Introduction

Calprotectin is a heterodimer of calcium-binding proteins which belongs to the S-100 protein family. It is released from neutrophils and monocytes during cellular activation (or death) at sites of active inflammation, and accounts for upto 60% of the cytosolic protein in the granules of these cells. It is a highly stable protein, resists enzymatic degradation and can be detected in stool samples kept at room temperature for up to 7 days. It was first studied by Roseth et al1 in the early 1990s, both for the diagnosis of colorectal cancer and inflammatory bowel diseases (IBD). Tibble et al2 reported its efficacy in assessing intestinal inflammation in Crohn's disease (CD) in 2000 and discriminating from irritable bowel disease, with 100% sensitivity and 97% specificity at a cut-off value of 30 mg/L. There has been a steady increase in the use of faecal calprotectin (FC) in the UK in the last few years, and the National Institute for Health and Care Excellence (NICE) released a Diagnostic Guidance on Faecal Calprotectin in October 2013 (DG11) for its use in the evaluation of patients suspected to be suffering with IBD in adults.3 The test is now approved for use in primary care, and a number of clinical pathways have incorporated the FC test in the evaluation of patients with suspected IBD and also to aid diagnosis of irritable bowel syndrome (IBS).

It is important to recognise that FC is a neutrophil protein and therefore expected to be elevated in the stool of patients with any inflammatory bowel condition, such as acute resolving infective colitis, diverticulitis, and non-steroidal-induced colitis, and even in colonic adenomas and cancer. It is not a specific diagnostic test for IBD, and it should not be …