Other studies, such as C-reactive protein (CRP) and HLA B27 are poorly sensitive or specific.45–48 Faecal or serum calprotectin has also been associated with subclinical gut inflammation in SpA patients,49–52 although faecal calprotectin levels may be influenced by non-steroidal anti-inflammatory drug use, which is common in SpA patients.50 However, in most cases the confirmation of IBD or SpA requires advanced or interventional procedures, such as musculoskeletal MRI, arthrocentesis and synovial fluid examination, gastrointestinal imaging, endoscopy or biopsy. Here, CRP is linked to inflammatory bowel disease.