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If you have an increase in your Crohn's or colitis symptoms, your doctor may recommend certain blood and stool tests to assess for inflammation. While these tests can’t tell you if you have IBD, they can help your doctor determine if you’re responding to your medication or if you need additional tests or procedures (such as checking your medication levels, testing for fecal infections, or performing a colonoscopy or endoscopy).
It’s important to know what these lab tests are and how often you should be getting them so you can stay on top of your care and ensure you’re getting the best care possible from your care team.
The 3 most common inflammatory lab tests your doctor might order are fecal calprotectin, C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR).
Fecal calprotectin test
The fecal calprotectin test is a stool (poop) test that checks for a protein called calprotectin which is released by your white blood cells when you have inflammation. High levels of calprotectin in your stool could mean you have inflammation in your intestines.
Your doctor may use this test to monitor the activity of your IBD and assess whether you’re responding to your medication. The fecal calprotectin test can also be helpful in distinguishing between IBD and irritable bowel syndrome (IBS), a condition that can have similar symptoms to IBD but doesn’t involve intestinal inflammation.
A key limitation of the fecal calprotectin test is that calprotectin levels can also be elevated due to other conditions like fecal infections, so it can’t be used to determine if you actually have IBD. This test may also be less accurate if you have proctitis compared to left-sided colitis or pancolitis.
A test result below 50 μg/g is generally considered by many test kit manufacturers to be in the normal range for the healthy population. An elevated test result might indicate that you have inflammation in your intestines but it doesn’t tell you where the inflammation is located, the degree to which the bowel is inflamed, or what’s causing it.
Generally, higher fecal calprotectin test results are indicative of more severe inflammation while lower test results are indicative of less severe inflammation.
C-reactive protein (CRP) test
The C-reactive protein test is a blood test that checks whether you may have inflammation somewhere in your body. The test measures a protein that is made by your liver that becomes elevated quickly when your body is experiencing inflammation. While CRP cannot be used to determine if you have IBD, your doctor may use it to monitor your disease activity or determine if you’re responding to certain treatments.
It’s important to note that not everyone with IBD-related inflammation will have an elevated CRP level. In fact, some studies suggest that up to 40% of people with IBD with mild inflammation may have normal CRP levels. As a result, your doctor may use this test alongside other tests and procedures to assess your inflammation.
A test result below 5 mg/dL is considered normal according to the 2023 American College of Gastroenterology guidelines for ulcerative colitis. Higher levels of CRP are generally associated with more severe disease activity while lower levels are associated with lower disease activity.
Erythrocyte sedimentation rate (ESR) test
Like CRP, erythrocyte sedimentation rate is a blood test that measures inflammation anywhere in your body. This test measures how quickly your red blood cells fall to the bottom of a tube in a lab - the faster they fall, the more likely you are to have inflammation.
While ESR cannot be used to determine if you have IBD, your doctor may use it to monitor your disease activity over time. Like CRP, ESR may not be elevated in everyone with IBD who experiences active disease, so your doctor may use this test alongside other tests and procedures to assess your inflammation.
ESR results can be influenced by a number of factors including your age and gender. Generally, test results less than 15-30 mm/hr are considered normal for adults.
When and how to reach out to your doctor
If you start to experience new or worsening symptoms, we recommend talking to your doctor to determine if you have new or worsening inflammation.
Because symptoms are poorly correlated with inflammation, certain tests like fecal calprotectin, C-reactive protein, and erythrocyte sedimentation rate may be used to give you and your doctor an idea of whether your symptoms could be related to inflammation or something else.
If you notice your symptoms are getting worse, here’s a sample script you can use to message your doctor to let them know. Remember, you’re not being a burden to your doctor by letting them know about your symptoms. They can only help you if they know what you’re going through, so don’t hesitate to message them as soon as something comes up.
“Hi Dr. [name of your doctor],
I’ve recently noticed an increase in symptoms including [increased bowel movement trips, blood in stool, nausea, etc]. Can you please put in an order to check my CRP, ESR, fecal calprotectin, and stool PCR to rule out active inflammation and fecal infections?
Let me know if there’s anything else you want me to do.
[your name here]”
Get professional support
If you're experiencing symptoms when you consume certain foods or are dealing with chronic fatigue, your diet could be playing a role.
Our IBD-specialized registered dietitians can help you sustainably reduce your symptoms and boost your energy so that you can feel like yourself again. Request a consultation to learn if our nutrition counseling program is right for you.
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