Calprotectin

Calprotectin is an inflammation marker from neutrophil granulocytes, measured in stool, showing how many of these immune cells are active in the intestinal wall. It is looked at when assessing inflammatory bowel conditions.

What calprotectin does in the body

Calprotectin is a protein complex made of the building blocks S100A8 and S100A9 that is found in large amounts inside neutrophil granulocytes – the immune cells that are the first to migrate into tissue during inflammation. Calprotectin binds zinc and manganese very tightly and thereby withholds these trace elements from bacteria and fungi, which need them to grow. When granulocytes migrate into the gut lining, calprotectin passes with them and from disintegrating cells into the gut contents. There it is hardly broken down and remains stable in stool for several days – which is why the amount in stool reflects how many granulocytes are active in the gut wall.

Low calprotectin – what does it mean?

A low value is the normal case: only a few granulocytes are present in the gut lining, so active inflammation in which immune cells migrate into the gut wall in larger numbers is unlikely. Complaints such as bloating or altered bowel habits can still be present – they then usually have causes that do not involve granulocyte migration, for example in digestion or gut movement.

Raised calprotectin – what happens in the body?

A raised value shows that granulocytes are migrating into the gut lining in greater numbers. They are attracted by messengers that the lining releases when it is irritated by pathogens, harmful substances or an immune reaction. There the granulocytes release enzymes and reactive oxygen compounds to kill pathogens; in the process the lining itself is also attacked, the barrier becomes more permeable, and fluid and sometimes blood pass into the gut – with diarrhoea, abdominal pain and mucus in the stool. Raised values occur with bacterial gut infections, with chronic inflammatory bowel diseases such as Crohn's disease and ulcerative colitis, with diverticulitis and with painkillers from the NSAID group and acid blockers. How far the value rises depends mainly on how extensive the inflammation is.

The interpretation is given in your report.