Calprotectin is a stool test that measures intestinal inflammation. Specifically, it detects a protein released by white blood cells called neutrophils when they rush to an inflamed area in your gut. A level below 50 micrograms per gram (µg/g) is generally considered normal in adults and children over age 4, while higher levels signal that something is actively irritating or inflaming your intestinal lining.
The test is most commonly used to distinguish between inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), two conditions that can cause similar symptoms but require very different treatment. It’s also used to track how well IBD treatment is working over time.
What Calprotectin Actually Detects
Calprotectin is a protein that makes up about 60% of the soluble protein content inside neutrophils, a type of white blood cell that acts as your immune system’s first responder. When your intestinal lining is inflamed, neutrophils swarm to the area. As they fight, get damaged, or die, they release calprotectin into the surrounding tissue, and it ends up in your stool.
The protein itself has antimicrobial properties, meaning it helps your body fight off invaders by binding calcium and starving bacteria of essential metals. But from a diagnostic perspective, what matters is the sheer quantity: the more neutrophils that have gathered and broken down in your gut, the more calprotectin shows up in your stool. That makes it a remarkably direct measure of intestinal inflammation, more so than blood tests, which reflect inflammation happening anywhere in the body.
Why It’s Better Than a Blood Test
Blood markers like C-reactive protein (CRP) are commonly used to check for inflammation, but they aren’t gut-specific. CRP rises with a sore throat, a joint flare, or a skin infection. Calprotectin, because it’s measured in stool, reflects what’s happening specifically in your intestines.
In a study of 335 people comparing the two tests, calprotectin distinguished IBD from IBS with 93% sensitivity and 91% specificity, while CRP managed only 83% sensitivity and 86% specificity. The difference is even more striking when you look at the raw numbers: people with ulcerative colitis had median calprotectin levels of 1,710 µg/g, those with Crohn’s disease had levels around 560 µg/g, and people with IBS had levels of just 18 µg/g. That kind of gap makes calprotectin far more useful for sorting out what’s causing chronic diarrhea or abdominal pain.
How to Read Your Results
Most labs use 50 µg/g as the standard cutoff between normal and elevated. At that threshold, the test catches essentially 100% of IBD cases, though specificity is lower at around 60%, meaning some people without IBD will still have mildly elevated results. A large analysis pooling data from nearly 6,000 patients found overall sensitivity of 95% and specificity of 91% for detecting IBD.
In practice, results tend to fall into three zones:
- Below 50 µg/g: Normal. Intestinal inflammation is unlikely, and IBD is very improbable. One study found that values below 8 µg/g predicted completely normal colonoscopy and biopsy results in 42% of patients referred for chronic diarrhea.
- 50 to 250 µg/g: Borderline to moderately elevated. Could reflect mild inflammation, an infection, medication effects, or early IBD. Your doctor will likely repeat the test or recommend further investigation.
- Above 250 µg/g: Significantly elevated. Strongly suggests active intestinal inflammation and typically leads to colonoscopy for a definitive diagnosis.
For people already diagnosed with ulcerative colitis, more specific cutoffs help gauge disease severity. Levels below 60 µg/g suggest full remission, levels above 110 µg/g indicate at least moderate disease activity, and levels above 310 µg/g point to severe inflammation.
Tracking Treatment Over Time
One of calprotectin’s most valuable uses is monitoring whether IBD treatment is actually healing the gut lining, not just reducing symptoms. You can feel better while still having inflammation that slowly damages your intestines. Calprotectin correlates well with what doctors see during colonoscopy, often better than symptoms, blood tests, or how you feel day to day.
In a study of ulcerative colitis patients, those who achieved two consecutive calprotectin readings below 250 µg/g after starting treatment all showed mucosal healing on follow-up colonoscopy. It took a median of four months to reach that target, with a range of two to ten months. Levels below 50 µg/g correlated with complete endoscopic remission. This means calprotectin can sometimes replace repeat colonoscopies, sparing you the prep and procedure while still confirming your gut is healing.
Rising calprotectin levels in someone whose IBD had been quiet can also signal a relapse before symptoms return, giving doctors a window to adjust treatment early.
What Else Can Raise Your Levels
IBD isn’t the only thing that elevates calprotectin. Levels rise with gastrointestinal infections, colorectal cancer, polyps, celiac disease, peptic ulcers, and acute appendicitis. A meta-analysis found calprotectin detected colorectal cancer with 87% sensitivity and 76% specificity, though it’s not used as a primary cancer screening tool.
Medications are a common and often overlooked cause of falsely elevated results. NSAIDs (like ibuprofen and naproxen) and proton pump inhibitors (PPIs, used for acid reflux) both raise calprotectin levels significantly. In patients with functional bowel disorders, those taking PPIs had median calprotectin levels of 66 µg/g compared to 23 µg/g in those not taking them. NSAID users showed 57 µg/g versus 25 µg/g. The effect of PPIs faded with time, so the closer your prescription is to the test date, the more it may skew results. If you’re taking either medication, mention it to your doctor before interpreting a borderline result.
Children Have Naturally Higher Levels
Calprotectin levels in young children are much higher than in adults, and this is completely normal. Newborns under one month old average around 258 µg/g, a level that would be alarming in an adult. Babies between one and six months average about 239 µg/g, with a transient spike around six to twelve months that can reach 250 µg/g. Levels then gradually decline: toddlers aged two to three average 75 µg/g, and by age three to four, levels drop to about 34 µg/g, approaching the adult range.
The standard 50 µg/g cutoff only applies reliably to children over age four. For younger children, elevated results need to be interpreted against age-appropriate reference ranges, or they’ll trigger unnecessary concern.
How the Test Works for You
The test itself is simple. You collect a small stool sample at home, typically using a container your doctor’s office or lab provides. No special preparation, fasting, or dietary changes are required. The sample stays stable for up to seven days at room temperature or eleven days refrigerated, so you don’t need to rush it to the lab the same day. If there’s a longer delay, freezing the sample preserves it.
Results usually come back within a few days. Because calprotectin levels can fluctuate, a single borderline result doesn’t necessarily mean something is wrong. Doctors often repeat the test or pair it with other information before making decisions. For ongoing IBD monitoring, serial measurements over weeks or months give a much clearer picture than any single number.