I. Introduction

The CRP test is used in the diagnosis and management of many medical conditions, including sepsis, inflammatory bowel disease (IBD), and autoimmune diseases, all of which are associated with increased inflammation. The World Health Organization estimates that sepsis affects more than 30 million people worldwide each year, contributing to as many as six million deaths. Approximately three million people were diagnosed with an inflammatory bowel disease — either ulcerative colitis or Crohn’s disease — in 2015. Autoimmune diseases affect approximately 24 million people in the United States.

This guide provides a detailed overview of the CRP test, along with information on the causes, symptoms, and treatment options for sepsis, IBD, and autoimmune diseases.

II. Overview of the CRP Test

Why should I get tested?

The purpose of the CRP test is to determine if an individual has a higher-than-normal amount of inflammation. Health care providers often order the CRP test when they want to know if a patient is having a flare-up of lupus, rheumatoid arthritis, or another autoimmune disease. The CRP test can be used to determine if a patient’s medication is working to reduce inflammation associated with a disease or medical condition. CRP testing is also used in the diagnosis and management of heart attacks, cancers, and infections.

When should I get tested?

People should have a CRP test when they have signs or symptoms that could indicate a high level of inflammation in the body. The CRP test is also performed at least once per year in people who have autoimmune diseases like Sjogren’s syndrome and lupus. Some medical professionals order the CRP test after prescribing medication to treat IBD or autoimmune diseases. In this case, the results of a CRP test help determine if the medication is working as intended.

What is required for the test?

CRP testing requires the patient to provide a blood sample.

What do I need to do to prepare for the test?

No special preparation is required for the CRP blood test.

III. The Basics of Sepsis, Inflammatory Bowel Disease, and Autoimmune Diseases


Sepsis is an example of what can happen when an individual has an “overwhelming immune response” to a bacterial organism. When a bacterial infection triggers this response, the immune system releases a flood of chemicals, resulting in inflammation that affects the entire body. The high level of inflammation reduces blood flow, leaving the organs without enough oxygen to function properly. In severe cases of sepsis, the organs begin shutting down due to the lack of oxygen and nutrients. Sepsis is more likely to occur in the elderly, infants, and children, as well as people whose immune systems have been weakened by illness or immunosuppressive medications, those with chronic illnesses, and individuals who have suffered traumatic injuries or severe burns.

The most common signs and symptoms of sepsis include fever, rapid heart rate, rapid breathing, chills, disorientation, and rash.

Inflammatory Bowel Disease

IBD is a term used to describe two conditions: ulcerative colitis and Crohn’s disease. Both conditions cause chronic inflammation of the GI tract, which can result in permanent damage. Ulcerative colitis only affects the large intestine and the rectum, while Crohn’s disease can affect any part of the gastrointestinal system, including the mouth, esophagus, and anus. Additionally, Crohn’s disease can affect several layers of the GI tract, but ulcerative colitis only affects a single layer of the colon’s lining.

Researchers do not know the exact cause of IBD, but they do know that it is a result of an overactive immune system. In people with IBD, the immune system mistakes the GI tract for something harmful, which triggers inflammation. Symptoms of IBD include abdominal pain, weight loss, bloody stools, rectal bleeding, fatigue, and persistent diarrhea.

Autoimmune Diseases

More than 80 autoimmune diseases have been identified in humans. Although these diseases may present differently, they all have one commonality: they are the result of an immune system that cannot tell the difference between harmful substances and healthy tissues. A healthy immune system protects the body by fighting bacteria, fungi, viruses, and toxins. In individuals with autoimmune diseases, the immune system attacks healthy tissue, causing permanent damage. Researchers do not know why some people develop autoimmune diseases, but genetics may play a role, as these diseases tend to run in families.

