will consider these factors when interpreting your CRP test result.
A CRP level higher than 1.0 mg/dL usually suggests that there is inflammation in your body, but it does not identify the cause or the location of that inflammation. Very high levels of CRP can be associated with various types of infections, autoimmune diseases, some cancers, and conditions affecting the lungs or pancreas. If your CRP level is in this range, your doctor may order additional tests before making a diagnosis.
Because of variations in laboratory methods and reference ranges, it is best to consult with your physician for clarity about your results.
Abnormal levels of CRP indicate your body is experiencing inflammation, which can be caused by so many different things from a minor infection to more serious autoimmune conditions or heart disease. Your symptoms and reason for seeking treatment, along with your doctor’s assessment of the potential root of your inflammation issues will dictate next steps.
Always speak with your doctor to help you interpret your results and discuss if follow-up testing or consultation is needed. Some questions you can ask your physician about your CRP test include:
- Were my CRP levels within the reference range? If not, how big of a concern is it?
- Is a minor increase in CRP something to worry about? What might be the cause?
- Is there anything I can do on my own to bring down my CRP level?
- Do you recommend additional testing? If so, what should I expect from that process?
- National Library of Medicine: Autoimmune Diseases
- National Center for Biotechnology Information: What Is an inflammation?
- National Institute of Arthritis and Musculoskeletal and Skin Diseases: Autoimmune Diseases
- National Institute of Environmental Health Sciences: Inflammation
- Veterans Health Administration: Eating to Reduce Inflammation
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