Background: Fecal calprotectin (fC), a calcium binding protein abundant in neutrophiles, is increasingly gaining importance as a noninvasive biomarker for intestinal inflammation. It correlates with histological and clinical activity in inflammatory bowel disorders (IBD) and predicts IBD relapse. However, gastrointestinal (GI) bleeding might induce elevated fC levels, erroneously suggesting intestinal inflammation. To the best of our knowledge, the interference of intraluminal blood in the GI tract on fC values has not yet been systematically assessed.
Methods: 15 healthy volunteers (HV) (mean age 25 years, range 23–33 years) without GI symptoms or known GI disease and normal fC baseline values ingested 100 and 300ml of their own blood in a randomized order by drinking or via nasogastric tube, with a 28 day wash out period. fC and fecal occult blood test (FOBT) as well as the occurrence of visible melena were assessed at baseline, on day 0–7 and 14. fC was measured by a commercially available particle-enhanced turbidimetric immunoassay (Buehlmann Laboratories Ltd, Switzerland). fC >50 ug/g was defined elevated.
Results: Ingestion of blood was tolerated well by all HV with only slight symptoms such as nausea in 7/15 HV (46%), lasting <24 hours. Melena was reported by all 15 HV after 300ml and by 10 out of 14 HV after 100ml blood ingestion (71%). Upon ingestion of 300ml blood mean fC levels rose significantly within 5 days compared to baseline (p=0.0025) and at least one fC value above 50ug/g was observed in 9/15 (60%) of HV.
Increase in fC levels after ingestion of 100ml was also significant over baseline (p=0.028); calprotectin levels above 50ug/g were observed in 7/15 (46%) of HV. Pronounced increases in fC levels above 200ug/g were rarely observed (1 individual (6%) after 100ml, none after 300ml ingestion).
FOBT testing became positive in 14/15 (93%) after 300ml and 6/14 (40%) after 100ml blood, respectively. FOBT and fC levels showed a positive correlation, fC levels being significantly higher in FOBT-positive samples than FOBT-negative (p<0.0001).
Conclusions: Ingestion of 100ml and 300ml blood led to significant fC rise in the majority of participants. Very high fC levels (>200ug/g) were rarely observed (6% of participants). We conclude that upper GI-Bleeding should be considered as a potential reason for otherwise unexplained mild fC elevation.