Calprotectin is a stool (faecal) test that is used to detect inflammation in the intestines. Intestinal inflammation is associated with, for example, some bacterial infections and, in people with inflammatory bowel disease (IBD), it is associated with disease activity and severity. The calprotectin test is not diagnostic but may be used to distinguish between IBD and non-inflammatory disorders and to monitor IBD disease activity.

A doctor may order calprotectin to help investigate the cause of a person's persistent watery or bloody diarrhoea. The test may be ordered along with other stool tests, such as a stool culture to detect a bacterial infection, a stool white blood cell test, and/or a faecal occult blood test (FOBT). If a doctor suspects inflammation, then blood tests that detect inflammation in the body, such as an erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP), may also be ordered. Testing is performed both to help determine what is causing a person's symptoms and to rule out conditions with similar symptoms. This means that additional blood and stool testing may be performed depending on the suspected causes.

A calprotectin test may be ordered to help determine whether an endoscopy is indicated if IBD is suspected. A diagnosis of IBD is usually confirmed by performing an endoscopy (colonoscopy or sigmoidoscopy) to examine the intestines and by obtaining a small tissue sample (biopsy) to evaluate for inflammation and changes in tissue structures. This testing is invasive and is less likely to be necessary if inflammation is not present.

A calprotectin test may be ordered if a person with IBD has symptoms that suggest a flare-up, both to detect disease activity and to help evaluate its severity. For example, if a person has a moderately elevated calprotectin, then testing may be repeated several weeks later to see if it has stayed moderately elevated, increased, or returned to normal.

A calprotectin test may be ordered when a person has symptoms that suggest that gastrointestinal inflammation may be present and when a doctor wants to distinguish between IBD and a non-inflammatory bowel condition.

Symptoms will vary from person to person and over time. They may include one or more of the following:

• Bloody or watery diarrhoea
• Abdominal cramps or pain
• Fever
• Weight loss
• Rectal bleeding
• Weakness

Testing for calprotectin may be performed when a doctor wants to determine whether an endoscopy (colonoscopy or sigmoidoscopy) is likely or less likely to be necessary.

When a person has been diagnosed with IBD, a calprotectin test may be ordered whenever a flare-up is suspected, both to confirm disease activity and to evaluate its severity.

An elevated calprotectin indicates that inflammation is likely present in the gastrointestinal tract but does not indicate either its location or cause. In general, the degree of elevation is associated with the severity of the inflammation.

Increases in calprotectin are seen with IBD, but also with bacterial infections, some parasitic infections, and with colorectal cancer. An endoscopy (colonoscopy or sigmoidoscopy) may be indicated as a follow-up test to help determine the cause of inflammation, signs, and symptoms.

In people newly diagnosed with IBD, concentrations of calprotectin may be very high.

A low calprotectin means that signs and symptoms are likely due to a non-inflammatory bowel disorder. Examples of these include irritable bowel syndrome (IBS) and viral gastrointestinal infections. In people with low calprotectin results, an endoscopy is less likely to be indicated or useful.

A moderate calprotectin level may indicate that there is some inflammation present or that a person's condition is worsening. A repeated calprotectin test with a result that is still moderately elevated or that has increased is likely to require further investigation and may warrant an endoscopy.

Anything that causes inflammation in the intestines can cause an increase in stool calprotectin.

Calprotectin can be increased with the intestinal tissue damage and bleeding that is sometimes seen with use of non-steroidal anti-inflammatory drugs (NSAIDs).

Calprotectin is related to another stool test, lactoferrin. Both are substances that are released by white blood cells in the stool and are associated with intestinal inflammation. The clinical use of these tests is still relatively new. They are promising as non-invasive ways of evaluating intestinal inflammation and are potentially more sensitive than stool white blood cell testing, but they are not yet available in all laboratories. Of the two tests, calprotectin has been the most extensively studied and it is ordered more frequently than lactoferrin. Usually one or the other will be ordered, but not both.

In some cases, calprotectin may be low even when inflammation is present (a false negative). This is most frequently seen with children.

There is no Medicare rebate available for the faecal calprotectin test so the patient must pay the full cost of the test. This cost may vary between laboratories.

In general, no. There are blood tests used to detect inflammation (CRP, ESR), but they do not provide the same information about gastrointestinal inflammation as the stool calprotectin test.

Calprotectin is a reflection of gastrointestinal inflammation and is not affected by lifestyle changes. If it is due to an infection, then it will most likely return to normal when the infection resolves. If it is due to inflammatory bowel disease, then it will rise and fall with disease activity. In the rare case that an elevated calprotectin is caused by non-steroidal anti-inflammatory drug (NSAID) therapy, then it is likely to return to normal when the medication is discontinued.

No. This test is somewhat specialised and is not offered by all laboratories. The sample will likely be sent to a reference laboratory for testing and it may take several days before results are available.