Fevers of unknown origin, muscle aches, and fatigue are some of the early symptoms of autoimmune diseases. Some autoimmune diseases also cause damage to specific organs and tissues. For example, lupus can damage heart valves or cause abnormal heart rhythms. In people with Sjogren’s syndrome, the immune system attacks the tear ducts and salivary glands, causing dry eyes and a dry mouth. Rheumatoid arthritis causes joint damage, resulting in joint pain, stiffness, and swelling.

IV. How a CRP Test Works

Before CRP can be measured, the patient must provide a blood sample. The sample is obtained via a procedure known as venipuncture, which involves piercing a vein with a needle. Venipuncture is typically performed in a doctor’s office, medical clinic, hospital, or other medical facility. During the procedure, a phlebotomist examines both arms to find the patient’s most prominent vein. Once the vein has been identified, the phlebotomist wipes the skin with an alcohol pad to remove bacteria and reduce the risk of infection. After piercing the vein, the phlebotomist uses a small tube to collect a blood sample that’s large enough to be analyzed.

C-reactive protein is measured with a method known as latex-enhanced nephelometry. To perform this procedure, laboratory personnel dilute the blood sample and mix it with latex particles that have been coated with anti-CRP antibodies. Any CRP in the blood sample will bind with the anti-CRP antibodies, forming an antigen-antibody complex. Laboratory personnel then use scattered light to determine how much CRP is present.

V. Treatments for Sepsis, Inflammatory Bowel Disease, and Autoimmune Diseases


When someone has sepsis, one of the most important aspects of treatment is maintaining blood flow to the kidneys, liver, and other organs. This is accomplished by providing intravenous fluids to the individual. Health care providers also treat the source of the infection by administering antibiotics. In cases of severe sepsis, the individual may need to use a breathing machine or receive hemodialysis until the treatment starts working and the body can begin delivering oxygen-rich blood to the organs again.

Inflammatory Bowel Disease

IBD has no known cure, but it can be treated with medications to reduce inflammation and ease other symptoms. Antibiotics, aminosalicylates, and biologic therapies are medications used to control inflammation. Antibiotics can reduce inflammation caused by too much bacteria in the GI system. Aminosalicylates prevent flare-ups by reducing inflammation, which prevents additional damage to the GI tract. Biologic therapies reduce inflammation by blocking substances that promote inflammation. Immunosuppressants and corticosteroids both reduce the activity of the immune system. Corticosteroids are usually taken during a flare-up, while immunosuppressants are used long-term. Some lifestyle changes can also relieve IBD symptoms and prevent flare-ups. For example, avoiding alcohol and highly processed foods helps some people manage their symptoms.

In severe cases of IBD, surgery may be necessary. Bowel resection, which is used to treat Crohn’s disease, involves the removal of the damaged portion of the intestine. Surgical removal of the colon can relieve the symptoms of Crohn’s disease, and it may even cure ulcerative colitis. When the colon is removed, it can no longer store and transport fecal matter. Therefore, after the surgery, the individual must use a pouch to collect waste.

Autoimmune Diseases

A variety of medications are used to treat autoimmune diseases. Nonsteroidal anti-inflammatory drugs, commonly known as NSAIDs, reduce inflammation and relieve pain. NSAIDs are among the first medications used to treat the symptoms of autoimmune disease. These drugs work by blocking enzymes that play a role in the development of inflammation. Glucocorticoids are used to inhibit the activity of cytokines, which are proteins involved in the communication between cells. Some cytokines are pro-inflammatory, which means they promote inflammation. Inhibiting the effects of these cytokines can relieve inflammation, pain, and other symptoms of autoimmune diseases. Although glucocorticoids are highly effective, they can cause undesirable side effects. As a result, they are often taken in small doses.

