Medical Tests

C-Reactive Protein (CRP) Tests

What is a c-reactive protein (CRP) test? 

A c-reactive protein test measures the level of c-reactive protein (CRP) in your blood. CRP is a protein made by your liver. It’s sent into your bloodstream in response to inflammation. 

Inflammation is your body’s way of protecting your tissues if you’ve been injured or have an infection. It can cause pain, redness, and swelling in the injured or affected area. Some autoimmune disorders and chronic diseases can also cause inflammation. 

Normally, you have low levels of c-reactive protein in your blood. Elevated levels may be a sign of a serious infection or other disorder. 

This test may go by other names, such as c-reactive protein or high-sensitivity CRP (hs-CRP) 

What is it used for? 

A CRP test may be used to find or monitor conditions that cause inflammation. These include: 

  • Bacterial infections, such as sepsis, a severe and sometimes life-threatening condition 
  • A fungal infection 
  • Inflammatory bowel disease, a disorder that causes swelling and bleeding in the intestines 
  • An autoimmune disorder such as lupus or rheumatoid arthritis 
  • An infection of the bone called osteomyelitis 

Why do I need a CRP test? 

You may need this test if you have symptoms of a serious bacterial infection. Symptoms include: 

  • Fever 
  • Chills 
  • Rapid breathing 
  • Rapid heart rate 
  • Nausea and vomiting

If you’ve already been diagnosed with an infection or have a chronic disease, this test may be used to monitor your treatment. CRP levels rise and fall depending on how much inflammation you have. If your CRP levels go down, it’s a sign that your treatment for inflammation is working. 

A CRP test may also be used as part of your routine medical care, even if you have no symptoms.

What happens during a CRP test? 

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This process usually takes less than five minutes. 

Will I need to do anything to prepare for the test? 

You don’t need any special preparations for a CRP test. Fasting is not required before the blood draw. 

Note that medications, such as non-steroidal anti-inflammatory drugs (NSAIDs) and statins, as well as some supplements, like magnesium, may falsely reduce your CRP.  

If you have experienced a recent injury or illness, this can falsely elevate CRP levels. 

Let your doctor know about any supplements and medications you are taking or if you have had a recent injury or illness before taking the CRP test. Do not go off any medications without first talking to your provider.  

Are there any risks to the test? 

There is truly minor risk to having a blood test. You may have slight pain or bruise at the spot where the needle was put in, but most symptoms go away quickly. 

What do the results mean? 

If your results show an elevated level of CRP, it probably means you have some type of inflammation in your body. A CRP test doesn’t explain the cause or location of the inflammation. So, if your results are not normal, your health care provider may order more tests to figure out why you have inflammation. 

A higher-than-normal CRP level does not necessarily mean you have a medical condition needing treatment. Other factors can raise your CRP levels. These include cigarette smoking, obesity, and lack of exercise. 

Lab values vary, and there is no standard at present. However, in general, the result is reported in either mg/dL or mg/L. Hs-CRP is usually reported in mg/L. Below are some common ranges used in reporting CRP levels.  

  • Less than 0.3 mg/dL: Normal (level seen in most healthy adults). 
  • 0.3 to 1.0 mg/dL: Normal or minor elevation (can be seen in obesity, pregnancy, depression, diabetes, common cold, gingivitis, periodontitis, sedentary lifestyle, cigarette smoking, and genetic polymorphisms). 
  • 1.0 to 10.0 mg/dL: Moderate elevation (Systemic inflammation such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) or other autoimmune diseases, malignancies, myocardial infarction, pancreatitis, bronchitis). 
  • More than 10.0 mg/dL: Marked elevation (Acute bacterial infections, viral infections, systemic vasculitis, major trauma). 
  • More than 50.0 mg/dL: Severe elevation (Acute bacterial infections). 

Your specific values should be interpreted with the help of your doctor. If you have questions about your results, talk to your healthcare provider. 

Is there anything else I need to know about a CRP test?

A CRP test is sometimes confused with a high-sensitivity-(hs) CRP test. Although they both measure CRP, they are used to diagnose different conditions. A hs-CRP test measures much lower levels of CRP. It’s used to check for the risk of heart disease.

Source: MedlinePlus, National Library of Medicine and StatPearls