The Vampire Study: Significant elevation of faecal calprotectin in healthy volunteers after 300？ml blood ingestion mimicking upper gastrointestinal bleeding

Faecal calprotectin correlates with histological and clinical activity in inflammatory bowel disease. Gastrointestinal bleeding might also increase faecal calprotectin levels, erroneously implying intestinal inflammation; however, this possibility has not been systematically assessed. Sixteen healthy volunteers without gastrointestinal disease and normal faecal calprotectin baseline values ingested their own blood twice, either by drinking or via nasogastric tube. Quantities of 100？ml and 300？ml blood were ingested in a randomised order, with a 28-day wash-out period. Faecal calprotectin, faecal occult blood test, and the occurrence of melaena were assessed. Faecal calprotectin？≥？50？μg/g was considered elevated. Melaena was reported by all healthy volunteers after 300？ml and by 11/15 healthy volunteers (71%) after 100？ml blood ingestion. One day after ingestion of 300？ml blood, 8/16 faecal calprotectin tests were positive compared to 1/16 at baseline (p？=？0.016). Faecal calprotectin levels above？>？200？μg/g were rarely observed. There was a trend for faecal calprotectin test positivity also after ingestion of 100？ml. Ingestion of blood resulted in an increase in faecal calprotectin-positive tests. Gastrointestinal bleeding should be considered as a potential cause of mild faecal calprotectin elevation？>？50？μg/g; however, increased faecal calprotectin above？>？250–300？μg/g, the established cut-off for relevant intestinal inflammation in patients with inflammatory bowel disease, is rare