Conventional disease-modifying antirheumatic drugs also reduce inflammation, but the side effects are more tolerable than the ones produced by glucocorticoids. cDMARDs are typically used to treat rheumatoid arthritis and other autoimmune disorders known for damaging the joints. Not only do cDMARDS relieve inflammation, but they can also prevent an autoimmune disease from becoming worse. Like glucocorticoids, anti-TNF biologics inhibit the expression of cytokines that promote inflammation. These drugs are often used to treat rheumatoid arthritis, Crohn’s disease, and ankylosing spondylitis.


What is a normal CRP level?

Laboratories use different reference ranges for the CRP test, so what is normal according to one laboratory may not be normal according to another laboratory; however, healthy individuals normally have low levels of CRP in their blood.

If my CRP is high, does that mean I have some kind of disease or disorder?

Not necessarily. A high CRP level can be caused by many conditions and situations, including connective tissue disease, cancer, rheumatoid arthritis, heart attack, infection, lupus, and other diseases. Elevated CRP levels can also be caused by tobacco use, lack of physical activity, and obesity, so just because an individual has a high CRP does not mean there is an underlying disease or disorder.

My doctor wants me to have the hs-CRP test. Is this the same as the CRP test?

The CRP test and the hs-CRP test are similar, but they are not exactly the same. While the CRP test is used in the diagnosis and management of inflammatory conditions, the hs-CRP test detects much smaller quantities of CRP in the blood, making it useful for determining whether an individual has an increased risk of heart disease. Another difference between the two tests is that it costs less to perform the standard CRP test than it does to perform the hs-CRP test.

Can any of my medications affect my CRP level?

Yes. Some medications are known to reduce CRP levels, which can have an effect on the results of the CRP test. These medications include aspirin, antioxidants, ACE inhibitors used to control high blood pressure, and drugs used to reduce cholesterol levels. Individuals taking any of these medications should inform their doctor before having the CRP test.

If my CRP level is elevated, will I need more tests?

Probably. Although the CRP test is useful for determining if an individual has a high level of inflammation, it does not identify the exact cause of the inflammation. Therefore, more tests may be needed to determine the cause of an individual’s symptoms. If a health care provider suspects that an individual has an autoimmune disease, the ANA test can help determine if the individual has antinuclear antibodies in their blood. Antinuclear antibodies attack healthy cells, damaging the tissues and causing the symptoms of autoimmune disorders like lupus, rheumatoid arthritis, scleroderma, and Sjogren’s syndrome.

The anti-dsDNA test is also used in the diagnosis of autoimmune disorders. This test determines if an individual has antibodies to double-stranded DNA in their blood. These antibodies damage a person’s DNA, causing symptoms such as fatigue, joint pain, muscle aches, and fevers of unknown origin. If a medical professional suspects that cancer is the cause of an individual’s symptoms, the complete blood count can be used to determine if the person has a normal number of white blood cells, red blood cells, hemoglobin, and platelets.

Do some people have higher levels of CRP than others?

Yes. CRP levels tend to be higher in older people, African Americans, and women.

Are there any risks to having the CRP test?

Because the CRP test involves providing a blood sample, there is a slight risk of having a bacterial infection develop after the blood draw. In some individuals, soreness and bruising occur at the venipuncture site.

VII. Additional Resources

For more information on sepsis, inflammatory bowel disease, and autoimmune diseases, along with testing for these conditions, visit the following resources.

Centers for Disease Control and Preventionwww.cdc.gov/sepsisThe CDC offers printable fact sheets with more information about sepsis.
Crohn’s & Colitis Foundationwww.crohnscolitisfoundation.orgAccess resources provided by the Crohn’s & Colitis Foundation.
American Autoimmune Related Diseases Associationwww.aarda.org/diseaselistAARDA provides information on more than 100 autoimmune diseases and autoimmune-related diseases.
University of Michiganwww.uofmhealth.orgLearn more about the tests used to diagnose autoimmune diseases.
The Cleveland Clinicwww.my.clevelandclinic.orgExperts from the Cleveland Clinic offer a detailed overview of IBD, including the tests used to diagnose it.

VIII. Sources Used in This Article